View AD7328BRUZ_494327.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

8-Channel, Software-Selectable True Bipolar Input, 12-Bit Plus Sign ADC AD7328
FEATURES
12-bit plus sign SAR ADC True bipolar input ranges Software-selectable input ranges 10 V, 5 V, 2.5 V, 0 V to +10 V 1 MSPS throughput rate Eight analog input channels with channel sequencer Single-ended, true differential, and pseudo differential analog input capability High analog input impedance Low power: 21 mW Temperature indicator Full power signal bandwidth: 22 MHz Internal 2.5 V reference High speed serial interface Power-down modes 20-lead TSSOP package iCMOSTM process technology
FUNCTIONAL BLOCK DIAGRAM
VDD REFIN/OUT VCC
AD7328
VIN0 VIN1 VIN2 VIN3 VIN4 VIN5 VIN6 VIN7 I/P MUX T/H 2.5V VREF
13-BIT SUCCESSIVE APPROXIMATION ADC
TEMPERATURE INDICATOR DOUT CONTROL LOGIC AND REGISTERS SCLK CS DIN VDRIVE AGND VSS DGND
CHANNEL SEQUENCER
Figure 1.
GENERAL DESCRIPTION
The AD7328 1 is an 8-channel, 12-bit plus sign, successive approximation ADC designed on the iCMOS (industrial CMOS) process. iCMOS is a process combining high voltage silicon with submicron CMOS and complementary bipolar technologies. It enables the development of a wide range of high performance analog ICs capable of 33 V operation in a footprint that no previous generation of high voltage parts could achieve. Unlike analog ICs using conventional CMOS processes, iCMOS components can accept bipolar input signals while providing increased performance, dramatically reduced power consumption, and reduced package size. The AD7328 can accept true bipolar analog input signals. The AD7328 has four software-selectable input ranges, 10 V, 5 V, 2.5 V, and 0 V to +10 V. Each analog input channel can be independently programmed to one of the four input ranges. The analog input channels on the AD7328 can be programmed to be single-ended, true differential, or pseudo differential. The ADC contains a 2.5 V internal reference. The AD7328 also allows for external reference operation. If a 3 V reference is applied to the REFIN/OUT pin, the AD7328 can accept a true bipolar 12 V analog input. Minimum 12 V VDD and VSS supplies are required for the 12 V input range. The ADC has a high speed serial interface that can operate at throughput rates up to 1 MSPS.
PRODUCT HIGHLIGHTS
1. 2. The AD7328 can accept true bipolar analog input signals, 10 V, 5 V, 2.5 V, and 0 V to +10 V unipolar signals. The eight analog inputs can be configured as eight singleended inputs, four true differential input pairs, four pseudo differential inputs, or seven pseudo differential inputs. 1 MSPS serial interface. SPI(R)-/QSPITM-/DSP-/MICROWIRETMcompatible interface. Low power, 30 mW, at a maximum throughput rate of 1 MSPS. Channel sequencer.
Throughput Rate 1000 kSPS 500 kSPS 1000 kSPS 500 kSPS 1000 kSPS 500 kSPS Number of Channels 8 8 4 4 2 2
3. 4. 5.
Table 1. Similar Product Selection
Device Number AD7329 AD7327 AD7324 AD7323 AD7322 AD7321 Number of Bits 12-bit plus sign 12-bit plus sign 12-bit plus sign 12-bit plus sign 12-bit plus sign 12-bit plus sign
1
Protected by U.S. Patent No. 6,731,232.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2006 Analog Devices, Inc. All rights reserved.
04852-001
AD7328 TABLE OF CONTENTS
Features .............................................................................................. 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Product Highlights ........................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Timing Specifications .................................................................. 6 Absolute Maximum Ratings............................................................ 7 ESD Caution.................................................................................. 7 Pin Configuration and Function Descriptions............................. 8 Typical Performance Characteristics ............................................. 9 Terminology .................................................................................... 13 Theory of Operation ...................................................................... 15 Circuit Information.................................................................... 15 Converter Operation.................................................................. 15 Analog Input Structure.............................................................. 16 Typical Connection Diagram ................................................... 18 Analog Input ............................................................................... 18 Driver Amplifier Choice............................................................ 20 Registers ........................................................................................... 21 Addressing Registers .................................................................. 21 Control Register ......................................................................... 22 Sequence Register....................................................................... 24 Range Registers........................................................................... 24 Sequencer Operation ..................................................................... 25 Reference ..................................................................................... 27 VDRIVE............................................................................................ 27 Temperature Indicator............................................................... 27 Modes of Operation ....................................................................... 28 Normal Mode.............................................................................. 28 Full Shutdown Mode.................................................................. 28 Autoshutdown Mode ................................................................. 29 Autostandby Mode..................................................................... 29 Power vs. Throughput Rate....................................................... 30 Serial Interface ................................................................................ 31 Microprocessor Interfacing........................................................... 32 AD7328 to ADSP-21xx.............................................................. 32 AD7328 to ADSP-BF53x ........................................................... 32 Application Hints ........................................................................... 33 Layout and Grounding .............................................................. 33 Outline Dimensions ....................................................................... 34 Ordering Guide .......................................................................... 34
REVISION HISTORY
6/06--Rev. 0 to Rev. A Changes to Table 1............................................................................ 1 Changes to Specifications ................................................................ 3 Added Thermal Hysteresis to Terminology Section.................. 14 Change to Figure 42 ....................................................................... 20 Change to Control Register Section............................................. 23 10/05--Revision 0: Initial Version
Rev. A | Page 2 of 36
AD7328 SPECIFICATIONS
Unless otherwise noted, VDD = 12 V to 16.5 V, VSS = -12 V to -16.5 V, VCC = 4.75 V to 5.25 V, VDRIVE = 2.7 V to 5.25 V, VREF = 2.5 V to 3.0 V internal/external, fSCLK = 20 MHz, fS = 1 MSPS, TA = TMAX to TMIN. With VCC < 4.75 V, all specifications are typical. Table 2.
Parameter 1 DYNAMIC PERFORMANCE Signal-to-Noise Ratio (SNR) 2 Signal-to-Noise + Distortion (SINAD)2 Min 76 72.5 75 76 72 72.5 Total Harmonic Distortion (THD)2 -82 -77 -80 Peak Harmonic or Spurious Noise (SFDR)2 -82 -78 -79 Intermodulation Distortion (IMD)2 Second-Order Terms Third-Order Terms Aperture Delay 3 Aperture Jitter3 Common-Mode Rejection Ratio (CMRR)2 Channel-to-Channel Isolation2 Full Power Bandwidth DC ACCURACY 4 Resolution No Missing Codes -80 -80 B Version Typ Max Unit dB dB dB dB dB dB dB dB dB dB dB dB dB dB Test Conditions/Comments fIN = 50 kHz sine wave Differential mode Single-ended/pseudo differential mode Differential mode; 2.5 V and 5 V ranges Differential mode; 0 V to +10 V and 10 V ranges Single-ended/pseudo differential mode; 2.5 V and 5 V ranges Single-ended/pseudo differential mode; 0 V to +10 V and 10 V ranges Differential mode; 2.5 V and 5 V ranges Differential mode; 0 V to +10 V and 10 V ranges Single-ended/pseudo differential mode; 2.5 V and 5 V ranges Single-ended/pseudo differential mode; 0 V to +10 V and 10 V ranges Differential mode; 2.5 V and 5 V ranges Differential mode; 0 V to +10 V and 10 V ranges Single-ended/pseudo differential mode; 2.5 V and 5 V ranges Single-ended/pseudo differential mode; 0 V to +10 V and 10 V ranges fa = 50 kHz, fb = 30 kHz
-88 -90 7 50 -79 -72 22 5 13 12-bit plus sign 11-bit plus sign 1.1 1 -0.7/+1.2
dB dB ns ps dB dB MHz MHz Bits Bits Bits LSB LSB LSB LSB LSB LSB
Up to 100 kHz ripple frequency; see Figure 17 fIN on unselected channels up to 100 kHz; see Figure 14 At 3 dB At 0.1 dB All specifications are typical for 0 V to 10 V mode. Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Single-ended/pseudo differential mode (LSB = FSR/8192) Differential mode; guaranteed no missing codes to 13 bits Single-ended mode; guaranteed no missing codes to 12 bits Single-ended/psuedo differential mode (LSB = FSR/8192)
Integral Nonlinearity2
Differential Nonlinearity2
-0.9/+1.5 0.9 -0.7/+1
Rev. A | Page 3 of 36
AD7328
Parameter 1 Offset Error2, 5 Offset Error Match2, 5 Gain Error2, 5 Gain Error Match2, 5 Positive Full-Scale Error2, 6 Positive Full-Scale Error Match2, 6 Bipolar Zero Error2, 6 Bipolar Zero Error Match2, 6 Negative Full-Scale Error2, 6 Negative Full-Scale Error Match2, 6 ANALOG INPUT Input Voltage Ranges (Programmed via Range Register) Min B Version Typ Max -4/+9 -7/+10 0.6 0.5 8 14 0.5 0.5 4 7 0.5 0.5 8.5 7.5 0.5 0.5 4 6 0.5 0.5 Unit LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB Test Conditions/Comments Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Single-ended/pseudo differential mode Differential mode Reference = 2.5 V; see Table 6 VDD = 10 V min, VSS = -10 V min, VCC = 2.7 V to 5.25 V VDD = 5 V min, VSS = -5 V min, VCC = 2.7 V to 5.25 V VDD = 5 V min, VSS = - 5 V min, VCC = 2.7 V to 5.25 V VDD = 10 V min, VSS = AGND min, VCC = 2.7 V to 5.25 V VDD = 16.5 V, VSS = -16.5 V, VCC = 5 V; see Figure 40 and Figure 41 Reference = 2.5 V; range = 10 V Reference = 2.5 V; range = 5 V Reference = 2.5 V; range = 2.5 V Reference = 2.5 V; range = 0 V to +10 V VIN = VDD or VSS When in track, 10 V range When in track, 5 V and 0 V to +10 V ranges When in track, 2.5 V range When in hold, all ranges
10 5 2.5 0 to 10
V V V V
Pseudo Differential VIN(-) Input Range 3.5 6 5 +3/-5 DC Leakage Current Input Capacitance3 200 13.5 16.5 21.5 3 2.5 10 2.5 150 50 5 10 25 6 7 3 1 V V V V nA pF pF pF pF V A pF V ppm ppm mV mV ppm/C ppm/C
Rev. A | Page 4 of 36
REFERENCE INPUT/OUTPUT Input Voltage Range Input DC Leakage Current Input Capacitance Reference Output Voltage Long Term Stability Output Voltage Hysteresis2 Reference Output Voltage Error @ 25C Reference Output Voltage TMIN to TMAX Reference Temperature Coefficient Reference Output Impedance
For 1000 hours
AD7328
Parameter 1 LOGIC INPUTS Input High Voltage, VINH Input Low Voltage, VINL Input Current, IIN Input Capacitance, CIN3 LOGIC OUTPUTS Output High Voltage, VOH Output Low Voltage, VOL Floating-State Leakage Current Floating-State Output Capacitance3 Output Coding CONVERSION RATE Conversion Time Track-and-Hold Acquisition Time2, 3 Throughput Rate POWER REQUIREMENTS VDD VSS VCC VDRIVE Normal Mode (Static) Normal Mode (Operational) IDD ISS ICC and IDRIVE Autostandby Mode (Dynamic) IDD ISS ICC and IDRIVE Autoshutdown Mode (Static) IDD ISS ICC and IDRIVE Full Shutdown Mode IDD ISS ICC and IDRIVE POWER DISSIPATION Normal Mode Full Shutdown Mode
1 2 3
Min 2.4
B Version Typ
Max
Unit V V V A pF V
Test Conditions/Comments
0.8 0.4 1 10 VDRIVE - 0.2 0.4 1 5 Straight natural binary Twos complement 800 305 1 770 12 -12 2.7 2.7 0.9 360 410 3.2 200 210 1.3 1 1 1 1 1 1 30 21 38.25 16.5 -16.5 5.25 5.25
VCC = 4.75 V to 5.25 V VCC = 2.7 to 3.6 V VIN = 0 V or VDRIVE
ISOURCE = 200 A ISINK = 200 A
V A pF
Coding bit set to 1 in control register Coding bit set to 0 in control register ns ns MSPS kSPS V V V V mA A A mA A A mA A A A A A A mW mW W 16 SCLK cycles with SCLK = 20 MHz Full-scale step input; see the Terminology section See the Serial Interface section; VCC = 4.75 V to 5.25 V VCC < 4.75 V Digital inputs = 0 V or VDRIVE See Table 6 See Table 6 See Table 6; typical specifications for VCC < 4.75 V VDD/VSS = 16.5 V, VCC/VDRIVE = 5.25 V fSAMPLE = 1 MSPS VDD = 16.5 V VSS = -16.5 V VCC/VDRIVE = 5.25 V fSAMPLE = 250 kSPS VDD = 16.5 V VSS = -16.5 V VCC/VDRIVE = 5.25 V SCLK on or off VDD = 16.5 V VSS = -16.5 V VCC/VDRIVE = 5.25 V SCLK on or off VDD = 16.5 V VSS = -16.5 V VCC/VDRIVE = 5.25 V VDD = 16.5 V, VSS = -16.5 V, VCC = 5.25 V VDD = 12 V, VSS = -12 V, VCC = 5 V VDD = 16.5 V, VSS = -16.5 V, VCC = 5.25 V
Temperature range is -40C to +85C. See the Terminology section. Sample tested during initial release to ensure compliance. 4 For dc accuracy specifications, the LSB size for differential mode is FSR/8192. For single-ended mode/pseudo differential mode, the LSB size is FSR/4096, unless otherwise noted. 5 Unipolar 0 V to 10 V range with straight binary output coding. 6 Bipolar range with twos complement output coding. Rev. A | Page 5 of 36
AD7328
TIMING SPECIFICATIONS
VDD = 12 V to 16.5 V, VSS = -12 V to -16.5 V, VCC = 2.7 V to 5.25 V, VDRIVE = 2.7 V to 5.25 V, VREF = 2.5 V to 3.0 V internal/external, TA = TMAX to TMIN. Timing specifications apply with a 32 pF load, unless otherwise noted. 1 Table 3.
Parameter fSCLK tCONVERT tQUIET t1 t2 2 t3 t4 t5 t6 t7 t8 t9 t10 tPOWER-UP Limit at TMIN, TMAX VCC < 4.75 V VCC = 4.75 V to 5.25 V 50 50 14 20 16 x tSCLK 16 x tSCLK 75 60 12 5 25 20 45 35 26 14 57 43 0.4 x tSCLK 0.4 x tSCLK 0.4 x tSCLK 0.4 x tSCLK 13 8 40 22 10 9 4 4 2 2 750 750 500 500 25 25 Unit kHz min MHz max ns max ns min ns min ns min ns min ns max ns max ns min ns min ns min ns max ns min ns min ns min ns max s max s typ Description VDRIVE VCC
tSCLK = 1/fSCLK Minimum time between end of serial read and next falling edge of CS Minimum CS pulse width CS to SCLK set-up time; bipolar input ranges (10 V, 5 V, 2.5 V) Unipolar input range (0 V to 10 V) Delay from CS until DOUT three-state disabled Data access time after SCLK falling edge SCLK low pulse width SCLK high pulse width SCLK to data valid hold time SCLK falling edge to DOUT high impedance SCLK falling edge to DOUT high impedance DIN set-up time prior to SCLK falling edge DIN hold time after SCLK falling edge Power up from autostandby Power up from full shutdown/autoshutdown mode, internal reference Power up from full shutdown/autoshutdown mode, external reference
1 2
Sample tested during initial release to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of VDRIVE) and timed from a voltage level of 1.6 V. When using the 0 V to 10 V unipolar range, running at 1 MSPS throughput rate with t2 at 20 ns, the mark space ratio needs to be limited to 50:50.
t1
CS
t2
SCLK 1 2 3 4 3 IDENTIFICATION BITS
tCONVERT t6
5 13 14 15 16
t3
t4
DB11
t7
DB10 DB2
t5
DB1 DB0
t8
ADD1 DOUT THREE- ADD2 t9 STATE DIN WRITE REG SEL1
ADD0
SIGN
tQUIET
t10
REG SEL2 MSB LSB DON'T CARE
THREE-STATE
04852-002
Figure 2. Serial Interface Timing Diagram
Rev. A | Page 6 of 36
AD7328 ABSOLUTE MAXIMUM RATINGS
TA = 25C, unless otherwise noted Table 4.
Parameter VDD to AGND, DGND VSS to AGND, DGND VDD to VCC VCC to AGND, DGND VDRIVE to AGND, DGND AGND to DGND Analog Input Voltage to AGND1 Digital Input Voltage to DGND Digital Output Voltage to GND REFIN to AGND Input Current to Any Pin Except Supplies2 Operating Temperature Range Storage Temperature Range Junction Temperature TSSOP Package JA Thermal Impedance JC Thermal Impedance Pb-Free Temperature, Soldering Reflow ESD
1
Rating -0.3 V to +16.5 V +0.3 V to -16.5 V VCC - 0.3 V to +16.5 V -0.3 V to +7 V -0.3 V to +7 V -0.3 V to +0.3 V VSS - 0.3 V to VDD + 0.3 V -0.3 V to +7 V -0.3 V to VDRIVE + 0.3 V -0.3 V to VCC + 0.3 V 10 mA -40C to +85C -65C to +150C 150C 143C/W 45C/W 260(0)C 2.5 kV
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
If the analog inputs are driven from alternative VDD and VSS supply circuitry, Schottky diodes should be placed in series with the AD7328's VDD and VSS supplies. 2 Transient currents of up to 100 mA do not cause SCR latch-up.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. A | Page 7 of 36
AD7328 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
CS 1 DIN 2 DGND 3 AGND 4 REFIN/OUT 5 VSS 6 VIN0 7 VIN1 8 VIN4 9 VIN5 10
20 19
SCLK DGND DOUT VDRIVE VCC VDD VIN2 VIN3
04852-003
AD7328
TOP VIEW (Not to Scale)
18 17 16 15 14 13 12 11
VIN6 VIN7
Figure 3. TSSOP Pin Configuration
Table 5. Pin Function Descriptions
Pin No. 1 2 3, 19 Mnemonic CS DIN DGND Description Chip Select. Active low logic input. This input provides the dual function of initiating conversions on the AD7328 and frames the serial data transfer. Data In. Data to be written to the on-chip registers is provided on this input and is clocked into the register on the falling edge of SCLK (see the Registers section). Digital Ground. Ground reference point for all digital circuitry on the AD7328. The DGND and AGND voltages should ideally be at the same potential and must not be more than 0.3 V apart, even on a transient basis. Analog Ground. Ground reference point for all analog circuitry on the AD7328. All analog input signals and any external reference signal should be referred to this AGND voltage. The AGND and DGND voltages should ideally be at the same potential and must not be more than 0.3 V apart, even on a transient basis. Reference Input/Reference Output. The on-chip reference is available on this pin for use external to the AD7328. The nominal internal reference voltage is 2.5 V, which appears at the pin. A 680 nF capacitor should be placed on the reference pin. Alternatively, the internal reference can be disabled and an external reference applied to this input. On power-up, the external reference mode is the default condition (see the Reference section). Negative Power Supply Voltage. This is the negative supply voltage for the analog input section. Analog Input 0 to Analog Input 7. The analog inputs are multiplexed into the on-chip track-and-hold. The analog input channel for conversion is selected by programming the Channel Address Bit ADD2 through Bit ADD0 in the control register. The inputs can be configured as eight single-ended inputs, four true differential input pairs, four pseudo differential inputs, or seven pseudo differential inputs. The configuration of the analog inputs is selected by programming the mode bits, Bit Mode 1 and Bit Mode 0, in the control register. The input range on each input channel is controlled by programming the range registers. Input ranges of 10 V, 5 V, 2.5 V, and 0 V to +10 V can be selected on each analog input channel when a +2.5 V reference voltage is used (see the Reference section). Positive Power Supply Voltage. This is the positive supply voltage for the analog input section. Analog Supply Voltage, 2.7 V to 5.25 V. This is the supply voltage for the ADC core on the AD7328. This supply should be decoupled to AGND. Specifications apply from VCC = 4.75 V to 5.25 V. Logic Power Supply Input. The voltage supplied at this pin determines at what voltage the interface operates. This pin should be decoupled to DGND. The voltage at this pin may be different to that at VCC, but it should not exceed VCC by more than 0.3 V. Serial Data Output. The conversion output data is supplied to this pin as a serial data stream. The bits are clocked out on the falling edge of the SCLK input, and 16 SCLKs are required to access the data. The data stream consists of three channel identification bits, the sign bit, and 12 bits of conversion data. The data is provided MSB first (see the Serial Interface section). Serial Clock, Logic Input. A serial clock input provides the SCLK used for accessing the data from the AD7328. This clock is also used as the clock source for the conversion process.
4
AGND
5
REFIN/OUT
6 7, 8, 14, 13, 9, 10, 12, 11
VSS VIN0 to VIN7
15 16 17
VDD VCC VDRIVE
18
DOUT
20
SCLK
Rev. A | Page 8 of 36
AD7328 TYPICAL PERFORMANCE CHARACTERISTICS
0 -20 -40
SNR (dB)
1.0
4096 POINT FFT VCC = VDRIVE = 5V VDD, VSS = 15V TA = 25C INT/EXT 2.5V REFERENCE 10V RANGE FIN = 50kHz SNR = 77.30dB SINAD = 76.85dB THD = -86.96dB SFDR = -88.22dB
VCC = VDRIVE = 5V 0.8 TA = 25C VDD, VSS = 15V 0.6 0.4
INL ERROR (LSB)
INT/EXT 2.5V REFERENCE 10V RANGE +INL = +0.55LSB -INL = -0.68LSB
-60 -80 -100 -120 -140
0.2 0 -0.2 -0.4 -0.6
04852-004
-0.8 -1.0 0
0
50
100
150
200
250
300
350
400
450
500
FREQUENCY (kHz)
8192 1024 2048 3072 4096 5120 6144 7168 512 1536 2560 3584 4608 5632 6656 7680 CODE
Figure 4. FFT True Differential Mode
Figure 7. Typical INL True Differential Mode
0 -20 -40
SNR (dB)
1.0
4096 POINT FFT VCC = VDRIVE = 5V VDD, VSS = 15V TA = 25C INT/EXT 2.5V REFERENCE 10V RANGE FIN = 50kHz SNR = 74.67dB SINAD = 74.03dB THD = -82.68dB SFDR = -85.40dB
0.8 0.6
DNL ERROR (LSB)
0.4 0.2 0 -0.2 -0.4 -0.6 VCC = VDRIVE = 5V 10V RANGE TA = 25C +DNL = +0.79LSB -DNL = -0.38LSB VDD, VSS = 15V INT/EXT 2.5V REFERENCE 0
-60 -80 -100 -120 -140
04852-005
-0.8 -1.0
0
50
100
150
200
250
300
350
400
450
500
FREQUENCY (kHz)
8192 1024 2048 3072 4096 5120 6144 7168 512 1536 2560 3584 4608 5632 6656 7680 CODE
Figure 5. FFT Single-Ended Mode
Figure 8. Typical DNL Single-Ended Mode
1.0 0.8 0.6
DNL ERROR (LSB)
1.0 0.8 0.6 0.4
INL ERROR (LSB)
0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 VCC = VDRIVE = 5V TA = 25C VDD, VSS = 15V INT/EXT 2.5V REFERENCE 10V RANGE +DNL = +0.72LSB -DNL = -0.22LSB
0.2 0 -0.2 VCC = VDRIVE = 5V TA = 25C VDD, VSS = 15V -0.6 INT/EXT 2.5V REFERENCE 10V RANGE -0.8 +INL = +0.87LSB -INL = -0.49LSB -1.0 0 8192 1024 2048 3072 4096 5120 6144 7168 512 1536 2560 3584 4608 5632 6656 7680 CODE -0.4
04852-006
8192 1024 2048 3072 4096 5120 6144 7168 512 1536 2560 3584 4608 5632 6656 7680 CODE
Figure 6. Typical DNL True Differential Mode
Rev. A | Page 9 of 36
Figure 9. Typical INL Single-Ended Mode
04852-044
04852-043
04852-007
AD7328
-50 -55 -60 -65
THD (dB)
80
VCC = 5V VDD/VSS = 12V TA = 25C fS = 1MSPS
10V DIFF 5V DIFF 75 2.5V DIFF
10V SE 0V TO +10V SE 0V TO +10V DIFF
SINAD (dB)
-70 -75 -80 -85 10V DIFF
5V SE 5V DIFF 2.5V DIFF
70
0V TO +10V SE 2.5V SE
65
10V SE
5V SE
0V TO +10V DIFF 60
2.5V SE -90
04852-008
55
-95 -100 10 100 ANALOG INPUT FREQUENCY (kHz)
1000
50 10
100 ANALOG INPUT FREQUENCY (kHz)
1000
Figure 10. THD vs. Analog Input Frequency for Single-Ended (SE) and True Differential Mode (Diff) at 5 V VCC
Figure 13. SINAD vs. Analog Input Frequency for Single-Ended (SE) and Differential Mode (Diff) at 3 V VCC
-50
-50
CHANNEL-TO-CHANNEL ISOLATION (dB)
-55 -60 -65
VCC = 3V VDD/VSS = 12V TA = 25C fS = 1MSPS
-55 -60 -65 -70 -75 -80 -85 -90 -95 VDD/VSS = 12V SINGLE-ENDED MODE fS = 1MSPS TA = 25C 50kHz ON SELECTED CHANNEL 0 100 200 300 400 500 VCC = 3V VCC = 5V
10V SE 0V TO +10V DIFF 5V SE
THD (dB)
-70 -75 -80 -85 -90 -95 -100 10 10V DIFF
0V TO +10V SE
2.5V SE 5V DIFF
04852-009
2.5V DIFF 100 ANALOG INPUT FREQUENCY (kHz)
1000
600
FREQUENCY OF INPUT NOISE (kHz)
Figure 11. THD vs. Analog Input Frequency for Single-Ended (SE) and True Differential Mode (Diff) at 3 V VCC
Figure 14. Channel-to-Channel Isolation
80 10V DIFF 75 5V DIFF 2.5V DIFF
10k 9k
9469
NUMBER OF OCCURRENCES
8k 7k 6k 5k 4k 3k 2k 1k 0 0 -2 228 -1 0 CODE
VCC = 5V VDD/VSS = 12V RANGE = 10V 10k SAMPLES TA = 25C
70
SINAD (dB)
0V TO +10V SE 65 10V SE
2.5V SE 5V SE
0V TO +10V DIFF 60 VCC = 5V VDD/VSS = 12V TA = 25C fS = 1MSPS 100 ANALOG INPUT FREQUENCY (kHz)
55
04852-010
303 1
50 10
0 2
1000
Figure 12. SINAD vs. Analog Input Frequency for Single-Ended (SE) and Differential Mode (Diff) at 5 V VCC
Figure 15. Histogram of Codes, True Differential Mode
Rev. A | Page 10 of 36
04852-013
04852-012
04852-011
VCC = 3V VDD/VSS = 12V TA = 25C fS = 1MSPS
AD7328
8k 7k 7600
2.0
VCC = 5V VDD/VSS = 12V RANGE = 10V 10k SAMPLES TA = 25C
1.5 INL = 500kSPS 1.0
INL ERROR (LSB)
NUMBER OF OCCURRENCES
6k 5k 4k 3k 2k 1201 1k 0 0 -3 23 -2 -1 0 CODE 1 1165
INL = 750kSPS
0.5 0 INL = 500kSPS -0.5 -1.0 INL = 1MSPS INL = 750kSPS
04852-014
11 2
0 3
-2.0
5
7
9
11
13
15
17
19
VDD/VSS SUPPLY VOLTAGE (V)
Figure 16. Histogram of Codes, Single-Ended Mode
Figure 19. INL Error vs. Supply Voltage at 500 kSPS, 750 kSPS, and 1 MSPS
-50 -55 -60 -65
-50 -55 -60 -65 100mV p-p SINE WAVE ON EACH SUPPLY NO DECOUPLING SINGLE-ENDED MODE fS = 1MSPS VCC = 5V VCC = 3V
CMRR (dB)
PSRR (dB)
-70 -75 -80 -85 -90 -95 -100 0
VCC = 5V
-70 -75 -80 -85 -90
VDD = 12V
VCC = 3V DIFFERENTIAL MODE FIN = 50kHz VDD/VSS = 12V fS = 1MSPS TA = 25C 200 400 600 800 1000
VSS = -12V
04852-054
04852-055
-95 -100 0 200 400 600 800 1000
1200
1200
RIPPLE FREQUENCY (kHz)
SUPPLY RIPPLE FREQUENCY (kHz)
Figure 17. CMRR vs. Common-Mode Ripple Frequency
Figure 20. PSRR vs. Supply Ripple Frequency Without Supply Decoupling
2.0 DNL = 750kSPS 1.5 1.0
DNL ERROR (LSB)
-50 -55 -60 -65
DNL = 500kSPS
VCC = VDRIVE = 5V VDD/VSS = 12V TA = 25C INTERNAL REFERENCE RANGE = 10V AND 2.5V RIN = 2000, 10V RANGE
RIN = 100, 10V RANGE RIN = 50, 10V RANGE RIN = 4700, 2.5V RANGE RIN = 2000, 2.5V RANGE RIN = 1000, 2.5V RANGE RIN = 100, 2.5V RANGE RIN = 50, 2.5V RANGE 100
04852-015
0.5 0 -0.5 -1.0 -1.5 -2.0 DNL = 750kSPS 5V RANGE VCC = VDRIVE = 5V INTERNAL REFERENCE SINGLE-ENDED MODE 5 7 9 11 13 15 DNL = 1MSPS
THD (dB)
DNL = 1MSPS
-70 RIN = 1000, 10V RANGE -75 -80
DNL = 500kSPS
04852-049
-85 -90 -95 10
17
19
1000
VDD/VSS SUPPLY VOLTAGE (V)
ANALOG INPUT FREQUENCY (kHz)
Figure 18. DNL Error vs. Supply Voltage at 500 kSPS, 750 kSPS, and 1 MSPS
Figure 21. THD vs. Analog Input Frequency for Various Source Impedances, True Differential Mode
Rev. A | Page 11 of 36
04852-050
-1.5
INL = 1MSPS
5V RANGE VCC = VDRIVE = 5V INTERNAL REFERENCE SINGLE-ENDED MODE
AD7328
-50 -55 -60 -65 VCC = VDRIVE = 5V VDD/VSS = 12V TA = 25C INTERNAL REFERENCE RANGE = 10V AND 2.5V RIN = 2000, 10V RANGE RIN = 100, 10V RANGE RIN = 50, 10V RANGE RIN = 2000, 2.5V RANGE RIN = 1000, 2.5V RANGE RIN = 100, 2.5V RANGE RIN = 50, 2.5V RANGE 100 INPUT FREQUENCY (kHz)
04852-016
THD (dB)
-70 RIN = 1000, 10V RANGE -75 -80 -85 -90 -95 10
1000
Figure 22. THD vs. Analog Input Frequency for Various Source Impedances, Single-Ended Mode
Rev. A | Page 12 of 36
AD7328 TERMINOLOGY
Differential Nonlinearity This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Integral Nonlinearity This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale (a point 1 LSB below the first code transition) and full scale (a point 1 LSB above the last code transition). Offset Code Error This applies to straight binary output coding. It is the deviation of the first code transition (00 ... 000) to (00 ... 001) from the ideal, that is, AGND + 1 LSB. Offset Error Match This is the difference in offset error between any two input channels. Gain Error This applies to straight binary output coding. It is the deviation of the last code transition (111 ... 110) to (111 ... 111) from the ideal (that is, 4 x VREF - 1 LSB, 2 x VREF - 1 LSB, VREF - 1 LSB) after adjusting for the offset error. Gain Error Match This is the difference in gain error between any two input channels. Bipolar Zero Code Error This applies when using twos complement output coding and a bipolar analog input. It is the deviation of the midscale transition (all 1s to all 0s) from the ideal input voltage, that is, AGND - 1 LSB. Bipolar Zero Code Error Match This refers to the difference in bipolar zero code error between any two input channels. Positive Full-Scale Error This applies when using twos complement output coding and any of the bipolar analog input ranges. It is the deviation of the last code transition (011 ... 110) to (011 ... 111) from the ideal (4 x VREF - 1 LSB, 2 x VREF - 1 LSB, VREF - 1 LSB) after adjusting for the bipolar zero code error. Positive Full-Scale Error Match This is the difference in positive full-scale error between any two input channels. Negative Full-Scale Error This applies when using twos complement output coding and any of the bipolar analog input ranges. This is the deviation of the first code transition (10 ... 000) to (10 ... 001) from the ideal (that is, -4 x VREF + 1 LSB, -2 x VREF + 1 LSB, -VREF + 1 LSB) after adjusting for the bipolar zero code error. Negative Full-Scale Error Match This is the difference in negative full-scale error between any two input channels. Track-and-Hold Acquisition Time The track-and-hold amplifier returns into track mode after the 14th SCLK rising edge. Track-and-hold acquisition time is the time required for the output of the track-and-hold amplifier to reach its final value, within 1/2 LSB, after the end of a conversion. For the 2.5 V range, the specified acquisition time is the time required for the track-and-hold amplifier to settle to within 1 LSB. Signal to (Noise + Distortion) Ratio This is the measured ratio of signal to (noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent on the number of quantization levels in the digitization process. The more levels, the smaller the quantization noise. Theoretically, the signal to (noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by Signal to (Noise + Distortion) = (6.02 N + 1.76) dB For a 13-bit converter, this is 80.02 dB. Total Harmonic Distortion Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7328, it is defined as
THD(dB) = 20 log V2 2 + V3 2 + V 4 2 + V5 2 + V6 2 V1
where V1 is the rms amplitude of the fundamental, and V2, V3, V4, V5, and V6 are the rms amplitudes of the second through the sixth harmonics. Peak Harmonic or Spurious Noise Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2, excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the largest harmonic in the spectrum, but for ADCs where the harmonics are buried in the noise floor, the largest harmonic could be a noise peak.
Rev. A | Page 13 of 36
AD7328
Channel-to-Channel Isolation Channel-to-channel isolation is a measure of the level of crosstalk between any two channels. It is measured by applying a full-scale, 100 kHz sine wave signal to all unselected input channels and determining the degree to which the signal attenuates in the selected channel with a 50 kHz signal. Figure 14 shows the worstcase across all eight channels for the AD7328. The analog input range is programmed to be the same on all channels. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities creates distortion products at sum and difference frequencies of mfa nfb, where m, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms are those for which neither m nor n are equal to 0. For example, the second-order terms include (fa + fb) and (fa - fb), whereas the third-order terms include (2fa + fb), (2fa - fb), (fa + 2fb), and (fa - 2fb). The AD7328 is tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second-order terms are usually distanced in frequency from the original sine waves, whereas the third-order terms are usually at a frequency close to the input frequencies. As a result, the second- and third-order terms are specified separately. The calculation of the intermodulation distortion is per the THD specification, where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals expressed in decibels. PSR (Power Supply Rejection) Variations in power supply affect the full-scale transition but not the linearity of the converter. Power supply rejection is the maximum change in the full-scale transition point due to a change in power supply voltage from the nominal value (see the Typical Performance Characteristics section). Thermal Hysteresis Thermal hysteresis is defined as the absolute maximum change of reference output voltage after the device is cycled through temperature from either T_HYS+ = +25C to TMAX to +25C or T_HYS- = +25C to TMIN to +25C It is expressed in ppm using the following equation:
VHYS ( ppm) = VREF (25C ) - VREF (T _ HYS) x 10 6 VREF (25C )
where: VREF(25C) is VREF at 25C. VREF(T_HYS) is the maximum change of VREF at T_HYS+ or T_HYS-. CMRR (Common-Mode Rejection Ratio) CMRR is defined as the ratio of the power in the ADC output at full-scale frequency, f, to the power of a 100 mV sine wave applied to the common-mode voltage of the VIN+ and VIN- frequency, fS, as CMRR (dB) = 10 log (Pf/PfS) where Pf is the power at frequency f in the ADC output, and PfS is the power at frequency fS in the ADC output (see Figure 17).
Rev. A | Page 14 of 36
AD7328 THEORY OF OPERATION
CIRCUIT INFORMATION
The AD7328 is a fast, 8-channel, 12-bit plus sign, bipolar input, serial A/D converter. The AD7328 can accept bipolar input ranges that include 10 V, 5 V, and 2.5 V; it can also accept a 0 V to +10 V unipolar input range. A different analog input range can be programmed on each analog input channel via the on-chip registers. The AD7328 has a high speed serial interface that can operate at throughput rates up to 1 MSPS. The AD7328 requires VDD and VSS dual supplies for the high voltage analog input structures. These supplies must be equal to or greater than the analog input range. See Table 6 for the requirements of these supplies for each analog input range. The AD7328 requires a low voltage 2.7 V to 5.25 V VCC supply to power the ADC core. Table 6. Reference and Supply Requirements for Each Analog Input Range
Selected Analog Input Range (V) 10 5 2.5 0 to 10 Reference Voltage (V) 2.5 3.0 2.5 3.0 2.5 3.0 2.5 3.0 Full-Scale Input Range (V) 10 12 5 6 2.5 3 0 to +10 0 to +12 AVCC (V) 3/5 3/5 3/5 3/5 3/5 3/5 3/5 3/5 Minimum VDD/VSS (V) 10 12 5 6 5 5 +10/AGND +12/AGND
The analog inputs can be configured as eight single-ended inputs, four true differential input pairs, four pseudo differential inputs, or seven pseudo differential inputs. Selection can be made by programming the mode bits, Mode 0 and Mode 1, in the control register. The serial clock input accesses data from the part and provides the clock source for the successive approximation ADC. The AD7328 has an on-chip 2.5 V reference. However, the AD7328 can also work with an external reference. On power-up, the external reference operation is the default option. If the internal reference is the preferred option, the user must write to the reference bit in the control register to select the internal reference operation. The AD7328 also features power-down options to allow power savings between conversions. The power-down modes are selected by programming the on-chip control register as described in the Modes of Operation section.
CONVERTER OPERATION
The AD7328 is a successive approximation analog-to-digital converter built around two capacitive DACs. Figure 23 and Figure 24 show simplified schematics of the ADC in singleended mode during the acquisition and conversion phases, respectively. Figure 25 and Figure 26 show simplified schematics of the ADC in differential mode during acquisition and conversion phases, respectively. The ADC is composed of control logic, a SAR, and capacitive DACs. In Figure 23 (the acquisition phase), SW2 is closed and SW1 is in Position A, the comparator is held in a balanced condition, and the sampling capacitor array acquires the signal on the input.
CAPACITIVE DAC B CS SW2 COMPARATOR CONTROL LOGIC
AGND
Figure 31 shows the change in THD as the VDD and VSS supplies are reduced. At the maximum throughput rate, the THD degrades significantly as VDD and VSS are reduced. It is therefore necessary to reduce the throughput rate when using minimum VDD and VSS supplies so that there is less degradation of THD and the specified performance can be maintained. The degradation is due to an increase in the on resistance of the input multiplexer when the VDD and VSS supplies are reduced.
Figure 23. ADC Acquisition Phase (Single Ended)
When the ADC starts a conversion (Figure 24), SW2 opens and SW1 moves to Position B, causing the comparator to become unbalanced. The control logic and the charge redistribution DAC are used to add and subtract fixed amounts of charge from the capacitive DAC to bring the comparator back into a balanced condition. When the comparator is rebalanced, the conversion is complete. The control logic generates the ADC output code.
Rev. A | Page 15 of 36
04852-017
To meet the specified performance specifications when the AD7328 is configured with the minimum VDD and VSS supplies for a chosen analog input range, the throughput rate should be decreased from the maximum throughput range (see the Typical Performance Characteristics section). Figure 18 and Figure 19 show the change in INL and DNL as the VDD and VSS voltages are varied. When operating at the maximum throughput rate, as the VDD and VSS supply voltages are reduced, the INL and DNL error increases. However, as the throughput rate is reduced with the minimum VDD and VSS supplies, the INL and DNL error is reduced.
VIN0
A SW1
AD7328
CAPACITIVE DAC B CS SW2 COMPARATOR CONTROL LOGIC
VIN0
A SW1 AGND
The ideal transfer characteristic for the AD7328 when twos complement coding is selected is shown in Figure 27. The ideal transfer characteristic for the AD7328 when straight binary coding is selected is shown in Figure 28.
04852-018
Figure 24. ADC Conversion Phase (Single-Ended)
011...111 011...110
CAPACITIVE DAC B CS SW3 COMPARATOR CONTROL LOGIC
Figure 27. Twos Complement Transfer Characteristic (Bipolar Ranges)
VIN+ VIN-
A SW1 A SW2 B VREF CS
111...111 111...110
ADC CODE
111...000 011...111
CAPACITIVE DAC
Figure 25. ADC Differential Configuration During Acquisition Phase
CAPACITIVE DAC B CS SW3 COMPARATOR CONTROL LOGIC
04852-019
000...010 000...001 000...000
04852-022
-FSR/2 + 1LSB +FSR/2 - 1LSB BIPOLAR RANGES AGND + 1LSB +FSR - 1LSB UNIPOLAR RANGE ANALOG INPUT
VIN+ VIN-
A SW1 A SW2 B VREF CS
Figure 28. Straight Binary Transfer Characteristic (Bipolar Ranges)
ANALOG INPUT STRUCTURE
The analog inputs of the AD7328 can be configured as singleended, true differential, or pseudo differential via the control register mode bits (see Table 10). The AD7328 can accept true bipolar input signals. On power-up, the analog inputs operate as eight single-ended analog input channels. If true differential or pseudo differential is required, a write to the control register is necessary after power-up to change this configuration. Figure 29 shows the equivalent analog input circuit of the AD7328 in single-ended mode. Figure 30 shows the equivalent analog input structure in differential mode. The two diodes provide ESD protection for the analog inputs.
VDD D VIN0 C1 D VSS R1 C2
04852-020
CAPACITIVE DAC
Figure 26. ADC Differential Configuration During Conversion Phase
Output Coding
The AD7328 default output coding is set to twos complement. The output coding is controlled by the coding bit in the control register. To change the output coding to straight binary coding, the coding bit in the control register must be set. When operating in sequence mode, the output coding for each channel in the sequence is the value written to the coding bit during the last write to the control register.
Transfer Functions
The designed code transitions occur at successive integer LSB values (that is, 1 LSB, 2 LSB, and so on). The LSB size is dependent on the analog input range selected. Table 7. LSB Sizes for Each Analog Input Range
Input Range 10 V 5 V 2.5 V 0 V to +10 V Full-Scale Range/8192 Codes 20 V 10 V 5V 10 V LSB Size 2.441 mV 1.22 mV 0.61 mV 1.22 mV
Figure 29. Equivalent Analog Input Circuit (Single-Ended)
Rev. A | Page 16 of 36
04852-023
04852-021
Figure 25 shows the differential configuration during the acquisition phase. For the conversion phase, SW3 opens and SW1 and SW2 move to Position B (see Figure 26). The output impedances of the source driving the VIN+ and VIN- pins must match; otherwise, the two inputs have different settling times, resulting in errors.
ADC CODE
000...001 000...000 111...111
100...010 100...001 100...000 -FSR/2 + 1LSB AGND + 1LSB AGND - 1LSB +FSR/2 - 1LSB BIPOLAR RANGES +FSR - 1LSB UNIPOLAR RANGE ANALOG INPUT
AD7328
VDD D VIN+ C1 D VSS VDD D VIN- C1 D VSS R1 C2 R1 C2
The AD7328 enters track mode on the 14th SCLK rising edge. When the AD7328 is run at a throughput rate of 1 MSPS with a 20 MHz SCLK signal, the ADC has approximately 1.5 SCLK + t8 + tQUIET to acquire the analog input signal. The ADC goes back into hold mode on the CS falling edge. As the VDD/VSS supply voltage is reduced, the on-resistance of the input multiplexer increases. Therefore, based on the equation for tACQ, it is necessary to increase the acquisition time provided to the AD7328 and hence decrease the overall throughput rate. Figure 31 shows that if the throughput rate is reduced when operating with minimum VDD and VSS supplies, the specified THD performance is maintained.
-50 -55 -60 -65
THD (dB)
Figure 30. Equivalent Analog Input Circuit (Differential)
Care should be taken to ensure that the analog input does not exceed the VDD and VSS supply rails by more than 300 mV. Exceeding this value causes the diodes to become forward biased and to start conducting into either the VDD supply rail or VSS supply rail. These diodes can conduct up to 10 mA without causing irreversible damage to the part. In Figure 29 and Figure 30, Capacitor C1 is typically 4 pF and can primarily be attributed to pin capacitance. Resistor R1 is a lumped component made up of the on-resistance of the input multiplexer and the track-and-hold switch. Capacitor C2 is the sampling capacitor; its capacitance varies depending on the analog input range selected (see the Specifications section).
04852-024
VCC = VDRIVE = 5V INTERNAL REFERENCE TA = 25C FIN = 10kHz 5V RANGE SE MODE
-70 -75 -80 -85 -90 500kSPS -95 5 7 9 11 13 15 17 19 750kSPS
04852-051
1MSPS
Track-and-Hold Section
The track-and-hold on the analog input of the AD7328 allows the ADC to accurately convert an input sine wave of full-scale amplitude to 13-bit accuracy. The input bandwidth of the trackand-hold is greater than the Nyquist rate of the ADC. The AD7328 can handle frequencies up to 22 MHz. The track-and-hold enters its tracking mode on the 14th SCLK rising edge after the CS falling edge. The time required to acquire an input signal depends on how quickly the sampling capacitor is charged. With zero source impedance, 305 ns is sufficient to acquire the signal to the 13-bit level. The acquisition time for the 10 V, 5 V, and 0 V to +10 V ranges to settle to within 1/2 LSB is typically 200 ns. The acquisition time required is calculated using the following formula: tACQ = 10 x ((RSOURCE + R) C) where C is the sampling capacitance, and R is the resistance seen by the track-and-hold amplifier looking at the input. For the AD7328, the value of R includes the on-resistance of the input multiplexer and is typically 300 . RSOURCE should include any extra source impedance on the analog input.
VDD/VSS SUPPLIES (V)
Figure 31. THD vs. VDD/VSS Supply Voltage at 500 kSPS, 750 kSPS, and 1 MSPS
Unlike other bipolar ADCs, the AD7328 does not have a resistive analog input structure. On the AD7328, the bipolar analog signal is sampled directly onto the sampling capacitor. This gives the AD7328 high analog input impedance. The analog input impedance can be calculated from the following formula: Z = 1/(fS x CS) where fS is the sampling frequency, and CS is the sampling capacitor value. CS depends on the analog input range chosen (see the Specifications section). When operating at 1 MSPS, the analog input impedance is typically 75 k for the 10 V range. As the sampling frequency is reduced, the analog input impedance further increases. As the analog input impedance increases, the current required to drive the analog input therefore decreases.
Rev. A | Page 17 of 36
AD7328
TYPICAL CONNECTION DIAGRAM
Figure 32 shows a typical connection diagram for the AD7328. In this configuration, the AGND pin is connected to the analog ground plane of the system, and the DGND pin is connected to the digital ground plane of the system. The analog inputs on the AD7328 can be configured to operate in single-ended, true differential, or pseudo differential mode. The AD7328 can operate with either an internal or external reference. In Figure 32, the AD7328 is configured to operate with the internal 2.5 V reference. A 680 nF decoupling capacitor is required when operating with the internal reference. The VCC pin can be connected to either a 3 V or 5 V supply voltage. The VDD and VSS are the dual supplies for the high voltage analog input structures. The voltage on these pins must be equal to or greater than the highest analog input range selected on the analog input channels (see Table 6 for more information). The VDRIVE pin is connected to the supply voltage of the microprocessor. The voltage applied to the VDRIVE input controls the voltage of the serial interface. VDRIVE can be set to 3 V or 5 V.
+15V 0.1F + 10F 10F + 0.1F VCC +2.7V TO +5.25V
V+
5V
AGND
VIN+
VDD VCC
AD73281
VSS
1ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 33. Single-Ended Mode Typical Connection Diagram
True Differential Mode
The AD7328 can have four true differential analog input pairs. Differential signals have some benefits over single-ended signals, including better noise immunity based on the device's common-mode rejection and improvements in distortion performance. Figure 34 defines the configuration of the true differential analog inputs of the AD7328.
VIN+
AD73281
VIN-
04852-027
VDD1
VCC VDRIVE 10F + 0.1F
+3V SUPPLY
1ADDITIONAL PINS OMITTED FOR CLARITY.
ANALOG INPUTS 10V, 5V, 2.5V 0V TO +10V
VIN0 VIN1 VIN2 VIN3 VIN4 VIN5 VIN6 VIN7
AD7328
CS DOUT SCLK DIN C/P
Figure 34. True Differential Inputs
DGND
680nF
REFIN/OUT VSS1 AGND
SERIAL INTERFACE
-15V
04852-025
0.1F
+
10F
1MINIMUM
VDD AND VSS SUPPLY VOLTAGES DEPEND ON THE HIGHEST ANALOG INPUT RANGE SELECTED.
The amplitude of the differential signal is the difference between the signals applied to the VIN+ and VIN- pins in each differential pair (VIN+ - VIN-). VIN+ and VIN- should be simultaneously driven by two signals of equal amplitude, dependent on the input range selected, that are 180 out of phase. Assuming the 4 x VREF mode, the amplitude of the differential signal is -20 V to +20 V p-p (2 x 4 x VREF), regardless of the common mode. The common mode is the average of the two signals (VIN+ + VIN-)/2 and is therefore the voltage on which the two input signals are centered. This voltage is set up externally, and its range varies with reference voltage. As the reference voltage increases, the common-mode range decreases. When driving the differential inputs with an amplifier, the actual common-mode range is determined by the amplifier's output swing. If the differential inputs are not driven from an amplifier, the common-mode range is determined by the supply voltage on the VDD supply pin and the VSS supply pin. When a conversion takes place, the common mode is rejected, resulting in a noise-free signal of amplitude -2 x (4 x VREF) to +2 x (4 x VREF), corresponding to Digital Codes -4096 to +4095.
Figure 32. Typical Connection Diagram
ANALOG INPUT
Single-Ended Inputs
The AD7328 has a total of eight analog inputs when operating in single-ended mode. Each analog input can be independently programmed to one of the four analog input ranges. In applications where the signal source is high impedance, it is recommended to buffer the signal before applying it to the ADC analog inputs. Figure 33 shows the configuration of the AD7328 in singleended mode.
Rev. A | Page 18 of 36
04852-026
V-
AD7328
5 4 3 2
VCOM RANGE (V)
8
5V RANGE 2.5V RANGE 5V RANGE
6 4
VCOM RANGE (V)
10V RANGE
2.5V RANGE
5V RANGE
1 0 -1 -2 -3 -4
04852-045
2 0 -2 -4 -6 -8
10V RANGE
10V RANGE 10V RANGE
2.5V RANGE
5V RANGE VCC = 5V VREF = 2.5V 16.5V VDD/VSS 12V VDD/VSS 2.5V RANGE
04852-048
-5 -6
VCC = 3V VREF = 3V 16.5V VDD/VSS 12V VDD/VSS
Figure 35. Common-Mode Range for VCC = 3 V and REFIN/OUT = 3 V
8 5V RANGE 2.5V RANGE 5V RANGE 2.5V RANGE
Figure 38. Common-Mode Range for VCC = 5 V and REFIN/OUT = 2.5 V
Pseudo Differential Inputs
The AD7328 can have four pseudo differential pairs or seven pseudo differential inputs referenced to a common VIN- pin. The VIN+ inputs are coupled to the signal source and must have an amplitude within the selected range for that channel as programmed in the range register. A dc input is applied to the VIN- pin. The voltage applied to this input provides an offset for the VIN+ input from ground or a pseudo ground. Pseudo differential inputs separate the analog input signal ground from the ADC ground, allowing cancellation of dc common-mode voltages. Figure 39 shows the configuration of the AD7328 in pseudo differential mode. When a conversion takes place, the pseudo ground corresponds to Code -4096, and the maximum amplitude corresponds to Code +4095.
V+
5V RANGE 5V RANGE
6
VCOM RANGE (V)
4
10V RANGE
2 10V RANGE 0
-2
04852-046
VCC = 5V VREF = 3V -4 16.5V VDD/VSS 12V VDD/VSS
Figure 36. Common-Mode Range for VCC = 5 V and REFIN/OUT = 3 V
6 4 2
VCOM RANGE (V)
5V
VIN+
0 -2 -4 -6 -8 16.5V VDD/VSS 12V VDD/VSS 10V RANGE
VDD VCC
AD73281
10V 2.5V RANGE RANGE
VIN-
2.5V RANGE
VSS
VCC = 3V VREF = 2.5V
04852-047
1ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 39. Pseudo Differential Inputs
Figure 37. Common-Mode Range for VCC = 3 V and REFIN/OUT = 2.5 V
Figure 40 and Figure 41 show the typical voltage range on the VIN- pin for various analog input ranges when configured in the pseudo differential mode. For example, when the AD7328 is configured to operate in pseudo differential mode and the 5 V range is selected with 16.5 V VDD/VSS supplies and 5 V VCC, the voltage on the VIN- pin can vary from -6.5 V to +6.5 V.
Rev. A | Page 19 of 36
04852-028
V-
AD7328
8 6 4 2 0 -2 -4 -6 -8 VCC = 5V VREF = 2.5V 5V RANGE 2.5V RANGE 10V RANGE 5V RANGE 2.5V RANGE
10V RANGE
The driver amplifier must be able to settle for a full-scale step to a 13-bit level, 0.0122%, in less than the specified acquisition time of the AD7328. An op amp such as the AD8021 meets this requirement when operating in single-ended mode. The AD8021 needs an external compensating NPO type of capacitor. The AD8022 can also be used in high frequency applications where a dual version is required. For lower frequency applications, op amps such as the AD797, AD845, and AD8610 can be used with the AD7328 in single-ended mode configuration. Differential operation requires that VIN+ and VIN- be simultaneously driven with two signals of equal amplitude that are 180 out of phase. The common mode must be set up externally to the AD7328. The common-mode range is determined by the REFIN/OUT voltage, the VCC supply voltage, and the particular amplifier used to drive the analog inputs. Differential mode with either an ac input or a dc input provides the best THD performance over a wide frequency range. Because not all applications have a signal preconditioned for differential operation, there is often a need to perform a single-ended-to-differential conversion. This single-ended-to-differential conversion can be performed using an op amp pair. Typical connection diagrams for an op amp pair are shown in Figure 42 and Figure 43. In Figure 42, the common-mode signal is applied to the noninverting input of the second amplifier.
1.5k 2k V+
04852-039
04852-040
0V TO +10V RANGE
0V TO +10V RANGE
16.5V VDD/VSS
12V VDD/VSS
Figure 40. Pseudo Input Range with VCC = 5 V
4 5V RANGE 2 5V RANGE 2.5V RANGE
0
-2 2.5V RANGE
10V RANGE
-4
10V RANGE
-6 VCC = 3V VREF = 2.5V -8
0V TO +10V RANGE
0V TO +10V RANGE
16.5V VDD/VSS
12V VDD/VSS
VIN
Figure 41. Pseudo Input Range with VCC = 3 V
DRIVER AMPLIFIER CHOICE
In applications where the harmonic distortion and signal-tonoise ratio are critical specifications, the analog input of the AD7328 should be driven from a low impedance source. Large source impedances significantly affect the ac performance of the ADC and can necessitate the use of an input buffer amplifier. When no amplifier is used to drive the analog input, the source impedance should be limited to low values. The maximum source impedance depends on the amount of THD that can be tolerated in the application. The THD increases as the source impedance increases and performance degrades. Figure 21 and Figure 22 show graphs of the THD vs. the analog input frequency for various source impedances. Depending on the input range and analog input configuration selected, the AD7328 can handle source impedances of up to 4.7 k before the THD starts to degrade. Due to the programmable nature of the analog inputs on the AD7328, the choice of op amp used to drive the inputs is a function of the particular application and depends on the input configuration and the analog input voltage ranges selected.
1.5k
1.5k
1.5k
1.5k
V-
10k
Figure 42. Single-Ended-to-Differential Configuration with the AD845
442 442
VIN
AD8021
V+
442 442 442 442
V-
100
Figure 43. Single-Ended-to-Differential Configuration with the AD8021
Rev. A | Page 20 of 36
04852-030
AD8021
04852-029
AD7328 REGISTERS
The AD7328 has four programmable registers: the control register, sequence register, Range Register 1, and Range Register 2. These registers are write-only registers.
ADDRESSING REGISTERS
A serial transfer on the AD7328 consists of 16 SCLK cycles. The three MSBs on the DIN line during the 16 SCLK transfer are decoded to determine which register is addressed. The three MSBs consist of the write bit, Register Select 1 bit, and Register Select 2 bit. The register select bits are used to determine which of the four on-board registers is selected. The write bit determines if the data on the DIN line following the register select bits loads into the addressed register. If the write bit is 1, the bits load into the register addressed by the register select bits. If the write bit is 0, the data on the DIN line does not load into any register. Table 8. Decoding Register Select Bits and Write Bit
Write 0 1 1 1 1 Register Select 1 0 0 0 1 1 Register Select 2 0 0 1 0 1 Description Data on the DIN line during this serial transfer is ignored. This combination selects the control register. The subsequent 12 bits are loaded into the control register. This combination selects Range Register 1. The subsequent 8 bits are loaded into Range Register 1. This combination selects Range Register 2. The subsequent 8 bits are loaded into Range Register 2. This combination selects the sequence register. The subsequent 8 bits are loaded into the sequence register.
Rev. A | Page 21 of 36
AD7328
CONTROL REGISTER
The control register is used to select the analog input channel, analog input configuration, reference, coding, and power mode. The control register is a write-only, 12-bit register. Data loaded on the DIN line corresponds to the AD7328 configuration for the next conversion. If the sequence register is being used, data should be loaded into the control register after the range registers and the sequence register have been initialized. The bit functions of the control register are shown in Table 9 (the power-up status of all bits is 0).
MSB 15 Write 14 Register Select 1 13 Register Select 2 12 ADD2 11 ADD1 10 ADD0 9 Mode 1 8 Mode 0 7 PM1 6 PM0 5 Coding 4 Ref 3 Seq1 2 Seq2 1 Weak/ Three-State LSB 0 0
Table 9. Control Register Details
Bit 12, 11, 10 Mnemonic ADD2, ADD1, ADD0 Mode 1, Mode 0 Description These three channel address bits are used to select the analog input channel for the next conversion if the sequencer is not being used. If the sequencer is being used, the three channel address bits are used to select the final channel in a consecutive sequence. These two mode bits are used to select the configuration of the eight analog input pins, VIN0 to VIN7. These pins are used in conjunction with the channel address bits. On the AD7328, the analog inputs can be configured as eight single-ended inputs, four fully differential input pairs, four pseudo differential inputs, or seven pseudo differential inputs (see Table 10). The power management bits are used to select different power mode options on the AD7328 (see Table 11). This bit is used to select the type of output coding the AD7328 uses for the next conversion result. If the coding = 0, the output coding is twos complement. If the coding = 1, the output coding is straight binary. When operating in sequence mode, the output coding for each channel is the value written to the coding bit during the last write to the control register. The reference bit is used to enable or disable the internal reference. If Ref = 0, the external reference is enabled and used for the next conversion, and the internal reference is disabled. If Ref = 1, the internal reference is used for the next conversion. When operating in sequence mode, the reference used for each channel is the value written to the Ref bit during the last write to the control register. The Sequence 1 and Sequence 2 bits are used to control the operation of the sequencer (see Table 12). This bit selects the state of the DOUT line at the end of the current serial transfer. If the bit is set to 1, the DOUT line is weakly driven to Channel Address Bit ADD2 of the following conversion. If this bit is set to 0, DOUT returns to three-state at the end of the serial transfer (see the Serial Interface section).
9, 8
7, 6 5
PM1, PM0 Coding
4
Ref
3, 2 1
Seq1/Seq2 Weak/Three-State
The eight analog input channels can be configured as seven pseudo differential analog inputs, four pseudo differential inputs, four true differential input pairs, or eight single-ended analog inputs. Table 10. Analog Input Configuration Selection
Channel Address Bits ADD2 ADD1 ADD0 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 Mode 1 = 1, Mode 0 = 1 7 Pseudo Differential I/Ps VIN+ VIN- VIN0 VIN7 VIN1 VIN7 VIN2 VIN7 VIN3 VIN7 VIN4 VIN7 VIN5 VIN7 VIN6 VIN7 Temperature indicator Mode 1 = 1, Mode 0 = 0 4 Fully Differential I/Ps VIN+ VIN- VIN0 VIN1 VIN0 VIN1 VIN2 VIN3 VIN2 VIN3 VIN4 VIN5 VIN4 VIN5 VIN6 VIN7 VIN6 VIN7 Mode 1 = 0, Mode 0 = 1 4 Pseudo Differential I/Ps VIN+ VIN- VIN0 VIN1 VIN0 VIN1 VIN2 VIN3 VIN2 VIN3 VIN4 VIN5 VIN4 VIN5 VIN6 VIN7 VIN6 VIN7 Mode 1 = 0, Mode 0 = 0 8 Single-Ended I/Ps VIN+ VIN- VIN0 AGND VIN1 AGND VIN2 AGND VIN3 AGND VIN4 AGND VIN5 AGND VIN6 AGND VIN7 AGND
Rev. A | Page 22 of 36
AD7328
Table 11. Power Mode Selection
PM1 1 1 0 0 PM0 1 0 1 0 Description Full Shutdown Mode. In this mode, all internal circuitry on the AD7328 is powered down. Information in the control register is retained when the AD7328 is in full shutdown mode. Autoshutdown Mode. The AD7328 enters autoshutdown on the 15th SCLK rising edge when the control register is updated. All internal circuitry is powered down in autoshutdown. Autostandby Mode. In this mode, all internal circuitry is powered down, excluding the internal reference. The AD7328 enters autostandby mode on the 15th SCLK rising edge after the control register is updated. Normal Mode. All internal circuitry is powered up at all times.
Table 12. Sequencer Selection
Seq1 0 0 Seq2 0 1 Description The channel sequencer is not used. The analog channel, selected by programming the ADD2 to ADD0 bits in the control register, selects the next channel for conversion. Uses the sequence of channels that were previously programmed in the sequence register for conversion. The AD7328 starts converting on the lowest channel in the sequence. The channels are converted in ascending order. If uninterrupted, the AD7328 keeps converting the sequence. The range for each channel defaults to the range previously written into the corresponding range register. This configuration is used in conjunction with the channel address bits in the control register. This allows continuous conversions on a consecutive sequence of channels, from Channel 0 through a final channel selected by the channel address bits in the control register. The range for each channel defaults to the range previously written into the corresponding range register. The channel sequencer is not used. The analog channel, selected by programming the ADD2 bit to ADD0 bit in the control register, selects the next channel for conversion.
1
0
1
1
Rev. A | Page 23 of 36
AD7328
SEQUENCE REGISTER
The sequence register on the AD7328 is an 8-bit, write-only register. Each of the eight analog input channels has one corresponding bit in the sequence register. To select a channel for inclusion in the sequence, set the corresponding channel bit to 1 in the sequence register.
MSB 16 Write 15 Register Select 1 14 Register Select 2 13 VIN0 12 VIN1 11 VIN2 10 VIN3 9 VIN4 8 VIN5 7 VIN6 6 VIN7 5 0 4 0 3 0 2 0 LSB 1 0
RANGE REGISTERS
The range registers are used to select one analog input range per analog input channel. Range Register 1 is used to set the ranges for Channel 0 to Channel 3. It is an 8-bit, write-only register with two dedicated range bits for each of the analog input channels from Channel 0 to Channel 3. There are four analog input ranges, 10 V, 5 V, 2.5 V, and 0 V to +10 V. A write to Range Register 1 is selected by setting the write bit to 1 and the range select bits to 0 and 1. After the initial write to Range Register 1 occurs, each time an analog input is selected, the AD7328 automatically configures the analog input to the appropriate range, as indicated by Range Register 1. The 10 V input range is selected by default on each analog input channel (see Table 13).
MSB 16 Write 15 Register Select 1 14 Register Select 2 13 VIN0A 12 VIN0B 11 VIN1A 10 VIN1B 9 VIN2A 8 VIN2B 7 VIN3A 6 VIN3B 5 0 4 0 3 0 2 0 LSB 1 0
Range Register 2 is used to set the ranges for Channel 4 to Channel 7. It is an 8-bit, write-only register with two dedicated range bits for each of the analog input channels from Channel 4 to Channel 7. There are four analog input ranges, 10 V, 5 V, 2.5 V, and 0 V to +10 V. After the initial write to Range Register 2 occurs, each time an analog input is selected, the AD7328 automatically configures the analog input to the appropriate range, as indicated by Range Register 2. The 10 V input range is selected by default on each analog input channel (see Table 13).
MSB 16 Write 15 Register Select 1 14 Register Select 2 13 VIN4A 12 VIN4B 11 VIN5A 10 VIN5B 9 VIN6A 8 VIN6B 7 VIN7A 6 VIN7B 5 0 4 0 3 0 2 0 LSB 1 0
Table 13. Range Selection
VINxA 0 0 1 1 VINxB 0 1 0 1 Description This combination selects the 10 V input range on VINx. This combination selects the 5 V input range on VINx. This combination selects the 2.5 V input range on VINx. This combination selects the 0 V to +10 V input range on VINx.
Rev. A | Page 24 of 36
AD7328 SEQUENCER OPERATION
POWER ON. CS
DIN: WRITE TO RANGE REGISTER 1 TO SELECT THE RANGE FOR EACH ANALOG INPUT CHANNEL. DOUT: CONVERSION RESULT FROM CHANNEL 0, 10V RANGE, SINGLE-ENDED MODE. CS DIN: WRITE TO RANGE REGISTER 2 TO SELECT THE RANGE FOR EACH ANALOG INPUT CHANNEL. DOUT: CONVERSION RESULT FROM CHANNEL 0, SINGLE-ENDED MODE, RANGE SELECTED IN RANGE REGISTER 1. CS DIN: WRITE TO SEQUENCE REGISTER TO SELECT THE ANALOG INPUT CHANNELS TO BE INCLUDED IN THE SEQUENCE. DOUT: CONVERSION RESULT FROM CHANNEL 0, SINGLE-ENDED MODE, RANGE SELECTED IN RANGE REGISTER 1. CS DIN: WRITE TO CONTROL REGISTER TO START THE SEQUENCE, Seq1 = 0, Seq2 = 1. DOUT: CONVERSION RESULT FROM CHANNEL 0, SINGLE-ENDED MODE, RANGE SELECTED IN RANGE REGISTER 1. CS DIN: TIE DIN LOW/WRITE BIT = 0TO CONTINUE TO CONVERT THROUGH THE SEQUENCE OF CHANNELS. CS DIN: WRITE TO CONTROL REGISTER TO STOP THE SEQUENCE, Seq1 = 0, Seq2 = 0. DOUT: CONVERSION RESULT FROM CHANNEL IN SEQUENCE. DOUT: CONVERSION RESULT FROM FIRST CHANNEL IN THE SEQUENCE. DIN TIED LOW/WRITE BIT = 0.
STOPPING A SEQUENCE.
CONTINUOUSLY CONVERT ON THE SELECTED SEQUENCE OF CHANNELS.
SELECTING A NEW SEQUENCE. CS DIN: WRITE TO SEQUENCE REGISTER TO SELECT THE NEW SEQUENCE. DOUT: CONVERSION RESULT FROM CHANNEL X IN THE FIRST SEQUENCE.
04852-031
Figure 44. Programmable Sequence Flowchart
The AD7328 can be configured to automatically cycle through a number of selected channels using the on-chip sequence register with the Seq1 bit and the Seq2 bit in the control register. Figure 44 shows how to program the AD7328 register to operate in sequence mode. After power-up, all of the four on-chip registers contain default values. Each analog input has a default input range of 10 V. If different analog input ranges are required, a write to the range registers is necessary. This is shown in the first two serial transfers of Figure 44.
These two initial serial transfers are only necessary if input ranges other than the default ranges are required. After the analog input ranges are configured, a write to the sequence register is necessary to select the channels to be included in the sequence. Once the channels for the sequence have been selected, the sequence can be initiated by writing to the control register and setting Seq1 to 0 and Seq2 to 1. The AD7328 continues to convert the selected sequence without interruption provided that the sequence register remains unchanged and Seq1 = 0 and Seq2 = 1 in the control register.
Rev. A | Page 25 of 36
AD7328
If a write to one of the range registers is required during a sequence, it is necessary to first stop the sequence by writing to the control register and setting Seq1 to 0 and Seq2 to 0. Next, the write to the range register should be completed to change the required range. The previously selected sequence should then be initiated again by writing to the control register and setting Seq1 to 0 and Seq2 to 1. The ADC converts the first channel in the sequence. The AD7328 can be configured to convert a sequence of consecutive channels (see Figure 45). This sequence begins by converting on Channel 0 and ends with a final channel as selected by Bit ADD2 to Bit ADD0 in the control register. In this configuration, there is no need for a write to the sequence register. To operate the AD7328 in this mode, set Seq1 to 1 and Seq2 to 0 in the control register, and then select the final channel in the sequence by programming Bit ADD2 to Bit ADD0 in the control register.
POWER ON. CS DIN: WRITE TO RANGE REGISTER 1 TO SELECT THE RANGE FOR ANALOG INPUT CHANNELS. DOUT: CONVERSION RESULT FROM CHANNEL 0, 10V RANGE, SINGLE-ENDED MODE. CS DIN: WRITE TO RANGE REGISTER 2 TO SELECT THE RANGE FOR ANALOG INPUT CHANNELS. DOUT: CONVERSION RESULT FROM CHANNEL 0, RANGE SELECTED IN RANGE REGISTER 1, SINGLE-ENDED MODE. CS DIN: WRITE TO CONTROL REGISTER TO SELECT THE FINAL CHANNEL IN THE CONSECUTIVE SEQUENCE, SET Seq1 = 1 AND Seq2 = 0. SELECT OUTPUT CODING FOR SEQUENCE. DOUT: CONVERSION RESULT FROM CHANNEL 0, RANGE SELECTED IN RANGE REGISTER 1, SINGLE-ENDED MODE. CS DIN: WRITE BIT = 0 OR DIN LINE HELD LOW TO CONTINUE TO CONVERT THROUGH THE SEQUENCE OF CONSECUTIVE CHANNELS. DOUT: CONVERSION RESULT FROM CHANNEL 0, RANGE SELECTED IN RANGE REGISTER 1. CS DIN: WRITE BIT = 0 OR DIN LINE HELD LOW TO CONTINUE THROUGH SEQUENCE OF CONSECUTIVE CHANNELS. DOUT: CONVERSION RESULT FROM CHANNEL 1, RANGE SELECTED IN RANGE REGISTER 1. DIN TIED LOW/WRITE BIT = 0.
Once the control register is configured to operate the AD7328 in this mode, the DIN line can be held low or the write bit can be set to 0. To return to traditional multichannel operation, a write to the control register to set Seq1 to 0 and Seq2 to 0 is necessary. When Seq1 and Seq2 are both set to 0 or to 1, the AD7328 is configured to operate in traditional multichannel mode, where a write to Channel Address Bit ADD2 to Bit ADD0 in the control register selects the next channel for conversion.
STOPPING A SEQUENCE. CS DIN: WRITE TO CONTROL REGISTER TO STOP THE SEQUENCE, Seq1 = 0, Seq2 = 0. DOUT: CONVERSION RESULT FROM CHANNEL IN SEQUENCE.
CONTINUOUSLY CONVERT ON CONSECUTIVE SEQUENCE OF CHANNELS.
Figure 45. Flowchart for Consecutive Sequence of Channels
Rev. A | Page 26 of 36
04852-032
AD7328
REFERENCE
The AD7328 can operate with either the internal 2.5 V on-chip reference or an externally applied reference. The internal reference is selected by setting the Ref bit in the control register to 1. On power-up, the Ref bit is 0, which selects the external reference for the AD7328 conversion. Suitable reference sources for the AD7328 include AD780, AD1582, ADR431, REF193, and ADR391. The internal reference circuitry consists of a 2.5 V band gap reference and a reference buffer. When operating the AD7328 in internal reference mode, the 2.5 V internal reference is available at the REFIN/OUT pin, which should be decoupled to AGND using a 680 nF capacitor. It is recommended that the internal reference be buffered before applying it elsewhere in the system. The internal reference is capable of sourcing up to 90 A. On power-up, if the internal reference operation is required for the ADC conversion, a write to the control register is necessary to set the Ref bit to 1. During the control register write, the conversion result from the first initial conversion is invalid. The reference buffer requires 500 s to power up and charge the 680 nF decoupling capacitor during the power-up time. The AD7328 is specified for a 2.5 V to 3 V reference range. When a 3 V reference is selected, the ranges are 12 V, 6 V, 3 V, and 0 V to +12 V. For these ranges, the VDD and VSS supply must be equal to or greater than the maximum analog input range selected. ADD1, and ADD0 to 1. VIN7 must be tied to AGND or to a small dc voltage within the specified pseudo input range for the selected analog input range. When a conversion is initiated in this configuration, the output code represents the temperature (see Figure 46 and Figure 47). When using the temperature indicator on the AD7328, the part should be operated at low throughput rates, such as approximately 50 kSPS for the 10 V range and 30 kSPS for the 2.5 V range. The throughput rate is reduced for the temperature indicator mode because the AD7328 requires more acquisition time for this mode.
4420 4410 4400
ADC OUTPUT CODE
VCC = VDRIVE = 5V VDD/VSS = 12V 50kSPS
10V RANGE, INT REF 4390 4380 4370 4360
04852-033
4350 4340 -40
-20
0
20
40
60
80
100
TEMPERATURE (C)
Figure 46. Temperature vs. ADC Output Code for 10 V Range
5450 5400 5350 5300 5250 5200 5150 5100 -40 VCC = VDRIVE = 5V VDD/VSS = 12V 2.5V RANGE INT REFERENCE 30kSPS
VDRIVE
The AD7328 has a VDRIVE feature to control the voltage at which the serial interface operates. VDRIVE allows the ADC to easily interface to both 3 V and 5 V processors. For example, if the AD7328 is operated with a VCC of 5 V, the VDRIVE pin can be powered from a 3 V supply. This allows the AD7328 to accept large bipolar input signals with low voltage digital processing.
ADC OUTPUT CODE
The AD7328 has an on-chip temperature indicator. The temperature indicator can be used to provide local temperature measurements on the AD7328. To access the temperature indicator, the ADC should be configured in pseudo differential mode, Mode 1 = Mode 0 = 1, which sets Channel Bits ADD2,
-20
0
20
40
60
80
TEMPERATURE (C)
Figure 47. Temperature vs. ADC Output Code for 2.5 V Range
Rev. A | Page 27 of 36
04852-034
TEMPERATURE INDICATOR
AD7328 MODES OF OPERATION
The AD7328 has several modes of operation that are designed to provide flexible power management options. These options can be chosen to optimize the power dissipation/throughput rate ratio for different application requirements. The mode of operation of the AD7328 is controlled by the power management bits, Bit PM1 and Bit PM0, in the control register as shown in Table 11. The default mode is normal mode, where all internal circuitry is fully powered up. The AD7328 remains fully powered up at the end of the conversion if both PM1 and PM0 contain 0 in the control register. To complete the conversion and access the conversion result 16 serial clock cycles are required. At the end of the conversion, CS can idle either high or low until the next conversion. Once the data transfer is complete, another conversion can be initiated after the quiet time, tQUIET, has elapsed.
NORMAL MODE
(PM1 = PM0 = 0) This mode is intended for the fastest throughput rate performance with the AD7328 being fully powered up at all times. Figure 48 shows the general operation of the AD7328 in normal mode. The conversion is initiated on the falling edge of CS, and the trackand-hold enters hold mode, as described in the Serial Interface section. The data on the DIN line during the 16 SCLK transfer is loaded into one of the on-chip registers if the write bit is set. The register is selected by programming the register select bits (see Table 8).
CS 1 SCLK 16
FULL SHUTDOWN MODE
(PM1 = PM0 = 1) In this mode, all internal circuitry on the AD7328 is powered down. The part retains information in the registers during full shutdown. The AD7328 remains in full shutdown mode until the power management bits, Bit PM1 and Bit PM0, in the control register are changed. A write to the control register with PM1 = PM0 = 1 places the part into full shutdown mode. The AD7328 enters full shutdown mode on the 15th SCLK rising edge once the control register is updated. If a write to the control register occurs while the part is in full shutdown mode with the power management bits, Bit PM1 and Bit PM0, set to 0 (normal mode), the part begins to power up on the 15th SCLK rising edge once the control register is updated. Figure 49 shows how the AD7328 is configured to exit full shutdown mode. To ensure the AD7328 is fully powered up, tPOWER-UP should elapse before the next CS falling edge.
DOUT
3 CHANNEL I.D. BITS, SIGN BIT + CONVERSION RESULT DATA INTO CONTROL/SEQUENCE/RANGE1/RANGE2 REGISTER
04852-035
DIN
Figure 48. Normal Mode
PART IS IN FULL SHUTDOWN
THE PART IS FULLY POWERED UP ONCE tPOWER-UP HAS ELAPSED PART BEGINS TO POWER UP ON THE 15TH SCLK RISING EDGE AS PM1 = PM0 = 0
tPOWER-UP
CS 1 SCLK 16 1 16
SDATA
INVALID DATA
CHANNEL IDENTIFIER BITS + CONVERSION RESULT
DIN
DATA INTO CONTROL REGISTER CONTROL REGISTER IS LOADED ON THE FIRST 15 CLOCKS, PM1 = 0, PM0 = 0
DATA INTO CONTROL REGISTER TO KEEP THE PART IN NORMAL MODE, LOAD PM1 = PM0 = 0 IN CONTROL REGISTER
04852-041
Figure 49. Exiting Full Shutdown Mode
Rev. A | Page 28 of 36
AD7328
AUTOSHUTDOWN MODE
(PM1 = 1, PM0 = 0) Once the autoshutdown mode is selected, the AD7328 automatically enters shutdown on the 15th SCLK rising edge. In autoshutdown mode, all internal circuitry is powered down. The AD7328 retains information in the registers during autoshutdown. The track-and-hold is in hold mode during autoshutdown. On the rising CS edge, the track-and-hold, which was in hold during shutdown, returns to track as the AD7328 begins to power up. The time to power-up from auto shutdown is 500 s. When the control register is programmed to transition to autoshutdown mode, it does so on the 15th SCLK rising edge. Figure 50 shows the part entering the autoshutdown mode. Once in autoshutdown mode, the CS signal must remain low to keep the part in autoshutdown mode. The AD7328 automatically begins to power up on the CS rising edge. The tPOWER-UP is required before a valid conversion, initiated by bringing the CS signal low, can take place. Once this valid conversion is complete, the AD7328 powers down again on the 15th SCLK rising edge. The CS signal must remain low again to keep the part in autoshutdown mode.
AUTOSTANDBY MODE
(PM1 = 0, PM0 =1) In autostandby mode, portions of the AD7328 are powered down, but the on-chip reference remains powered up. The reference bit in the control register should be 1 to ensure that the on-chip reference is enabled. This mode is similar to autoshutdown but allows the AD7328 to power up much faster, which allows faster throughput rates. As is the case with autoshutdown mode, the AD7328 enters standby on the 15th SCLK rising edge once the control register is updated (see Figure 50). The part retains information in the registers during standby. The AD7328 remains in standby until it receives a CS rising edge. The ADC begins to power up on the CS rising edge. On the CS rising edge, the track-and-hold, which was in hold mode while the part was in standby, returns to track. The power-up time from standby is 700 ns. The user should ensure that 700 ns have elapsed before bringing CS low to attempt a valid conversion. Once this valid conversion is complete, the AD7328 again returns to standby on the 15th SCLK rising edge. The CS signal must remain low to keep the part in standby mode. Figure 50 shows the part entering autoshutdown mode. The sequence of events is the same when entering autostandby mode. In Figure 50, the power management bits are configured for autoshutdown. For autostandby mode, the power management bits, PM1 and PM0, should be set to 0 and 1, respectively.
PART BEGINS TO POWER UP ON CS RISING EDGE PART ENTERS SHUTDOWN MODE ON THE 15TH RISING SCLK EDGE AS PM1 = 1, PM0 = 0
THE PART IS FULLY POWERED UP ONCE tPOWER-UP HAS ELAPSED
tPOWER-UP
CS 1 SCLK
15 16
1
15 16
SDATA
VALID DATA
VALID DATA
DIN
DATA INTO CONTROL REGISTER CONTROL REGISTER IS LOADED ON THE FIRST 15 CLOCKS, PM1 = 1, PM0 = 0
DATA INTO CONTROL REGISTER
04852-042
Figure 50. Entering Autoshutdown/Autostandby Mode
Rev. A | Page 29 of 36
AD7328
POWER VS. THROUGHPUT RATE
The power consumption of the AD7328 varies with throughput rate. The static power consumed by the AD7328 is very low, and significant power savings can be achieved as the throughput rate is reduced. Figure 51 and Figure 52 shows the power vs. throughput rate for the AD7328 at a VCC of 3 V and 5 V, respecttively. Both plots clearly show that the average power consumed by the AD7328 is greatly reduced as the sample frequency is reduced. This is true whether a fixed SCLK value is used or if it is scaled with the sampling frequency. Figure 51 and Figure 52 show the power consumption when operating in normal mode for a fixed 20 MHz SCLK and a variable SCLK that scales with the sampling frequency.
12 20 18 16
AVERAGE POWER (mW)
VARIABLE SCLK 20MHz SCLK
14 12 10 8 6 4 2 0 0 100 200 300 400 500
600
700
800
900
1000
THROUGHPUT RATE (kHz)
Figure 52. Power vs. Throughput Rate with 5 V VCC
10
AVERAGE POWER (mW)
8
20MHz SCLK VARIABLE SCLK
6
4 VCC = 3V VDD/VSS = 12V TA = 25C INTERNAL REFERENCE 0 100 200 300 400 500 600 700 800
2
0
900 1000 1100
THROUGHPUT RATE (kSPS)
Figure 51. Power vs. Throughput Rate with 3 V VCC
04852-052
Rev. A | Page 30 of 36
04852-053
VCC = 5V VDD/VSS = 12V TA = 25C INTERNAL REFERENCE
AD7328 SERIAL INTERFACE
Figure 53 shows the timing diagram for the serial interface of the AD7328. The serial clock applied to the SCLK pin provides the conversion clock and controls the transfer of information to and from the AD7328 during a conversion. The CS signal initiates the data transfer and the conversion process. The falling edge of CS puts the track-and-hold into hold mode and takes the bus out of three-state. The analog input signal is then sampled. Once the conversion is initiated, it requires 16 SCLK cycles to complete. The track-and-hold goes back into track mode on the 14th SCLK rising edge. On the 16th SCLK falling edge, the DOUT line returns to three-state. If the rising edge of CS occurs before 16 SCLK cycles have elapsed, the conversion is terminated and the DOUT line returns to three-state. Depending on where the CS signal is brought high, the addressed register may be updated. Data is clocked into the AD7328 on the SCLK falling edge. The three MSBs on the DIN line are decoded to select which register is addressed. The control register is a 12-bit register. If the control register is addressed by the three MSBs, the data on the DIN line is loaded into the control on the 15th SCLK rising edge. If the sequence register or either of the range registers is addressed, the data on the DIN line is loaded into the addressed register on the 11th SCLK falling edge. Conversion data is clocked out of the AD7328 on each SCLK falling edge. Data on the DOUT line consists of three channel identifier bits, a sign bit, and a 12-bit conversion result. The channel identifier bits are used to indicate which channel corresponds to the conversion result. If the Weak/Three-State bit is set in the control register, rather than returning to true three-state upon the 16th SCLK falling edge, the DOUT line is pulled weakly to the logic level corresponding to ADD3 of the next serial transfer. This is done to ensure that the MSB of the next serial transfer is set up in time for the first SCLK falling edge after the CS falling edge. If the Weak/Three-State bit is set to 0 and the DOUT line returns to true three-state between conversions, then depending on the particular processor interfacing to the AD7328, the ADD3 bit may be valid in time for the processor to clock it in successfully. If the Weak/Three-State bit is set to 1, then although the DOUT line has been driven to ADD3 since the previous conversion, it is nevertheless so weakly driven that another device could take control of the bus. This will not lead to a bus contention issue because, for example, a 10 k pull-up or pull-down resistor is sufficient to overdrive the logic level of ADD3. When the Weak/ Three-State bit is set to 1, the ADD3 is typically valid 9 ns after the CS falling edge, compared with 14 ns when the DOUT line returns to three-state at the end of the conversion.
t1
CS
t2
SCLK 1 2 3 4 3 IDENTIFICATION BITS
tCONVERT t6
5 13 14 15 16
t3
t4
DB11
t7
DB10 DB2
t5
DB1 DB0
t8
DOUT THREE- ADD2 STATE DIN
ADD1
ADD0
SIGN
tQUIET
t9
REG SEL1 REG SEL2 MSB
t10
LSB DON'T CARE
THREE-STATE
04852-036
WRITE
Figure 53. Serial Interface Timing Diagram (Control Register Write)
Rev. A | Page 31 of 36
AD7328 MICROPROCESSOR INTERFACING
The serial interface on the AD7328 allows the part to be directly connected to a range of different microprocessors. This section explains how to interface the AD7328 with some common microcontroller and DSP serial interface protocols. The frequency of the serial clock is set in the SCLKDIV register. When the instruction to transmit with TFS is given (AX0 = TX0), the state of the serial clock is checked. The DSP waits until the SCLK has gone high, low, and high again before starting the transmission. If the timer and SCLK are chosen so that the instruction to transmit occurs on or near the rising edge of SCLK, data can be transmitted immediately or at the next clock edge. For example, the ADSP-2111 has a master clock frequency of 16 MHz. If the SCLKDIV register is loaded with the value 3, an SCLK of 2 MHz is obtained, and eight master clock periods elapse for every one SCLK period. If the timer registers are loaded with the value 803, 100.5 SCLKs occur between interrupts and, subsequently, between transmit instructions. This situation leads to nonequidistant sampling because the transmit instruction occurs on an SCLK edge. If the number of SCLKs between interrupts is an integer of N, equidistant sampling is implemented by the DSP.
AD7328 TO ADSP-21xx
The ADSP-21xx family of DSPs interface directly to the AD7328 without requiring glue logic. The VDRIVE pin of the AD7328 takes the same supply voltage as that of the ADSP-21xx. This allows the ADC to operate at a higher supply voltage than its serial interface. The SPORT0 on the ADSP-21xx should be configured as shown in Table 14. Table 14. SPORT0 Control Register Setup
Setting TFSW = RFSW = 1 INVRFS = INVTFS = 1 DTYPE = 00 SLEN = 1111 ISCLK = 1 TFSR = RFSR = 1 IRFS = 0 ITFS = 1 Description Alternative framing Active low frame signal Right justify data 16-bit data-word Internal serial clock Frame every word
AD7328 TO ADSP-BF53x
The ADSP-BF53x family of DSPs interfaces directly to the AD7328 without requiring glue logic, as shown in Figure 55. The SPORT0 Receive Configuration 1 register should be set up as outlined in Table 15.
AD73281
SCLK CS DIN DOUT VDRIVE
The connection diagram is shown in Figure 54. The ADSP-21xx has TFS0 and RFS0 tied together. TFS0 is set as an output, and RFS0 is set as an input. The DSP operates in alternative framing mode, and the SPORT0 control register is set up as described in Table 14. The frame synchronization signal generated on TFS is tied to CS and, as with all signal processing applications, requires equidistant sampling. However, as in this example, the timer interrupt is used to control the sampling rate of the ADC, and under certain conditions equidistant sampling cannot be achieved.
AD73281
SCLK CS
ADSP-BF53x1
RSCLK0 RFS0 DT0 DR0
VDD
1ADDITIONAL
SCLK0 TFS0 RFS0 DT0 DR0
PINS OMITTED FOR CLARITY.
Figure 55. Interfacing the AD7328 to the ADSP-BF53x
Table 15. SPORT0 Receive Configuration 1 Register
Setting RCKFE = 1 LRFS = 1 RFSR = 1 IRFS = 1 RLSBIT = 0 RDTYPE = 00 IRCLK = 1 RSPEN = 1 SLEN = 1111 TFSR = RFSR = 1 Description Sample data with falling edge of RSCLK Active low frame signal Frame every word Internal RFS used Receive MSB first Zero fill Internal receive clock Receive enable 16-bit data-word
DIN DOUT VDRIVE
VDD
1ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 54. Interfacing the AD7328 to the ADSP-21xx
The timer registers are loaded with a value that provides an interrupt at the required sampling interval. When an interrupt is received, a value is transmitted with TFS/DT (ADC control word). The TFS is used to control the RFS and, hence, the reading of data.
04852-037
Rev. A | Page 32 of 36
04852-038
ADSP-21xx1
AD7328 APPLICATION HINTS
LAYOUT AND GROUNDING
The printed circuit board that houses the AD7328 should be designed so that the analog and digital sections are confined to certain areas of the board. This design facilitates the use of ground planes that can be easily separated. To provide optimum shielding for ground planes, a minimum etch technique is generally best. All AGND pins on the AD7328 should be connected to the AGND plane. Digital and analog ground pins should be joined in only one place. If the AD7328 is in a system where multiple devices require an AGND and DGND connection, the connection should still be made at only one point. A star point should be established as close as possible to the ground pins on the AD7328. Good connections should be made to the power and ground planes. This can be done with a single via or multiple vias for each supply and ground pin. Avoid running digital lines under the AD7328 device because this couples noise onto the die. However, the analog ground plane should be allowed to run under the AD7328 to avoid noise coupling. The power supply lines to the AD7328 device should use as large a trace as possible to provide low impedance paths and reduce the effects of glitches on the power supply line. To avoid radiating noise to other sections of the board, components, such as clocks, with fast switching signals should be shielded with digital ground and never run near the analog inputs. Avoid crossover of digital and analog signals. To reduce the effects of feedthrough within the board, traces should be run at right angles to each other. A microstrip technique is the best method, but its use may not be possible with a double-sided board. In this technique, the component side of the board is dedicated to ground planes, and signals are placed on the other side. Good decoupling is also important. All analog supplies should be decoupled with 10 F tantalum capacitors in parallel with 0.1 F capacitors to AGND. To achieve the best results from these decoupling components, they must be placed as close as possible to the device, ideally right up against the device. The 0.1 F capacitors should have a low effective series resistance (ESR) and low effective series inductance (ESI), such as is typical of common ceramic and surface mount types of capacitors. These low ESR, low ESI capacitors provide a low impedance path to ground at high frequencies to handle transient currents due to internal logic switching.
Rev. A | Page 33 of 36
AD7328 OUTLINE DIMENSIONS
6.60 6.50 6.40
20
11
4.50 4.40 4.30 6.40 BSC
1 10
PIN 1 0.65 BSC 0.15 0.05 COPLANARITY 0.10 0.30 0.19 1.20 MAX 0.20 0.09 8 0 0.75 0.60 0.45
SEATING PLANE
COMPLIANT TO JEDEC STANDARDS MO-153-AC
Figure 56. 20-Lead Thin Shrink Small Outline Package [TSSOP] (RU-20) Dimensions shown in millimeters
ORDERING GUIDE
Model AD7328BRUZ 1 AD7328BRUZ-REEL1 AD7328BRUZ-REEL71 EVAL-AD7328CB 2 EVAL-CONTROL BRD2 3
1 2
Temperature Range -40C to +85C -40C to +85C -40C to +85C
Package Description 20-Lead TSSOP 20-Lead TSSOP 20-Lead TSSOP Evaluation Board Controller Board
Package Option RU-20 RU-20 RU-20
Z = Pb-free part. This can be used as a stand-alone evaluation board or in conjunction with the EVAL-CONTROL board for evaluation/demonstration purposes. 3 This board is a complete unit allowing a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators. To order a complete evaluation kit, the particular ADC evaluation board (for example, EVAL-AD7328CB), the EVAL-CONTROL BRD2, and a 12 V transformer must be ordered. See the relevant evaluation board technical note for more information.
Rev. A | Page 34 of 36
AD7328 NOTES
Rev. A | Page 35 of 36
AD7328 NOTES
(c)2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04852-0-6/06(A)
Rev. A | Page 36 of 36

▲Up To Search▲

Price & Availability of AD7328BRUZ

	To Download AD7328BRUZ Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .