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LTC1863/LTC1867 12-/16-Bit, 8-Channel 200ksps ADCs
FEATURES
s s s
DESCRIPTIO
s s s s s s s s
Sample Rate: 200ksps 16-Bit No Missing Codes and 2LSB Max INL 8-Channel Multiplexer with: Single Ended or Differential Inputs and Unipolar or Bipolar Conversion Modes SPI/MICROWIRETM Serial I/O Signal-to-Noise Ratio: 89dB Single 5V Operation On-Chip or External Reference Low Power: 1.3mA at 200ksps, 0.76mA at 100ksps Sleep Mode Automatic Nap Mode Between Conversions 16-Pin Narrow SSOP Package
The LTC(R)1863/LTC1867 are pin-compatible, 8-channel 12-/16-bit A/D converters with serial I/O, and an internal reference. The ADCs typically draw only 1.3mA from a single 5V supply. The 8-channel input multiplexer can be configured for either single-ended or differential inputs and unipolar or bipolar conversions (or combinations thereof). The automatic nap and sleep modes benefit power sensitive applications. The LTC1867's DC performance is outstanding with a 2LSB INL specification and no missing codes over temperature. The signal-to-noise ratio (SNR) for the LTC1867 is typically 89dB, with the internal reference. Housed in a compact, narrow 16-pin SSOP package, the LTC1863/LTC1867 can be used in space-sensitive as well as low-power applications.
, LTC and LT are registered trademarks of Linear Technology Corporation. MICROWIRE is a trademark of National Semiconductor Corp.
APPLICATIO S
s s s s s
Industrial Process Control High Speed Data Acquisition Battery Operated Systems Multiplexed Data Acquisition Systems Imaging Systems
BLOCK DIAGRA
1 2 3 4 5 6 7 8
Integral Nonlinearity vs Output Code (LTC1867)
2.0
CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7/COM LTC1863/LTC1867 16 V DD 15 GND 14 SDI 13 + 12-/16-BIT SERIAL SDO 200ksps 12 PORT - SCK ADC 11 CS/CONV 10 VREF INTERNAL 2.5V REF 9
18637 BD
1.5 1.0
INL (LBS)
ANALOG INPUT MUX
0.5 0 - 0.5 - 1.0
REFCOMP
- 1.5 - 2.0 0 16384 32768 49152 OUTPUT CODE 65536
18637 GO1
U
18637f
W
U
1
LTC1863/LTC1867
ABSOLUTE
(Notes 1, 2)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW CH0 1 CH1 2 CH2 3 CH3 4 CH4 5 CH5 6 CH6 7 CH7/COM 8 16 VDD 15 GND 14 SDI 13 SDO 12 SCK 11 CS/CONV 10 VREF 9 REFCOMP
Supply Voltage (VDD) ................................... -0.3V to 6V Analog Input Voltage CH0-CH7/COM (Note 3) .......... - 0.3V to (VDD + 0.3V) VREF, REFCOMP (Note 4)......... - 0.3V to (VDD + 0.3V) Digital Input Voltage (SDI, SCK, CS/CONV) (Note 4) .................................................- 0.3V to 10V Digital Output Voltage (SDO) ....... - 0.3V to (VDD + 0.3V) Power Dissipation .............................................. 500mW Operating Temperature Range LTC1863C/LTC1867C/LTC1867AC .......... 0C to 70C LTC1863I/LTC1867I/LTC1867AI ........ - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1863CGN LTC1863IGN LTC1867CGN LTC1867IGN LTC1867ACGN LTC1867AIGN GN PART MARKING 1863 1867
GN PACKAGE 16-LEAD NARROW PLASTIC SSOP TJMAX = 110C, JA = 95C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
CO VERTER CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25C. With external reference (Notes 5, 6)
PARAMETER Resolution No Missing Codes Integral Linearity Error Differential Linearity Error Transition Noise Offset Error Offset Error Match Offset Error Drift Gain Error Gain Error Match Gain Error Tempco Power Supply Sensitivity Internal Reference External Reference VDD = 4.75V - 5.25V 15 2.7 1 Unipolar Bipolar Unipolar (Note 8) Bipolar Unipolar Bipolar 0.5 6 6 1 15 2.7 5
q q
CONDITIONS
q q
MIN 12 12
LTC1863 TYP MAX
MIN 16 15
LTC1867 TYP MAX
MIN 16 16
LTC1867A TYP MAX
UNITS Bits Bits
Unipolar (Note 7) Bipolar
q q q
1 1 1 0.1 3 4 1 1 0.5 -2 0.74
4 4 3 32 64 2 2 0.5 96 96 4 15 2.7 5 -1 0.74
2 2.5 1.75 32 64 2 2 64 64 2
LSBRMS LSB LSB LSB LSB ppm/C LSB LSB LSB ppm/C ppm/C LSB
DY A IC ACCURACY
SYMBOL SNR S/(N+D) PARAMETER Signal-to-Noise Ratio Signal-to-(Noise + Distortion) Ratio
(Note 5)
CONDITIONS 1kHz Input Signal 1kHz Input Signal MIN LTC1863 TYP MAX 73.6 73.5 LTC1867/LTC1867A MIN TYP MAX 89 88 UNITS dB dB
18637f
2
U
LSB LSB LSB
W
U
U
WW
W
WU
U
LTC1863/LTC1867
DY A IC ACCURACY
SYMBOL THD PARAMETER Total Harmonic Distortion Peak Harmonic or Spurious Noise Channel-to-Channel Isolation Full Power Bandwidth
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
SYMBOL PARAMETER Analog Input Range CIN tACQ Analog Input Capacitance for CH0 to CH7/COM Sample-and-Hold Acquisition Time Input Leakage Current On Channels, CHX = 0V or VDD CONDITIONS Unipolar Mode (Note 9) Bipolar Mode Between Conversions (Sample Mode) During Conversions (Hold Mode)
q q q q
A ALOG I PUT
I TER AL REFERE CE CHARACTERISTICS
PARAMETER VREF Output Voltage VREF Output Tempco VREF Line Regulation VREF Output Resistance REFCOMP Output Voltage CONDITIONS IOUT = 0 IOUT = 0 4.75V VDD 5.25V IOUT 0.1mA IOUT = 0
DIGITAL I PUTS A D DIGITAL OUTPUTS
SYMBOL VIH VIL IIN CIN VOH VOL ISOURCE ISINK PARAMETER High Level Input Voltage Low Level Input Voltage Digital Input Current Digital Input Capacitance High Level Output Voltage (SDO) Low Level Output Voltage (SDO) Output Source Current Output Sink Current Hi-Z Output Leakage Hi-Z Output Capacitance Data Format CONDITIONS VDD = 5.25V VDD = 4.75V VIN = 0V to VDD
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
LTC1863/LTC1867/LTC1867A MIN TYP MAX
q q q
U
U
U
U
WU
U
(Note 5)
CONDITIONS 1kHz Input Signal, Up to 5th Harmonic 1kHz Input Signal 100kHz Input Signal -3dB Point MIN LTC1863 TYP MAX -94.5 -94.5 -100 1.25 LTC1867/LTC1867A MIN TYP MAX - 95 - 95 -117 1.25 UNITS dB dB dB MHz
U
LTC1863/LTC1867/LTC1867A MIN TYP MAX 0-4.096 2.048 32 4 1.5 1.1 1
UNITS V V pF pF s A
U
(Note 5)
LTC1863/LTC1867/LTC1867A MIN TYP MAX 2.480 2.500 15 0.43 6 4.096 2.520 UNITS V ppm/C mV/V k V
UNITS V V A pF V V
2.4 0.8 10 2 4.75 4.74 0.05 0.10 -32 19 0.4
VDD = 4.75V, IO = -10A VDD = 4.75V, IO = -200A VDD = 4.75V, IO = 160A VDD = 4.75V, IO = 1.6mA SDO = 0V SDO = VDD CS/CONV = High, SDO = 0V or VDD CS/CONV = High (Note 10) Unipolar Bipolar
q q
4
V V mA mA
q q
10 15 Straight Binary Two's Complement
A pF
18637f
3
LTC1863/LTC1867
POWER REQUIRE E TS
SYMBOL VDD IDD PARAMETER Supply Voltage Supply Current
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
CONDITIONS (Note 9) fSAMPLE = 200ksps NAP Mode SLEEP Mode
q q q
PDISS
Power Dissipation
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
SYMBOL fSAMPLE tCONV tACQ fSCK t1 t2 t3 t4 t5 t6 t7 t8 PARAMETER Maximum Sampling Frequency Conversion Time Acquisition Time SCK Frequency CS/CONV High Time SDO Valid After SCK SDO Valid Hold Time After SCK SDO Valid After CS/CONV SDI Setup Time Before SCK SDI Hold Time After SCK SLEEP Mode Wake-Up Time Bus Relinquish Time After CS/CONV CREFCOMP = 10F, CVREF = 2.2F CL = 25pF
q
TI I G CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to GND (unless otherwise noted). Note 3: When these pin voltages are taken below GND or above VDD, they will be clamped by internal diodes. This product can handle input currents of greater than 100mA without latchup. Note 4: When these pin voltages are taken below GND, they will be clamped by internal diodes. This product can handle input currents of greater than 100mA below GND without latchup. These pins are not clamped to VDD. Note 5: VDD = 5V, fSAMPLE = 200ksps at 25C, t r = t f = 5ns and VIN - = 2.5V for bipolar mode unless otherwise specified.
4
UW
LTC1863/LTC1867/LTC1867A MIN TYP MAX 4.75 1.3 150 0.2 6.5 5.25 1.8 3 9
UNITS V mA A A mW
UW
CONDITIONS
q q q
LTC1863/LTC1867/LTC1867A MIN TYP MAX 200 3 1.5 40 5 15 10 1.1 40 100 13 11 10 -6 4 60 20 40 30 22 3.5
UNITS kHz s s MHz ns ns ns ns ns ns ms ns
Short CS/CONV Pulse Mode CL = 25pF (Note 11) CL = 25pF CL = 25pF
q q q q q q
Note 6: Linearity, offset and gain error specifications apply for both unipolar and bipolar modes. The INL and DNL are tested in bipolar mode. Note 7: Integral nonlinearity is defined as the deviation of a code from a straight line passing through the actual endpoints of the transfer curve. The deviation is measured from the center of the quantization band. Note 8: Unipolar offset is the offset voltage measured from +1/2LSB when the output code flickers between 0000 0000 0000 0000 and 0000 0000 0000 0001 for LTC1867 and between 0000 0000 0000 and 0000 0000 0001 for LTC1863. Bipolar offset is the offset voltage measured from -1/2LSB when output code flickers between 0000 0000 0000 0000 and 1111 1111 1111 1111 for LTC1867, and between 0000 0000 0000 and 1111 1111 1111 for LTC1863. Note 9: Recommended operating conditions. The input range of 2.048V for bipolar mode is measured with respect to VIN - = 2.5V. Note 10: Guaranteed by design, not subject to test. Note 11: t2 of 25ns maximum allows fSCK up to 20MHz for rising capture with 50% duty cycle and fSCK up to 40MHz for falling capture (with 3ns setup time for the receiving logic).
18637f
LTC1863/LTC1867 TYPICAL PERFOR A CE CHARACTERISTICS
Integral Nonlinearity vs Output Code
2.0 1.5 1.0 DNL (LSB) INL (LSB) 0.5 0 - 0.5 - 1.0 - 1.5 - 2.0 0 16384 32768 49152 OUTPUT CODE 65536
18637 GO1
0 - 0.5 - 1.0
COUNTS
4096 Points FFT Plot (fIN = 1kHz)
0 -20 -40 AMPLITUDE (dB) -60 -80 -100 -120 -140 0 25 50 FREQUENCY (kHz)
18637 G04
-40 AMPLITUDE (dB) -60 -80 -100 -120 -140
RESULTING AMPLITUDE ON SELECTED CHANNEL (dB)
SNR = 88.8dB SINAD = 87.9dB THD = 95dB fSAMPLE = 200ksps INTERNAL REFERENCE
75
Signal-to-Noise Ratio vs Frequency
100 90 80 AMPLITUDE (dB) AMPLITUDE (dB) 70 60 50 40 30 20 1 10 INPUT FREQUENCY (kHz) 100
18637 G07
70 60 50 40 30 20 1 10 INPUT FREQUENCY (kHz) 100
18637 G08
AMPLITUDE (dB)
UW
(LTC1867)
Differential Nonlinearity vs Output Code
2.0 1.5 1.0 0.5 2000 2500
Histogram for 4096 Conversions
2152
1500
1000
935 579
500 - 1.5 - 2.0 0 16384 32768 49152 OUTPUT CODE 65536
18637 GO2
276 0 1 26 -2 -1 0 CODE
18637 GO3
122 1 2
5 3
0 4
-4 -3
4096 Points FFT Plot (fIN = 1kHz, REFCOMP = External 5V)
0 -20 SNR = 90dB SINAD = 88.5dB THD = 94dB fSAMPLE = 200ksps VREF = 0V REFCOMP = EXT 5V -80 -90 -100 -110 -120
Crosstalk vs Input Frequency
ADJACENT PAIR
NONADJACENT PAIR -130 -140
100
0
25
50 FREQUENCY (kHz)
75
100
18637 G05
1
10 100 1000 ACTIVE CHANNEL INPUT FREQUENCY (kHz)
18637 G06
Signal-to-(Noise + Distortion) vs Input Frequency
100 90 80 -20 -30 -40 -50 -60 -70 -80 -90 -100
Total Harmonic Distortion vs Input Frequency
1
10 INPUT FREQUENCY (kHz)
100
18637 G09
18637f
5
LTC1863/LTC1867 TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs fSAMPLE
2.0 VDD = 5V 1.5 VDD = 5V fSAMPLE = 200ksps 1.4 SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
1.5
1.0
0.5
0
1
10 100 fSAMPLE (ksps)
Integral Nonlinearity vs Output Code (LTC1863)
1.0 0.8 0.6 0.4 DNL (LBS) INL (LBS) 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 512 1024 1536 2048 2560 3072 3584 4096 OUTPUT CODE
18637 G13
6
UW
18637 G10
(LTC1863/LTC1867)
Supply Current vs Supply Voltage
1.5
Supply Current vs Temperature
VDD = 5V fSAMPLE = 200ksps
1.4
1.3
1.3
1.2
1.2
1.1
1.1
1000
1.0 4.5
5.0 4.75 5.25 SUPPLY VOLTAGE (V)
5.5
18637 G11
1.0 -50
-25
0 25 50 TEMPERATURE (C)
75
100
18637 G12
Differential Nonlinearity vs Output Code (LTC1863)
1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 512 1024 1536 2048 2560 3072 3584 4096 OUTPUT CODE
18637 G14
18637f
LTC1863/LTC1867
PI FU CTIO S
CHO-CH7/COM (Pins 1-8): Analog Input Pins. Analog inputs must be free of noise with respect to GND. CH7/ COM can be either a separate channel or the common minus input for the other channels. REFCOMP (Pin 9): Reference Buffer Output Pin. Bypass to GND with 10F tantalum capacitor in parallel with 0.1F ceramic capacitor (4.096V Nominal). To overdrive REFCOMP, tie VREF to GND. VREF (Pin 10): 2.5V Reference Output. This pin can also be used as an external reference buffer input for improved accuracy and drift. Bypass to GND with 2.2F tantalum capacitor in parallel with 0.1F ceramic capacitor. CS/CONV (Pin 11): This input provides the dual function of initiating conversions on the ADC and also frames the serial data transfer. SCK (Pin 12): Shift Clock. This clock synchronizes the serial data transfer. SDO (Pin 13): Digital Data Output. The A/D conversion result is shifted out of this output. Straight binary format for unipolar mode and two's complement format for bipolar mode. SDI (Pin 14): Digital Data Input Pin. The A/D configuration word is shifted into this input. GND (Pin 15): Analog and Digital GND. VDD (Pin 16): Analog and Digital Power Supply. Bypass to GND with 10F tantalum capacitor in parallel with 0.1F ceramic capacitor.
TYPICAL CO
ECTIO
DIAGRA
2.048V DIFFERENTIAL INPUTS
+ -
CH0 CH1 CH2 CH3
4.096V SINGLE-ENDED INPUT
+
CH4 CH5 CH6 CH7/COM
TEST CIRCUITS
Load Circuits for Access Timing
5V 3k DN 3k CL DN CL DN 3k CL DN CL
(A) Hi-Z TO VOH AND VOL TO VOH
(B) Hi-Z TO VOL AND VOH TO VOL
18637 TC01
U U
U
UU
U
U
U
VDD GND SDI LTC1863/ SDO LTC1867 SCK CS/CONV VREF REFCOMP
5V
DIGITAL I/O
2.5V 2.2F 4.096V 10F
18637 TCD
Load Circuits for Output Float Delay
5V 3k
(A) VOH TO Hi-Z
(B) VOL TO Hi-Z
18637 TC02
18637f
7
LTC1863/LTC1867
TI I G DIAGRA S
t1 (For Short Pulse Mode)
t1 CS/CONV 50% 50%
t4 (SDO Valid After CONV)
t4 CS/CONV SCK
0.4V
SDO
Hi-Z
t7 (SLEEP Mode Wake-Up Time)
t7 SCK 50% SLEEP BIT (SLP = 0) READ-IN CS/CONV 50% SDO CS/CONV
APPLICATIO S I FOR ATIO
Overview
The LTC1863/LTC1867 are complete, low power multiplexed ADCs. They consist of a 12-/16-bit, 200ksps capacitive successive approximation A/D converter, a precision internal reference, a configurable 8-channel analog input multiplexer (MUX) and a serial port for data transfer. Conversions are started by a rising edge on the CS/CONV input. Once a conversion cycle has begun, it cannot be restarted. Between conversions, the ADCs receive an input word for channel selection and output the conversion result, and the analog input is acquired in preparation for the next conversion. In the acquire phase, a minimum time of 1.5s will provide enough time for the sample-and-hold capacitors to acquire the analog signal.
8
U
W
W
UU
UW
t2 (SDO Valid Before SCK), t 3 (SDO Valid Hold Time After SCK)
t2 SCK 0.4V t3 2.4V 0.4V
SDO
t 5 (SDI Setup Time Before SCK), t6 (SDI Hold Time After SCK)
t5 2.4V t6
2.4V 0.4V
SDI
2.4V 0.4V
2.4V 0.4V
t 8 (BUS Relinquish Time)
t8 2.4V
90% 10%
Hi-Z
1867 TD
During the conversion, the internal differential 16-bit capacitive DAC output is sequenced by the SAR from the most significant bit (MSB) to the least significant bit (LSB). The input is sucessively compared with the binary weighted charges supplied by the differential capacitive DAC. Bit decisions are made by a low-power, differential comparator. At the end of a conversion, the DAC output balances the analog input. The SAR contents (a 12-/16-bit data word) that represent the analog input are loaded into the 12-/16-bit output latches.
18637f
LTC1863/LTC1867
APPLICATIO S I FOR ATIO
Analog Input Multiplexer
The analog input multiplexer is controlled by a 7-bit input data word. The input data word is defined as follows: SD OS S1 S0 COM UNI SLP SD = SINGLE/DIFFERENTIAL BIT OS = ODD/SIGN BIT S1 = ADDRESS SELECT BIT 1 S0 = ADDRESS SELECT BIT 0 COM = CH7/COM CONFIGURATION BIT UNI = UNIPOLAR/BIPOLAR BIT SLP = SLEEP MODE BIT
Examples of Multiplexer Options
4 Differential 8 Single-Ended
+ (-) - (+) { + (-) - (+) { + (-) - (+) { + (-) - (+) {
CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7/COM
+ + + + + + + +
CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7/COM GND (-)
7 Single-Ended to CH7/COM
Combinations of Differential and Single-Ended
+ + + + + + +
CH0 CH1 CH2 CH3 CH4 CH5 CH6
+ -{ - +{ + + + +
CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7/COM GND (-)
18637 AI01
CH7/COM (-)
U U
Changing the MUX Assignment "On the Fly"
1st Conversion 2nd Conversion
W W
UU UU
+ -{ + -{
CH2 CH3 CH4 CH5 CH7/COM (UNUSED)
- + + +
{ {
CH2 CH3 CH4 CH5 CH7/COM (-)
18637 AI02
Tables 1 and 2 show the configurations when COM = 0, and COM = 1.
Table 1. Channel Configuration (When COM = 0, CH7/COM Pin Is Used as CH7)
SD 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 OS 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 S1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 S0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 COM 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Channel Configuration "+" "-" CH0 CH2 CH4 CH6 CH1 CH3 CH5 CH7 CH0 CH2 CH4 CH6 CH1 CH3 CH5 CH7 CH1 CH3 CH5 CH7 CH0 CH2 CH4 CH6 GND GND GND GND GND GND GND GND
Table 2. Channel Configuration (When COM = 1, CH7/COM Pin Is Used as COMMON)
SD 1 1 1 1 1 1 1 OS 0 0 0 0 1 1 1 S1 0 0 1 1 0 0 1 S0 0 1 0 1 0 1 0 COM 1 1 1 1 1 1 1 Channel Configuration "+" "-" CH0 CH2 CH4 CH6 CH1 CH3 CH5 CH7/COM CH7/COM CH7/COM CH7/COM CH7/COM CH7/COM CH7/COM
18637f
9
LTC1863/LTC1867
APPLICATIO S I FOR ATIO
Driving the Analog Inputs
The analog inputs of the LTC1863/LTC1867 are easy to drive. Each of the analog inputs can be used as a singleended input relative to the GND pin (CH0-GND, CH1-GND, etc) or in pairs (CH0 and CH1, CH2 and CH3, CH4 and CH5, CH6 and CH7) for differential inputs. In addition, CH7 can act as a COM pin for both single-ended and differential modes if the COM bit in the input word is high. Regardless of the MUX configuration, the "+" and "-" inputs are sampled at the same instant. Any unwanted signal that is common mode to both inputs will be reduced by the common mode rejection of the sample-and-hold circuit. The inputs draw only one small current spike while charging the sample-and-hold capacitors during the acquire mode. In conversion mode, the analog inputs draw only a small leakage current. If the source impedance of the driving circuit is low then the LTC1863/LTC1867 inputs can be driven directly. More acquisition time should be allowed for a higher impedance source. The following list is a summary of the op amps that are suitable for driving the LTC1863/LTC1867. More detailed information is available in the Linear Technology data books or Linear Technology website. LT1007 - Low noise precision amplifier. 2.7mA supply current 5V to 15V supplies. Gain bandwidth product 8MHz. DC applications. LT1097 - Low cost, low power precision amplifier. 300A supply current. 5V to 15V supplies. Gain bandwidth product 0.7MHz. DC applications. LT1227 - 140MHz video current feedback amplifier. 10mA supply current. 5V to 15V supplies. Low noise and low distortion.
10
U
LT1360 - 37MHz voltage feedback amplifier. 3.8mA supply current. 5V to 15V supplies. Good AC/DC specs. LT1363 - 50MHz voltage feedback amplifier. 6.3mA supply current. Good AC/DC specs. LT1364/LT1365 - Dual and quad 50MHz voltage feedback amplifiers. 6.3mA supply current per amplifier. Good AC/DC specs. LT1468 - 90MHz, 22V/s 16-bit accurate amplifier LT1469 - Dual LT1468 Input Filtering The noise and the distortion of the input amplifier and other circuitry must be considered since they will add to the LTC1863/LTC1867 noise and distortion. Noisy input circuitry should be filtered prior to the analog inputs to minimize noise. A simple 1-pole RC filter is sufficient for many applications. For instance, Figure 1 shows a 50 source resistor and a 2000pF capacitor to ground on the input will limit the input bandwidth to 1.6MHz. The source impedance has to be kept low to avoid gain error and degradation in the AC performance. The capacitor also acts as a charge reservoir for the input sample-and-hold and isolates the ADC input from sampling glitch sensitive circuitry. High quality capacitors and resistors should be used since these components can add distortion. NPO and silver mica type dielectric capacitors have excellent linearity. Carbon surface mount resistors can also generate distortion from self heating and from damage that may occur during soldering. Metal film surface mount resistors are much less susceptible to both problems.
18637f
W
UU
LTC1863/LTC1867
APPLICATIO S I FOR ATIO
ANALOG INPUT 50 CH0 2000pF GND LTC1863/ LTC1867
REFCOMP 10F
1867 F01a
Figure 1a. Optional RC Input Filtering for Single-Ended Input
1000pF 50 DIFFERENTIAL ANALOG INPUTS CH0 1000pF 50 CH1 1000pF REFCOMP 10F
1867 F01b
LTC1863/ LTC1867
Figure 1b. Optional RC Input Filtering for Differential Inputs
0
DC Performance One way of measuring the transition noise associated with a high resolution ADC is to use a technique where a DC signal is applied to the input of the ADC and the resulting output codes are collected over a large number of conversions. For example, in Figure 2 the distribution of output codes is shown for a DC input that had been digitized 4096 times. The distribution is Gaussian and the RMS code transition noise is about 0.74LSB.
2500 2152 2000
AMPLITUDE (dB)
COUNTS
1500
1000
935 579
500 276 0 1 26 -2 -1 0 CODE
18637 GO3
122 1 2
5 3
0 4
-4 -3
Figure 2. LTC1867 Histogram for 4096 Conversions
U
Dynamic Performance FFT (Fast Fourier Transform) test techniques are used to test the ADC's frequency response, distortion and noise at the rated throughput. By applying a low distortion sine wave and analyzing the digital output using an FFT algorithm, the ADC's spectral content can be examined for frequencies outside the fundamental. Signal-to-Noise Ratio The Signal-to-Noise and Distortion Ratio (SINAD) is the ratio between the RMS amplitude of the fundamental input frequency to the RMS amplitude of all other frequency components at the A/D output. The output is band limited to frequencies from above DC and below half the sampling frequency. Figure 3 shows a typical SINAD of 87.9dB with a 200kHz sampling rate and a 1kHz input. When an external 5V is applied to REFCOMP (tie VREF to GND), a signal-to-noise ratio of 90dB can be achieved.
SNR = 88.8dB SINAD = 87.9dB THD = 95dB fSAMPLE = 200ksps INTERNAL REFERENCE -20 -40 -60 -80 -100 -120 -140 0 25 50 FREQUENCY (kHz)
18637 G04
W
UU
75
100
Figure 3. LTC1867 Nonaveraged 4096 Point FFT Plot
Total Harmonic Distortion Total Harmonic Distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as:
THD = 20 log V22 + V32 + V42 ... + VN2 V1
18637f
11
LTC1863/LTC1867
APPLICATIO S I FOR ATIO
where V1 is the RMS amplitude of the fundamental frequency and V2 through VN are the amplitudes of the second through Nth harmonics. Internal Reference The LTC1863/LTC1867 has an on-chip, temperature compensated, curvature corrected, bandgap reference that is factory trimmed to 2.5V. It is internally connected to a reference amplifier and is available at VREF (Pin 10). A 6k resistor is in series with the output so that it can be easily overdriven by an external reference if better drift and/or accuracy are required as shown in Figure 4. The reference amplifier gains the VREF voltage by 1.638V to 4.096V at REFCOMP (Pin 9). This reference amplifier compensation pin, REFCOMP, must be bypassed with a 10F ceramic or tantalum in parallel with a 0.1F ceramic for best noise performance.
10 VREF 2.2F 9 REFCOMP REFERENCE AMP R1 6k
2.5V
BANDGAP REFERENCE
4.096V
10F
R2 R3 LTC1863/LTC1867
1867 F04a
15 GND
Figure 4a. LT1867 Reference Circuit
5V VIN LT1019A-2.5 VOUT 10 2.2F SUPPLY CURRENT (mA) 1.5
VREF
+
10F
LTC1863/ LTC1867 9 REFCOMP
0.1F 15
GND
1867 F04b
Figure 4b. Using the LT1019-2.5 as an External Reference
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U
Digital Interface The LTC1863/LTC1867 have very simple digital interface that is enabled by the control input, CS/CONV. A logic rising edge applied to the CS/CONV input will initiate a conversion. After the conversion, taking CS/CONV low will enable the serial port and the ADC will present digital data in two's complement format in bipolar mode or straight binary format in unipolar mode, through the SCK/SDO serial port. Internal Clock The internal clock is factory trimmed to achieve a typical conversion time of 3s and a maximum conversion time, 3.5s, over the full operating temperature range. The typical acquisition time is 1.1s, and a throughput sampling rate of 200ksps is tested and guaranteed. Automatic Nap Mode The LTC1863/LTC1867 go into automatic nap mode when CS/CONV is held high after the conversion is complete. With a typical operating current of 1.3mA and automatic 150A nap mode between conversions, the power dissipation drops with reduced sample rate. The ADC only keeps the VREF and REFCOMP voltages active when the part is in the automatic nap mode. The slower the sample rate allows the power dissipation to be lower (see Figure 5).
2.0 VDD = 5V 1.0 0.5 0 1 10 100 fSAMPLE (ksps) 1000
18637 G10
W
UU
Figure 5. Supply Current vs fSAMPLE
18637f
LTC1863/LTC1867
APPLICATIO S I FOR ATIO
If the CS/CONV returns low during a bit decision, it can create a small error. For best performance ensure that the CS/CONV returns low either within 100ns after the conversion starts (i.e. before the first bit decision) or after the conversion ends. If CS/CONV is low when the conversion ends, the MSB bit will appear on SDO at the end of the conversion and the ADC will remain powered up. Sleep Mode If the SLP = 1 is selected in the input word, the ADC will enter SLEEP mode and draw only leakage current (provided that all the digital inputs stay at GND or VDD). After release from the SLEEP mode, the ADC need 60ms to wake up (2.2F/10F bypass capacitors on VREF/REFCOMP pins). Broad Layout and Bypassing To obtain the best performance, a printed circuit board with a ground plane is required. Layout for the printed circuit board should ensure digital and analog signal lines are separated as much as possible. In particular, care should be taken not to run any digital signal alongside an analog signal.
CS/CONV
tCONV
NAP MODE NOT NEEDED FOR LTC1863 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SCK
SDI Hi-Z
DON'T CARE
SD
SDO (LTC1863) SDO (LTC1867)
MSB D11 D10
Hi-Z
MSB D15 D14 D13 D12 D11 D10
Figure 6. Example 1, CS/CONV Starts a Conversion and Remains HIGH Until Next Data Transfer. With CS/CONV Remaining HIGH after the Conversion, Automatic Nap Modes Provides Power Reduction at Reduced Sample Rate.
U
All analog inputs should be screened by GND. VREF, REFCOMP and VDD should be bypassed to this ground plane as close to the pin as possible; the low impedance of the common return for these bypass capacitors is essential to the low noise operation of the ADC. The width for these tracks should be as wide as possible. Timing and Control Conversion start is controlled by the CS/CONV digital input. The rising edge transition of the CS/CONV will start a conversion. Once initiated, it cannot be restarted until the conversion is complete. Figures 6 and 7 show the timing diagrams for two types of CS/CONV pulses. Example 1 (Figure 6) shows the LTC1863/LTC1867 operating in automatic nap mode with CS/CONV signal staying HIGH after the conversion. Automatic nap mode provides power reduction at reduced sample rate. The ADCs can also operate with the CS/CONV signal returning LOW before the conversion ends. In this mode (Example 2, Figure 7), the ADCs remain powered up. Figures 8 and 9 are the transfer characteristics for the bipolar and unipolar mode.
1/fSCK 0S S1 S0 COM UNI SLP DON'T CARE D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
1867 F06
W
UU
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13
LTC1863/LTC1867
APPLICATIO S I FOR ATIO
CS/CONV
SCK
1
2
3
4
5
6
SDI
DON'T CARE t CONV
SD
0S
S1
S0
COM UNI
SDO (LTC1863) SDO (LTC1867)
MSB = D11 Hi-Z t CONV MSB = D15 Hi-Z
D10
D9
D8
D7
D6
D14 D13 D12 D11 D10
Figure 7. Example 2, CS/CONV Starts a Conversion with Short Active HIGH Pulse. With CS/CONV Returning LOW Before the Conversion, the ADC Remains Powered Up.
OUTPUT CODE (TWO'S COMPLIMENT)
011...111 011...110 BIPOLAR ZERO OUTPUT CODE
000...001 000...000 111...111 111...110 FS = 4.096 1LSB = FS/2n 1LSB = (LTC1863) = 1mV 1LSB = (LTC1867) = 62.5V -FS/2 -1 0V 1 LSB LSB INPUT VOLTAGE (V) FS/2 - 1LSB
1867 F08
100...001 100...000
Figure 8. LTC1863/LTC1867 Bipolar Transfer Characteristics (Two's Complement)
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U
tACQ NOT NEEDED FOR LTC1863 7 8 9 10 11 12 13 14 15 16 SLP DON'T CARE D5 D4 D3 D2 D1 D0 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
1867 F07
W
U
U
111...111 111...110
100...001 100...000 011...111 UNIPOLAR ZERO 011...110 FS = 4.096 1LSB = FS/2n 1LSB = (LTC1863) = 1mV 1LSB = (LTC1867) = 62.5V 0V INPUT VOLTAGE (V)
1867 F09
000...001 000...000
FS - 1LSB
Figure 9. LTC1863/LTC1867 Unipolar Transfer Characteristics (Straight Binary)
18637f
LTC1863/LTC1867
PACKAGE DESCRIPTIO U
GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.045 .005 .189 - .196* (4.801 - 4.978) 16 15 14 13 12 11 10 9 .009 (0.229) REF .150 - .165 .229 - .244 (5.817 - 6.198) .0165 .0015 .150 - .157** (3.810 - 3.988) .0250 BSC 1 .015 .004 x 45 (0.38 0.10) .007 - .0098 (0.178 - 0.249) .016 - .050 (0.406 - 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 0 - 8 TYP .0532 - .0688 (1.35 - 1.75) 23 4 56 7 8 .004 - .0098 (0.102 - 0.249) .008 - .012 (0.203 - 0.305) TYP .0250 (0.635) BSC
GN16 (SSOP) 0204
.254 MIN
RECOMMENDED SOLDER PAD LAYOUT
18637f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LTC1863/LTC1867
RELATED PARTS
PART NUMBER LTC1417 LT1460 LT1468/LT1469 LTC1609 LT1790 LTC1850/LTC1851 LTC1852/LTC1853 LTC1860/LTC1861 LTC1860L/LTC1861L LTC1864/LTC1865 LTC1864L/LTC1865L DESCRIPTION 14-Bit, 400ksps Serial ADC Micropower Precision Series Reference Single/Dual 90MHz, 22V/s, 16-Bit Accurate Op Amps 16-Bit, 200ksps Serial ADC Micropower Low Dropout Reference 10-Bit/12-Bit, 8-Channel, 1.25Msps ADC 10-Bit/12-Bit, 8-Channel, 400ksps ADC 12-Bit, 1-/2-Channel 250ksps ADC in MSOP 3V, 12-Bit, 1-/2-Channel 150ksps ADC 16-Bit, 1-/2-Channel 250ksps ADC in MSOP 3V, 16-Bit, 1-/2-Channel 150ksps ADC in MSOP COMMENTS 20mW, Unipolar or Bipolar, Internal Reference, SSOP-16 Package Bandgap, 130A Supply Current, 10ppm/C, SOT-23 Package Low Input Offset: 75V/125V 65mW, Configurable Bipolar and Unipolar Input Ranges, 5V Supply 60A Supply Current, 10ppm/C, SOT-23 Package Parallel Output, Programmable MUX and Sequencer, 5V Supply Parallel Output, Programmable MUX and Sequencer, 3V or 5V Supply 850A at 250ksps, 2A at 1ksps, SO-8 and MSOP Packages 450A at 150ksps, 10A at 1ksps, SO-8 and MSOP Packages 850A at 250ksps, 2A at 1ksps, SO-8 and MSOP Packages 450A at 150ksps, 10A at 1ksps, SO-8 and MSOP Packages
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
LT/TP 0504 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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