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FEATURES Complete Monolithic 12-Bit A/D Converters with Reference, Clock, and Three-State Output Buffers Industry Standard Pinout High Speed Upgrades for AD574A 8- and 16-Bit Microprocessor Interface 8 s (max) Conversion Time (AD774B) 15 s (max) Conversion Time (AD674B) 5 V, 10 V, 0-10 V, 0-20 V Input Ranges Commercial, Industrial and Military Temperature Range Grades MIL-STD-883 Compliant Versions Available
+5V SUPPLY V LOGIC DATA MODE SELECT 12/8 CHIP SELECT CS BYTE ADDRESS/ SHORT CYCLE A0 READ/ CONVERT R/C CHIP ENABLE CE +12/+15V SUPPLY VCC +10V REFERENCE REF OUT ANALOG COMMON AC REFERENCE INPUT REF IN _ 12/_ 15V SUPPLY V EE BIPOLAR OFFSET BIPOFF 10V SPAN INPUT 10V IN 20V SPAN INPUT 20V IN
Complete 12-Bit A/D Converters AD674B*/AD774B*
FUNCTIONAL BLOCK DIAGRAM
STATUS
1
28 STS
2
3 CONTROL
MSB
3 S T A T E N Y B B L E A O U T P U T B U F F E R S
27 26 25 24 23 22
DB11 (MSB) DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 (LSB) DIGITAL COMMON DC DIGITAL DATA OUTPUTS
4 5 6 7
I DAC CLOCK SAR COMP
12 12
8 9
10
10V REF I REF 19.95k
N Y B B L E B
21
20 19 18 17 16 15
11 12 13 14 DAC VOLTAGE DIVIDER N
12
V EE
N Y B B L E C
LSB
AD674B/AD774B
PRODUCT DESCRIPTION
PRODUCT HIGHLIGHTS
The AD674B and AD774B are complete 12-bit successiveapproximation analog-to-digital converters with three-state output buffer circuitry for direct interface to 8- and 16-bit microprocessor busses. A high precision voltage reference and clock are included on chip, and the circuit requires only power supplies and control signals for operation. The AD674B and AD774B are pin compatible with the industry standard AD574A, but offer faster conversion time and busaccess speed than the AD574A and lower power consumption. The AD674B converts in 15 s (maximum) and the AD774B converts in 8 s (maximum). The monolithic design is implemented using Analog Devices' BiMOS II process allowing high performance bipolar analog circuitry to be combined on the same die with digital CMOS logic. Offset, linearity and scaling errors are minimized by active lasertrimming of thin-film resistors. Five different grades are available. The J and K grades are specified for operation over the 0C to +70C temperature range. The A and B grades are specified from -40C to +85C, the T grade is specified from -55C to +125C. The J and K grades are available in a 28-pin plastic DIP or 28-lead SOIC. All other grades are available in a 28-pin hermetically sealed ceramic DIP.
1. Industry Standard Pinout: The AD674B and AD774B utilize the pinout established by the industry standard AD574A. 2. Analog Operation: The precision, laser-trimmed scaling and bipolar offset resistors provide four calibrated ranges: 0 to +10 V and 0 to +20 V unipolar; -5 V to +5 V and -10 V to +10 V bipolar. The AD674B and AD774B operate on +5 V and 12 V or 15 V power supplies. 3. Flexible Digital Interface: On-chip multiple-mode three-state output buffers and interface logic allow direct connection to most microprocessors. The 12 bits of output data can be read either as one 12-bit word or as two 8-bit bytes (one with 8 data bits, the other with 4 data bits and 4 trailing zeros). 4. The internal reference is trimmed to 10.00 volts with 1% maximum error and 10 ppm/C typical temperature coefficient. The reference is available externally and can drive up to 2.0 mA beyond the requirements of the converter and bipolar offset resistors. 5. The AD674B and AD774B are available in versions compliant with MIL-STD-883. Refer to the Analog Devices Military Products Databook or current AD674B/AD774B/883B data sheet for detailed specifications.
*Protected by U.S. Patent Nos. 4,250,445; 4,808,908; RE30586.
REV. B
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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD674B/AD774B--SPECIFICATIONS (T
VLOGIC = +5 V 10%, VEE = -15 V 10% or -12 V
Model (AD674B or AD774B) RESOLUTION LINEARITY ERROR @ +25C TMIN to TMAX DIFFERENTIAL LINEARITY ERROR (Minimum Resolution for Which No Missing Codes are Guaranteed) UNIPOLAR OFFSET1 @ +25C BIPOLAR OFFSET @ +25C FULL-SCALE CALIBRATION ERROR1, 2 @ +25C (with Fixed 50 Resistor from REF OUT to REF IN) TEMPERATURE RANGE TEMPERATURE DRIFT (Using Internal Reference) Unipolar Bipolar Offset Full-Scale Calibration POWER SUPPLY REJECTION Max Change in Full-Scale Calibration VCC = 15 V 1.5 V or 12 V 0.6 V VLOGIC = 5 V 0.5 V VEE = -15 V 1.5 V or -12 V 0.6 V ANALOG INPUT Input Ranges Bipolar Unipolar Input Impedance 10 Volt Span 20 Volt Span POWER SUPPLIES Operating Range VLOGIC VCC VEE Operating Current ILOGIC ICC IEE POWER CONSUMPTION INTERNAL REFERENCE VOLTAGE 9.9 Output Current (Available for External Loads) (External Load Should Not Change During the Conversion)
3 1
MIN
to TMAX with VCC = +15 V
10% or +12 V
5%,
5% unless otherwise noted)
Min J Grade Typ Max 12 1 1 Min K Grade Typ Max 12 1/2 1/2
12 2 6 0.1 0 0.25 +70
12 2 3 0.1 0 0.125 +70
2 2 6
1 1 2
2 1/2 2
1 1/2 1
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
+4.5 +11.4 -16.5 3.5 3.5 10 220 175 10.0
+5.5 +16.5 -11.4 7 7 14 375 10.1 2.0
+4.5 +11.4 -16.5 3.5 3.5 10 220 175 9.9 10.0
+5.5 +16.5 -11.4 7 7 14 375 10.1 2.0
NOTES 1 Adjustable to zero. 2 Includes internal voltage reference error. 3 Maximum change from +25C value to the value at T MIN or TMAX. 4 Tested with REF OUT tied to REF IN through 50 resistor, VCC = +16.5 V, VEE = -16.5 V, VLOGIC = +5.5 V, and outputs in high-Z mode. 5 Tested with REF OUT tied to REF IN through 50 resistor, VCC = +12 V, V EE = -12 V, VLOGIC = +5 V, and outputs in high-Z mode. Specifications subject to change without notice. Specifications shown in boldface are tested on all devices at final electrical test at T MIN, +25C, and TMAX, and results from those tests are used to calculate outgoing quality levels. All min and max specifications are guaranteed, although only those shown in boldface are tested.
-2-
REV. B
AD674B/AD774B
Min A Grade Typ Max 12 1 1 12 2 6 0.1 -40 0.25 +85 -40 0.1 12 2 3 0.125 +85 -55 0.1 Min B Grade Typ Max 12 1/2 1/2 12 2 3 0.125 +125 Min T Grade Typ Max 12 1/2 1 Units Bits LSB LSB Bits LSB LSB % of FS C
2 2 8
1 1 5
1 2 7
LSB LSB LSB
2 1/2 2
1 1/2 1
1 1/2 1
LSB LSB LSB
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
Volts Volts Volts Volts k k
+4.5 +11.4 -16.5 3.5 3.5 10 220 175 9.9 10.0
+5.5 +16.5 -11.4 7 7 14 375 10.1 2.0
+4.5 +11.4 -16.5 3.5 3.5 10 220 175 9.9 10.0
+5.5 +16.5 -11.4 7 7 14 375 10.1 2.0
+4.5 +11.4 -16.5 3.5 3.5 10 220 175 9.9 10.0
+5.5 +16.5 -11.4 7 7 14 375 10.1 2.0
Volts Volts Volts mA mA mA mW4 mW5 Volts mA
REV. B
-3-
AD674B/AD774B DIGITAL SPECIFICATIONS
Parameter
(for all grades TMIN to TMAX with VCC = +15 V VEE = -15 V 10% or -12 V 5%)
Test Conditions
10% or +12 V
Min +2.0 -0.5 -10 -10
5%, VLOGIC = +5 V
Max VLOGIC +0.5 V +0.8 +10 +10 10
10%,
Units V V A A pF V V A pF
LOGIC INPUTS VIH High Level Input Voltage VIL Low Level Input Voltage IIH High Level Input Current IIL Low Level Input Current CIN Input Capacitance LOGIC OUTPUTS VOH High Level Output Voltage VOL Low Level Output Voltage IOZ High-Z Leakage Current COZ High-Z Output Capacitance
VIN = VLOGIC VIN = 0 V
IOH = 0.5 mA IOL = 1.6 mA VIN = 0 to VLOGIC
+2.4 -10 +0.4 +10 10
SWITCHING SPECIFICATIONS
CONVERTER START TIMING (Figure 1)
(for all grades TMIN to TMAX with VCC = +15 V 10% or +12 V 5%, VLOGIC = +5 V 10%, VEE = -15 V 10% or -12 V 5%; unless otherwise noted)
t HEC t SSC t HSC
CE
Parameter
Symbol
J, K, A, B Grades T Grade Min Typ Max Min Typ Max Units 6 9 4 6 50 50 50 50 50 0 50 8 12 5 7.3 10 15 6 8 200 6 9 4 6 50 50 50 50 50 0 50 8 12 5 7.3 10 15 6 8 225 s s s s ns ns ns ns ns ns ns ns
__
CS
_
Conversion Time 8-Bit Cycle (AD674B) tC 12-Bit Cycle (AD674B) tC 8-Bit Cycle (AD774B) tC 12-Bit Cycle (AD774B) tC STS Delay from CE tDSC CE Pulse Width tHEC CS to CE Setup tSSC CS Low During CE High tHSC tSRC R/C to CE Setup R/C LOW During CE High tHRC A0 to CE Setup tSAC A0 Valid During CE High tHAC
R/C
tSRC tHRC
A0
tSAC
t HAC
STS DB11 - DB0
t DSC
tC
HIGH IMPEDANCE
Figure 1. Convert Start Timing
CE CS _ R/C
t SSR
t HSR t HRR t HAR
READ TIMING--FULL CONTROL MODE (Figure 2)
J, K, A, B Grades T Grade Min Typ Max Min Typ Max Units 75 25 203 150 50 0 50 0 0 50 50 0 50 0 0 50
2
tSRR
Parameter Access Time CL = 100 pF Data Valid After CE Low Output Float Delay CS to CE Setup R/C to CE Setup A0 to CE Setup CS Valid After CE Low R/C High After CE Low A0 Valid After CE Low
Symbol tDD1 tHD tHL5 tSSR tSRR tSAR tHSR tHRR tHAR
A0 STS
t SAR
150 25 154
2
75
150
150
ns ns ns ns ns ns ns ns ns ns
t HD
HIGH IMPEDANCE
DATA VALID
DB11 - DB0
t DD
HIGH IMP.
t HL
Figure 2. Read Cycle Timing
+5V 3k DB N 3k 100pF DB N 100pF
NOTES 1 tDD is measured with the load circuit of Figure 3a and is defined as the time required for an output to cross 0.4 V or 2.4 V. 2 0C to TMAX. 3 At -40C. 4 At -55C. 5 tHL is defined as the time required for the data lines to change 0.5 V when loaded with the circuit of Figure 3b. Specifications shown in boldface are tested on all devices at final electrical test with worst case supply voltages at TMIN, +25C, and TMAX. Results from those tests are used to calculate outgoing quality levels. All min and max specifications are guaranteed, although only those shown in boldface are tested. Specifications subject to change without notice.
High-Z to Logic 1
High-Z to Logic 0
Figure 3a. Load Circuit for Access Time Test
+5V 3k DB N 3k 10pF DB N 10pF
Logic 1 to High-Z
Logic 0 to High-Z
Figure 3b. Load Circuit for Output Float Delay Test
-4-
REV. B
AD674B/AD774B
TIMING--STAND-ALONE MODE (Figures 4a and 4b)
Parameter Data Access Time Low R/C Pulse Width STS Delay from R/C Data Valid After R/C Low STS Delay After Data Valid High R/C Pulse Width Symbol tDDR tHRL tDS tHDR tHS tHRH J, K, A, B Grades T Grade Min Typ Max Min Typ Max Units 150 50 200 25 30 150 200 600 50 225 25 30 200 600 150 150 ns ns ns ns ns ns
R/C
t HRL
t DS
STS
tC t HDR
DATA DB11_ DB0 VALID
t DS
t HS
HIGH-Z DATA VALID
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
VCC to Digital Common . . . . . . . . . . . . . . . . . . . 0 to +16.5 V VEE to Digital Common . . . . . . . . . . . . . . . . . . . . . 0 to -16.5 V VLOGIC to Digital Common . . . . . . . . . . . . . . . . . . . . 0 to +7 V Analog Common to Digital Common . . . . . . . . . . . . . . . 1 V Digital Inputs to Digital Common . . . -0.5 V to VLOGIC +0.5 V Analog Inputs to Analog Common . . . . . . . . . . . . . VEE to VCC 20 VIN to Analog Common . . . . . . . . . . . . . . . . . . . . . . 24 V REF OUT . . . . . . . . . . . . . . . . . . Indefinite Short to Common . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Momentary Short to VCC Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . +175C Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825 mW Lead Temperature, Soldering . . . . . . . . . . . . . . 300C, 10 sec Storage Temperature . . . . . . . . . . . . . . . . . . . -65C to +150C
*Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and 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.
Flgure 4a. Stand-Alone Mode Timing Low Pulse R/C
R/C
t HRH
STS
t DS tC t HDR
DATA VALID HIGH-Z
t DDR
DB11_ DB0 HIGH-Z
t HL
Figure 4b. Stand-Alone Mode Timing High Pulse for R/C
ORDERING GUIDE
Modell AD674BJN AD674BKN AD674BJR AD674BKR AD674BAD AD674BBD AD674BTD AD774BJN AD774BKN AD774BJR AD774BKR AD774BAD AD774BBD AD774BTD
Temperature 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C
Conversion Time (max) 15 s 15 s 15 s 15 s 15 s 15 s 15 s 8 s 8 s 15 s 15 s 8 s 8 s 8 s
INL (TMIN to TMAX) 1 LSB 1/2 LSB 1 LSB 1/2 LSB 1 LSB 1/2 LSB 1 LSB 1 LSB 1/2 LSB 1 LSB 1/2 LSB 1 LSB 1/2 LSB 1 LSB
Package Description Plastic DIP Plastic DIP Plastic SOIC Plastic SOIC Ceramic DIP Ceramic DIP Ceramic DIP Plastic DIP Plastic DIP Plastic SOIC Plastic SOIC Ceramic DIP Ceramic DIP Ceramic DIP
Package Option2 N-28 N-28 R-28 R-28 D-28 D-28 D-28 N-28 N-28 R-28 R-28 D-28 D-28 D-28
NOTES 1 For details on grade and package offerings screened in accordance with MIL-STD-883, refer to the Analog Devices Military Products Databook or current AD674B/ AD774B/883B data sheet. 2 N = Plastic DIP; D = Hermetic DIP; R = Plastic SOIC.
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 the AD674B/AD774B 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.
WARNING!
ESD SENSITIVE DEVICE
REV. B
-5-
AD674B/AD774B
DEFINITION OF SPECIFICATIONS
LINEARITY ERROR Linearity error refers to the deviation of each individual code from a line drawn from "zero" through "full scale." The point used as "zero" occurs 1/2 LSB (1.22 mV for 10 volt span) before the first code transition (all zeroes to only the LSB "on"). "Full scale" is defined as a level 1 1/2 LSB beyond the last code transition (to all ones). The deviation of a code from the true straight line is measured from the middle of each particular code. The K, B. and T grades are guaranteed for maximum nonlinearity of 1/2 LSB. For these grades, this means that an analog value which falls exactly in the center of a given code width will result in the correct digital output code. Values nearer the upper or lower transition of the code width may produce the next upper or lower digital output code. The J and A grades are guaranteed to 1 LSB max error. For these grades, an analog value which falls within a given code width will result in either the correct code for that region or either adjacent one. Note that the linearity error is not user adjustable. DIFFERENTIAL LINEARITY ERROR (NO MISSING CODES) A specification which guarantees no missing codes requires that every code combination appear in a monotonic increasing sequence as the analog input level is increased. Thus every code must have a finite width. The AD674B and AD774B guarantee no missing codes to 12-bit resolution, requiring that all 4096 codes must be present over the entire operating temperature ranges. UNIPOLAR OFFSET The first transition should occur at a level 1/2 LSB above analog common. Unipolar offset is defined as the deviation of the actual transition from that point. This offset can be adjusted as discussed later. The unipolar offset temperature coefficient specifies the maximum change of the transition point over temperature, with or without external adjustment. BIPOLAR OFFSET In the bipolar mode the major carry transition (0111 1111 1111 to 1000 0000 0000) should occur for an analog value 1/2 LSB below analog common. The bipolar offset error and temperature coefficient specify the initial deviation and maximum change in the error over temperature.
QUANTIZATION UNCERTAINTY Analog-to-digital converters exhibit an inherent quantization uncertainty of 1/2 LSB. This uncertainty is a fundamental characteristic of the quantization process and cannot be reduced for a converter of given resolution. LEFT-JUSTIFIED DATA The output data format is left-justified. This means that the data represents the analog input as a fraction of full scale, ranging from 0 to 4095/4096. This implies a binary point 4095 to the left of the MSB. FULL-SCALE CALIBRATION ERROR The last transition (from 1111 1111 1110 to 1111 1111 1111) should occur for an analog value 1 1/2 LSB below the nominal full scale (9.9963 volts for 10.000 volts full scale). The full-scale calibration error is the deviation of the actual level at the last transition from the ideal level. This error, which is typically 0.05 to 0.1% of full scale, can be trimmed out as shown in Figures 7 and 8. The full-scale calibration error over temperature is given with and without the initial error trimmed out. The temperature coefficients for each grade indicate the maximum change in the full-scale gain from the initial value using the internal 10 V reference. TEMPERATURE DRIFT The temperature drift for full-scale calibration, unipolar offset, and bipolar offset specifies the maximum change from the initial (+25C) value to the value at TMIN or TMAX. POWER SUPPLY REJECTION The standard specifications assume use of +5.00 V and 15.00 V or 12.00 V supplies. The only effect of power supply error on the performance of the device will be a small change in the full-scale calibration. This will result in a linear change in all low-order codes. The specifications show the maximum fullscale change from the initial value with the supplies at the various limits. CODE WIDTH A fundamental quantity for A/D converter specifications is the code width. This is defined as the range of analog input values for which a given digital output code will occur. The nominal value of a code width is equivalent to 1 least significant bit (LSB) of the full-scale range or 2.44 mV out of 10 volts for a 12-bit ADC.
-6-
REV. B
AD674B/AD774B
AD674B AND AD774B PIN DESCRIPTION
Symbol AGND A0
Pin No. 9 4
Type Name and Function P DI Analog Ground (Common). Byte Address/Short Cycle. If a conversion is started with A0 Active LOW, a full 12-bit conversion cycle is initiated. If A0 is Active HIGH during a convert start, a shorter 8-bit conversion cycle results. During Read (R/C = 1) with 12/8 LOW, A0 = LOW enables the 8 most significant bits, and A0 = HIGH enables DB3-DB0 and sets DB7-DB4 = 0. Bipolar Offset. Connect through a 50 resistor to REF OUT for bipolar operation or to Analog Common for unipolar operation. Chip Enable. Chip Enable is Active HIGH and is used to initiate a convert or read operation. Chip Select. Chip Select is Active LOW. Data Bits 11 through 8. In the 12-bit format (see 12/8 and A0 pins), these pins provide the upper 4 bits of data. In the 8-bit format, they provide the upper 4 bits when A0 is LOW and are disabled when A0 is HIGH. Data Bits 7 through 4. In the 12-bit format these pins provide the middle 4 bits of data. In the 8-bit format they provide the middle 4 bits when A0 is LOW and all zeroes when A0 is HIGH. Data Bits 3 through 0. In both the 12-bit and 8-bit format these pins provide the lower 4 bits of data when A0 is HIGH; they are disabled when A0 is LOW. Digital Ground (Common). +10 V Reference Output. Read/Convert. In the full control mode R/C is Active HIGH for a read operation and Active LOW for a convert operation. In the stand-alone mode, the falling edge of R/C initiates a conversion. Reference Input is connected through a 50 resistor to +10 V Reference for normal operation. Status is Active HIGH when a conversion is in progress and goes LOW when the conversion is completed. +12 V/+15 V Analog Supply. -12 V/-15 V Analog Supply. +5 V Logic Supply. 10 V Span Input, 0 to +10 V unipolar mode or -5 V to +5 V bipolar mode. When using the 20 V Span, 10 VIN should not be connected. 20 V Span Input, 0 to +20 V unipolar mode or -10 V to +10 V bipolar mode. When using the 10 V Span, 20 VIN should not be connected. The 12/8 pin determines whether the digital output data is to be organized as two 8-bit words (12/8 LOW) or a single 12-bit word (12/8 HIGH).
PIN CONFIGURATION
VLOGIC
_
BIP OFF CE CS
12 6 3
AI DI DI DO
DB11-DB8 27-24
DB7-DB4 DB3-DB0 DGND REF OUT R/C REF IN STS VCC VEE VLOGIC 10 VIN 20 VIN 12/8
23-20 19-16 15 8 5 10 28 7 11 1 13 14 2
DO DO P AO DI AI DO P P P AI AI DI
TYPE: AI = AO = DI = DO = P=
Analog Input Analog Output Digital Input Digital Output Power
1
28 STS 27 DB11 (MSB) 26 DB10 25 DB9
12/8 2
__
CS A0
_
3 4 5
R/C
CE 6 VCC REF OUT AGND 7 8 9
AD674B or AD774B
24 DB8 23 DB7 22 DB6
21 DB5 TOP VIEW 20 DB4 (Not to Scale) 19 DB3 18 DB2 17 DB1 16 DB0 (LSB) 15 DGND
REF IN 10 VEE 11 BIP OFF 12 10VIN 20VIN 13 14
REV. B
-7-
AD674B/AD774B
CIRCUIT OPERATION
The AD674B and AD774B are complete 12-bit monolithic A/D converters which require no external components to provide the complete successive-approximation analog-to-digital conversion function. A block diagram is shown in Figure 5.
+5V SUPPLY V LOGIC DATA MODE SELECT 12/8 CHIP SELECT CS BYTE ADDRESS/ SHORT CYCLE A0 READ/ CONVERT R/C CHIP ENABLE CE +12/+15V SUPPLY
mately a 1 MHz rate. Thus it is important to recognize that the signal source driving the ADC must be capable of holding a constant output voltage under dynamically-changing load conditions.
1
28
STATUS STS DB11 (MSB) DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 (LSB) DIGITAL COMMON DC DIGITAL DATA OUTPUTS
2
3 CONTROL
MSB
3 S T A T E N Y B B L E A O U T P U T B U F F E R S N Y B B L E B
27 26 25 24 23 22
4 5 6 7
I DAC CLOCK SAR COMP
12 12
VCC
+10V REFERENCE REF OUT ANALOG COMMON AC REFERENCE INPUT REF IN __ 12/ 15V SUPPLY V EE BIPOLAR OFFSET BIPOFF 10V SPAN INPUT 10V IN 20V SPAN INPUT 20V IN
8 9
10
10V REF IREF 19.95k
21
20 19 18 17 16 15
11 12 13 14 DAC VOLTAGE DIVIDER N
12
VEE
N Y B B L E C
Figure 6. Op Amp--ADC Interface
LSB
AD674B/AD774B
Figure 5. Block Diagram of AD674B and AD774B
When the control section is commanded to initiate a conversion (as described later), it enables the clock and resets the successive-approximation register (SAR) to all zeroes. Once a conversion cycle has begun, it cannot be stopped or restarted and data is not available from the output buffers. The SAR, timed by the clock, will sequence through the conversion cycle and return an end-of-convert flag to the control section. The control section will then disable the clock, bring the output status flag low, and enable control functions to allow data read by external command. During the conversion cycle, the internal 12-bit current output DAC is sequenced by the SAR from the most-significant-bit (MSB) to least-significant-bit (LSB) to provide an output current which accurately balances the input signal current through the divider network. The comparator determines whether the addition of each successively-weighted bit current causes the DAC current sum to be greater or less than the input current; if the sum is less, the bit is left on; if more, the bit is turned off. After testing all the bits, the SAR contains a 12-bit binary code which accurately represents the input signal to within 1/2 LSB. The temperature-compensated reference provides the primary voltage reference to the DAC and guarantees excellent stability with both time and temperature. The reference is trimmed to 10.00 volts 1%; it can supply up to 2.0 mA to an external load in addition to the requirements of the reference input resistor (0.5 mA) and bipolar offset resistor (0.5 mA). Any external load on the reference must remain constant during conversion. The thin film application resistors are trimmed to match the fullscale output current of the DAC. The input divider network provides a 10 V or 20 V input range. The bipolar offset resistor is grounded for unipolar operation and connected to the 10 volt reference for bipolar operation.
DRIVING THE ANALOG INPUT
The closed-loop output impedance of an op amp is equal to the openloop output impedance (usually a few hundred ohms) divided by the loop gain at the frequency of interest. It is often assumed that the loop gain of a follower-connected op amp is sufficiently high to reduce the closed-loop output impedance to a negligibly small value, particularly if the signal is low frequency. However, the amplifier driving the ADC must either have sufficient loop gain at 1 MHz to reduce the closed-loop output impedance to a low value or have low open-loop output impedance. This can be accomplished by using a wideband op amp, such as the AD711. If a sample-hold amplifier is required, the monolithic AD585 or AD781 is recommended, with the output buffer driving the AD674B or AD774B input directly. A better alternative is the AD1674 which is a 10 s sampling ADC in the same pinout as the AD574A, AD674A or AD774B and is functionally equivalent.
SUPPLY DECOUPLING AND LAYOUT CONSIDERATION
It is critically important that the power supplies be filtered, well regulated, and free from high frequency noise. Use of noisy supplies will cause unstable output codes. Switching power supplies are not recommended for circuits attempting to achieve 12-bit accuracy unless great care is used in filtering any switching spikes present in the output. Few millivolts of noise represent several counts of error in a 12-bit ADC. Decoupling capacitors should be used on all power supply pins; the +5 V supply decoupling capacitor should be connected directly from Pin 1 to Pin 15 (digital common) and the +VCC and -VEE pins should be decoupled directly to analog common (Pin 9). A suitable decoupling capacitor is a 4.7 F tantalum type in parallel with a 0.1 F ceramic disc type. Circuit layout should attempt to locate the ADC, associated analog input circuitry, and interconnections as far as possible from logic circuitry. For this reason, the use of wire-wrap circuit construction is not recommended. Careful printed-circuit layout and manufacturing is preferred.
The AD674B and AD774B are successive-approximation analogto-digital converters. During the conversion cycle, the ADC input current is modulated by the DAC test current at approxi-8-
REV. B
AD674B/AD774B
UNIPOLAR RANGE CONNECTIONS FOR THE AD674B AND AD774B
The AD674B and AD774B contain all the active components required to perform a complete 12-bit A/D conversion. Thus, for most situations, all that is necessary is connection of the power supplies (+5 V, +12/+15 V and -12/-15 V), the analog input, and the conversion initiation command, as discussed on the next page.
If Pin 12 is connected to Pin 9, the unit will behave in this manner, within specifications. If the offset trim (R1) is used, it should be trimmed as above, although a different offset can be set for a particular system requirement. This circuit will give approximately 15 mV of offset trim range. The full-scale trim is done by applying a signal 1 1/2 LSB below the nominal full scale (9.9963 for a 10 V range). Trim R2 to give the last transition (1111 1111 1110 to 1111 1111 1111).
BIPOLAR OPERATION
The connections for bipolar ranges are shown in Figure 8. Again, as for the unipolar ranges, if the offset and gain specifications are sufficient, one or both of the trimmers shown can be replaced by a 50 1% fixed resistor. The analog input is applied as for the unipolar ranges. Bipolar calibration is similar to unipolar calibration. First, a signal 1/2 LSB above negative full scale (-4.9988 V for the 5 V range) is applied and R1 is trimmed to give the first transition (0000 0000 0000 to 0000 0000 0001). Then a signal 1 1/2 LSB below positive full scale (+4.9963 V for the 5 V range) is applied and R2 trimmed to give the last transition (1111 1111 1110 to 1111 1111 1111).
Figure 7. Unipolar Input Connections
All of the thin-film application resistors of the AD674B and AD774B are factory trimmed for absolute calibration. Therefore, in many applications, no calibration trimming will be required. The absolute accuracy for each grade is given in the specification tables. For example, if no trims are used, 2 LSB max zero offset error and 0.25% (10 LSB) max full-scale error are guaranteed. If the offset trim is not required, Pin 12 can be connected directly to Pin 9; the two resistors and trimmer for Pin 12 are then not needed. If the full-scale trim is not required, a 50 1% metal film resistor should be connected between Pin 8 and Pin 10. The analog input is connected between Pins 13 and 9 for a 0 to +10 V input range, between Pins 14 and 9 for a 0 to +20 V input range. Input signals beyond the supplies are easily accommodated. For the 10 volt span input, the LSB has a nominal value of 2.44 mV; for the 20 volt span, 4.88 mV. If a 10.24 V range is desired (nominal 2.5 mV/bit), the gain trimmer (R2) should be replaced by a 50 resistor, and a 200 trimmer inserted in series with the analog input to Pin 13 (for a full-scale range of 20.48 V (5 mV/bit), use a 500 trimmer into Pin 14). The gain trim described below is now done with these trimmers. The nominal input impedance into Pin 13 is 5 k, and 10 k into Pin 14.
UNIPOLAR CALIBRATION
Figure 8. Bipolar Input Connections
GROUNDING CONSIDERATIONS
The analog common at Pin 9 is the ground reference point for the internal reference and is thus the "high quality" ground for the ADC; it should be connected directly to the analog reference point of the system. In order to achieve the high accuracy performance available from the ADC in an environment of high digital noise content, it is required that the analog and digital commons be connected together at the package. In some situations, the digital common at Pin 15 can be connected to the most convenient ground reference point; digital power return is preferred.
The connections for unipolar ranges are shown in Figure 7. The AD674B or AD774B is trimmed to a nominal 1/2 LSB offset so that the exact analog input for a given code will be in the middle of that code (halfway between the transitions to the codes above and below it). Thus, when properly calibrated, the first transition (from 0000 0000 0000 to 0000 0000 0001) will occur for an input level of +1/2 LSB (1.22 mV for 10 V range).
REV. B
-9-
AD674B/AD774B
VALUE OF A 0 AT LAST CONVERT COMMAND Q D EN D EN EOC 12 EOC 8
START CONVERT R S
Q
S R
Q QB
SAR RESET
CE HIGH IF CONVERSION IN PROGRESS CS CLK EN
R/C
STATUS NYBBLE A ENABLE NYBBLE B ENABLE NYBBLE C ENABLE
A0 READ
TO OUTPUT BUFFERS
12/8
NYBBLE B = 0 ENABLE
Figure 9. Equivalent Internal Logic Circuitry
CONTROL LOGIC
Table I. Truth Table
The AD674B and AD774B contain on-chip logic to provide conversion initiation and data read operations from signals commonly available in microprocessor systems; this internal logic circuitry is shown in Figure 9. The control signals CE, CS, and R/C control the operation of the converter. The state of R/C when CE and CS are both asserted determines whether a data read (R/C = 1) or a convert (R/C = 0) is in progress. The register control inputs A0 and 12/8 control conversion length and data format. If a conversion is started with A0 low, a full 12-bit conversion cycle is initiated. If A0 is high during a convert start, a shorter 8-bit conversion cycle results. During data read operations, A0 determines whether the three-state buffers containing the 8 MSBs of the conversion result (A0 = 0) or the 4 LSBs (A0 = 1) are enabled. The 12/8 pin determines whether the output data is to be organized as two 8-bit words (12/8 tied to DIGITAL COMMON) or a single 12-bit word (12/8 tied to VLOGIC). In the 8-bit mode, the byte addressed when A0 is high contains the 4 LSBs from the conversion followed by four trailing zeroes. This organization allows the data lines to be overlapped for direct interface to 8-bit buses without the need for external three-state buffers. An output signal, STS, indicates the status of the converter. STS goes high at the beginning of a conversion and returns low when the conversion cycle is complete.
CE CS 0 X 1 1 1 1 1 X 1 0 0 0 0 0
R/C 12/8 A0 Operation X X 0 0 1 1 1 X X X X 1 0 0 X X 0 1 X 0 1 None None Initiate 12-Bit Conversion Initiate 8-Bit Conversion Enable 12-Bit Parallel Output Enable 8 Most Significant Bits Enable 4 LSBs +4 Trailing Zeroes
The ADC may be operated in one of two modes, the full-control mode and the stand-alone mode. The full-control mode utilizes all the control signals and is useful in systems that address decode multiple devices on a single data bus. The stand-alone mode is useful in systems with dedicated input ports available. In general, the stand-alone mode is capable of issuing start-convert commands on a more precise basis and, therefore, produces higher accuracy results. The following sections describe these two modes in more detail.
FULL-CONTROL MODE
Chip Enable (CE), Chip Select (CS) and Read/Convert (R/C) are used to control Convert or Read modes of operation. Either CE or CS may be used to initiate a conversion. The state of R/C -10- REV. B
AD674B/AD774B
when CE and CS are both asserted determines whether a data Read (R/C = 1) or a Convert (R/C = 0) is in progress. R/C should be LOW before both CE and CS are asserted; if R/C is HIGH, a Read operation will momentarily occur, possibly resulting in system bus contention.
STAND-ALONE MODE GENERAL A/D CONVERTER INTERFACE CONSIDERATIONS
"Stand-alone" mode is useful in systems with dedicated input ports available and thus not requiring full bus interface capability. Stand-alone mode applications are generally able to issue conversion start commands more precisely than full-control mode, resulting in improved accuracy. CE and 12/8 are wired HIGH, CS and A0 are wired LOW, and conversion is controlled by R/C. The three-state buffers are enabled when R/C is HIGH and a conversion starts when R/C goes LOW. This gives rise to two possible control signals--a high pulse or a low pulse. Operation with a low pulse is shown in Figure 4a. In this case, the outputs are forced into the high impedance state in response to the falling edge of R/C and return to valid logic levels after the conversion cycle is completed. The STS line goes HIGH 200 ns after R/C goes LOW and returns low 600 ns after data is valid. If conversion is initiated by a high pulse as shown in Figure 4b, the data lines are enabled during the time when R/C is HIGH. The falling edge of R/C starts the next conversion, and the data lines return to three-state (and remain three-state) until the next high pulse of R/C.
CONVERSION TIMING
A typical A/ D converter interface routine involves several operations. First, a write to the ADC address initiates a conversion. The processor must then wait for the conversion cycle to complete, since most integrated circuit ADCs take longer than one instruction cycle to complete a conversion. Valid data can, of course, only be read after the conversion is complete. The AD674B and AD774B provide an output signal (STS) which indicates when a conversion is in progress. This signal can be polled by the processor by reading it through an external threestate buffer (or other input port). The STS signal can also be used to generate an interrupt upon completion of conversion if the system timing requirements are critical and the processor has other tasks to perform during the ADC conversion cycle. Another possible time-out method is to assume that the ADC will take its maximum conversion time to convert, and insert a sufficient number of "no-op" instructions to ensure that this amount of processor time is consumed. Once conversion is complete, the data can be read. For converters with more data bits than are available on the bus, a choice of data formats is required, and multiple read operations are needed. The AD674B and AD774B include internal logic to permit direct interface to 8-bit and 16-bit data buses, selected by the 12/8 input. In 16-bit bus applications (12/8 high) the data lines (DB11 through DB0) may be connected to either the 12 most significant or 12 least significant bits of the data bus. The remaining four bits should be masked in software. The interface to an 8-bit data bus (12/8 low) is done in a left-justified format. The even address (A0 low) contains the 8 MSBs (DB11 through DB4). The odd address (A0 high) contains the 4 LSBs (DB3 through DB0) in the upper half of the byte, followed by four trailing zeroes, thus eliminating bit masking instructions. It is not possible to rearrange the output data lines for right-justified 8-bit bus interface.
D7 XXX0 DB11 (EVEN ADDR) (MSB) DB10 XXX1 (ODD ADDR) DB9 DB8 DB7 DB6 DB5 D0 DB4
Once a conversion is started, the STS line goes HIGH. Convert start commands will be ignored until the conversion cycle is complete. The output data buffers can be enabled up to 1.2 s prior to STS going LOW. The STS line will return LOW at the end of the conversion cycle. The register control inputs, A0 and 12/8, control conversion length and data format. If a conversion is started with A0 LOW, a full 12-bit conversion cycle is initiated. If A0 is HIGH during a convert start, a shorter 8-bit conversion cycle results. During data read operations, A0 determines whether the threestate buffers containing the 8 MSBs of the conversion result (A0 = 0) or the 4 LSBs (A0 = 1) are enabled. The 12/8 pin determines whether the output data is to be organized as two 8-bit words (12/8 tied LOW) or a single 12-bit word (12/8 tied HIGH). In the 8-bit mode, the byte addressed when A0 is high contains the 4 LSBs from the conversion followed by four trailing zeroes. This organization allows the data lines to be overlapped for direct interface to 8-bit buses without the need for external three-state buffers.
DB3
DB2
DB1
DB0 (LSB)
0
0
0
0
Figure 10. Data Format for 8-Bit Bus
REV. B
-11-
AD674B/AD774B
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Pin Ceramic DIP Package (D-28)
C1536-24-7/91
0.05 (1.27) 0.045 (1.14) 15 0.59 + 0.01 - (14.98) 1 0.085 (2.16) 1.42 (36.07) 1.40 (35.56) 14 0.095 (2.41) 30
o
0.050 (12.83) 28
0.08 (2.0)
SEATING PLANE
0.125 MIN (3.17) 0.145 + 0.02 - (3.68)
0.017 + 0.003 - (0.43)
0.1 (2.54)
0.050 + 0.010 - (1.27) 0.047 + 0.007 - (1.19)
0.010 + 0.002 - (0.254 + 0.05) - 0.6 (15.24)
28-Lead Plastic DIP Package (N-28A)
28 15 0.550 (13.97) 0.530 (13.462) 0.200 (5.080) MAX 1 1.450 (36.83) 1.440 (36.576) 14 0.606 (15.39) 0.594 (15.09) 0.160 (4.06) 0.140 (3.56) 15 o 0
o
0.020 (0.508) 0.015 (0.381)
0.105 (2.67) 0.095 (2.41)
0.065 (1.65) 0.045 (1.14)
0.175 (4.45) 0.120 (3.05)
0.012 (0.305) 0.008 (0.203)
LEADS ARE SOLDER DIPPED OR TIN - PLATED ALLOY 42 OR COPPER.
-12-
REV. B
PRINTED IN U.S.A.

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