AD670

AD670 Low Cost Signal Conditioning 8-Bit ADC

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Technical content

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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. a Low Cost Signal Conditioning 8-Bit ADC AD670

FEATURES

Complete 8-Bit Signal Conditioning A/D Converter Including Instrumentation Amp and Reference Microprocessor Bus Interface 10 ms Conversion Speed Flexible Input Stage: Instrumentation Amp Front End Provides Differential Inputs and High Common-Mode Rejection No User Trims Required No Missing Codes Over Temperature Single +5 V Supply Operation Convenient Input Ranges 20-Pin DIP or Surface-Mount Package Low Cost Monolithic Construction MIL-STD-883B Compliant Versions Available GENERAL DESCRIPTION The AD670 is a complete 8-bit signal conditioning analog- to-digital converter. It consists of an instrumentation amplifier front end along with a DAC, comparator, successive approxima- tion register (SAR), precision voltage reference, and a three- state output buffer on a single monolithic chip. No external components or user trims are required to interface, with full accuracy, an analog system to an 8-bit data bus. The AD670 will operate on the +5 V system supply. The input stage pro- vides differential inputs with excellent common-mode rejection and allows direct interface to a variety of transducers. The device is configured with input scaling resistors to permit two input ranges: 0 mV to 255 mV (1 mV/LSB) and 0 to 2.55 V (10 mV/LSB). The AD670 can be configured for both unipolar and bipolar inputs over these ranges. The differential inputs and common-mode rejection of this front end are useful in applica- tions such as conversion of transducer signals superimposed on common-mode voltages. The AD670 incorporates advanced circuit design and proven processing technology. The successive approximation function is implemented with I 2L (integrated injection logic). Thin-film SiCr resistors provide the stability required to prevent missing codes over the entire operating temperature range while laser wafer trimming of the resistor ladder permits calibration of the device to within ± 1 LSB. Thus, no user trims for gain or offset are required. Conversion time of the device is 10 µs. The AD670 is available in four package types and five grades. The J and K grades are specified over 0 °C to +70°C and come in 20-pin plastic DIP packages or 20-terminal PLCC packages. The A and B grades (–40°C to +85°C) and the S grade (–55°C to +125°C) come in 20-pin ceramic DIP packages. Tel: 617/329-4700 Fax: 617/326-8703 The S grade is also available with optional processing to MIL-STD-883 in 20-pin ceramic DIP or 20-terminal LCC packages. The Analog Devices Military Products Databook should be consulted for detailed specifications. PRODUCT HIGHLIGHTS 1. The AD670 is a complete 8-bit A/D including three-state outputs and microprocessor control for direct connection to 8-bit data buses. No external components are required to perform a conversion. 2. The flexible input stage features a differential instrumenta- tion amp input with excellent common-mode rejection. This allows direct interface to a variety of transducers without preamplification. 3. No user trims are required for 8-bit accurate performance. 4. Operation from a single +5 V supply allows the AD670 to run off of the microprocessor’s supply. 5. Four convenient input ranges (two unipolar and two bipolar) are available through internal scaling resistors: 0 mV to 255 mV (1 mV/LSB) and 0 V to 2.55 V (10 mV/LSB). 6. Software control of the output mode is provided. The user can easily select unipolar or bipolar inputs and binary or 2s complement output codes.

Min Typ Max Min Typ Max Units OPERATING TEMPERATURE RANGE 0 +70 0 +70 °C RESOLUTION 8 8 Bit CONVERSION TIME 10 10 µs RELATIVE ACCURACY 61/2 61/4 LSB TMIN to TMAX 6l/2 61/2 LSB DIFFERENTIAL LINEARITY ERROR 1 TMIN to TMAX GUARANTEED NO MISSING CODES ALL GRADES GAIN ACCURACY @ +25°C 61.5 60.75 LSB TMIN to TMAX 62.0 61.0 LSB UNIPOLAR ZERO ERROR @ +25°C 61.5 60.75 LSB TMIN to TMAX 62.0 61.0 LSB BIPOLAR ZERO ERROR @ +25°C 61.5 60.75 LSB TMIN to TMAX 62.0 61.0 LSB ANALOG INPUT RANGES DIFFERENTIAL (–VIN to +VIN) Low Range 0 to +255 0 to +255 mV –128 to +127 –128 to +127 mV High Range 0 to +2.55 0 to +2.55 V ABSOLUTE (Inputs to Power GND) Low Range TMIN to TMAX –0.150 V CC – 3.4 –0.150 V CC – 3.4 V High Range TMIN to TMAX –1.50 V CC –1.50 V CC V BIAS CURRENT (255 mV RANGE) TMIN to TMAX 200 500 200 500 nA OFFSET CURRENT (255 mV RANGE) TMIN to TMAX 40 200 40 200 nA

2.55 V RANGE FULL-SCALE MATCH

+ AND – INPUT ± 1/2 ± 1/2 LSB COMMON-MODE REJECTION RATIO (255 mV RANGE) 11 LSB COMMON-MODE REJECTION RATIO (2.55 V RANGE) 1 1 LSB POWER SUPPLY Operating Range 4.5 5.5 4.5 5.5 V Current ICC 30 45 30 45 mA Rejection Ratio T MIN to TMAX 0.015 0.015 % of FS/% DIGITAL OUTPUTS SINK CURRENT (V OUT = 0.4 V) TMIN to TMAX 1.6 1.6 mA SOURCE CURRENT (V OUT = 2.4 V) TMIN to TMAX 0.5 0.5 mA THREE-STATE LEAKAGE CURRENT 640 640 µA OUTPUT CAPACITANCE 5 5 pF DIGITAL INPUT VOLTAGE VINL 0.8 0.8 V VINH 2.0 2.0 V DIGITAL INPUT CURRENT (0 ≤ VIN ≤ +5 V) IINL –100 –100 µA IINH +100 +100 µA INPUT CAPACITANCE 10 10 pF NOTES 1Tested at V CC = 4 5 V, 5.0 V and 5.5 V. Specifications shown in boldface are tested on all production units at final electrical test. 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 on all production units. Specifications subject to change without notice. AD670–SPECIFICATIONS (@ VCC = +5 V and +258C, unless otherwise noted) REV. A–2–

Model AD670A AD670B AD670S Min Typ Max Min Typ Max Min Typ Max Units OPERATING TEMPERATURE RANGE –40 +85 –40 +85 –55 +125 °C RESOLUTION 8 8 8 Bit CONVERSION TIME 10 10 10 µs RELATIVE ACCURACY 61/2 61/4 61/2 LSB TMIN to TMAX 61/2 61/2 61 LSB DIFFERENTIAL LINEARITY ERROR 1 TMIN to TMAX GUARANTEED NO MISSING CODES ALL GRADES GAIN ACCURACY @ +25°C 61.5 60.75 61.5 LSB TMIN to TMAX 62.5 61.5 62.5 LSB UNIPOLAR ZERO ERROR @ +25°C 61.0 60.5 61.0 LSB TMIN to TMAX 62.0 61.0 62.0 LSB BIPOLAR ZERO ERROR @ +25°C 61.0 60.5 61.0 LSB TMIN to TMAX 62.0 61.0 62.0 LSB ANALOG INPUT RANGES DIFFERENTIAL ( –VIN to +VIN) Low Range 0 to +255 0 to +255 0 to +255 mV –128 to +127 –128 to +127 –128 to +127 mV High Range 0 to +2.55 0 to +2.55 0 to +2.55 V ABSOLUTE (Inputs to Power GND) High Range TMIN to TMAX –1.50 VCC –1.50 VCC –1.50 VCC V BIAS CURRENT (255 mV RANGE) TMIN to TMAX 200 500 200 500 200 750 nA OFFSET CURRENT (255 mV RANGE) TMIN to TMAX 40 200 40 200 40 200 nA + AND – INPUT ± 1/2 ± 1/2 ± 1/2 LSB COMMON-MODE REJECTION RATIO (255 mV RANGE) 11 1 LSB COMMON-MODE REJECTION RATIO (2.55 V RANGE) 1 1 1 LSB POWER SUPPLY Current ICC 30 45 30 45 30 45 mA Rejection Ratio T MIN to TMAX 0.015 0.015 0.015 % of FS/% DIGITAL OUTPUTS SINK CURRENT (V OUT = 0.4 V) TMIN to TMAX 1.6 1.6 1.6 mA SOURCE CURRENT (V OUT = 2.4 V) TMIN to TMAX 0.5 0.5 0.5 mA THREE-STATE LEAKAGE CURRENT 640 640 640 µA OUTPUT CAPACITANCE 5 5 5 pF DIGITAL INPUT VOLTAGE VINL 0.8 0.8 0.7 V VINH 2.0 2.0 2.0 V DIGITAL INPUT CURRENT (0 ≤ VIN ≤ +5 V) IINL –100 –100 –100 µA IINH +100 +100 + 100 µA INPUT CAPACITANCE 10 10 10 pF NOTES Specifications shown in boldface are tested on all production units at final electrical test. 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 on all production units. Specifications subject to change without notice. AD670 REV. A –3–

2D = Ceramic DIP; N = Plastic DIP; P = Plastic Leaded Chip Carrier. Figure 1. AD670 Block Diagram and Terminal maximum rating conditions for extended periods may affect device reliability. to a variety of transducers. determined solely by the clock. No clock is used in the AD670. successive approximation design. CE or CS high during the valid data period ends the read cycle. cannot be stopped or restarted. ment; with a Logic 0, the output is offset binary.

Figure 17. Low Cost Sample-and-Hold Circuit for AD670 tween the two switches results in errors at the A/D. verted up to several kilohertz. The AD670 appears in Figure 18 interfaced to the IBM PC. Figure 18. IBM PC lnterface to AD670 when interfacing more than two AD670s to the I/O bus.

0 Unipolar Straight Binary

1 Bipolar Offset Binary

2 Unipolar 2s Complement

3 Bipolar 2s Complement

10 OUT & H310,1 ’INITIATE CONVERSION

20 ANALOGIN = INP (&H311) ’READ ANALOG INPUT

30 RETURN

Figure 19. Conversion Subroutine

REV. A–12– OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 20-Pin Plastic DIP (N-20) 20-Pin Ceramic DIP (D-20) 20-Terminal PLCC Package(P-20A) PIN 1 IDENTIFIER BOTTOM VIEW (PINS UP) 0.020 (0.50) R 0.021 (0.53) 0.290 (7.37) 0.032 (0.81) 0.026 (0.66) 0.180 (4.57) 0.165 (4.19) 0.040 (1.01) 0.025 (0.64) 0.056 (1.42) 0.042 (1.07) 0.025 (0.63) 0.015 (0.38) 0.110 (2.79) 0.085 (2.16) PIN 1 IDENTIFIER TOP VIEW (PINS DOWN) 0.395 (10.02) 0.385 (9.78)SQ 0.356 (9.04) 0.350 (8.89) SQ 0.048 (1.21) 0.042 (1.07) 0.048 (1.21) 0.042 (1.07)0.020 (0.50) R 0.050 (1.27) BSC C864c–2–4/89PRINTED IN U.S.A.