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Details, datasheet, quote on part number:AD670J
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Datasheet text preview:
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FEATURES Complete 8-Bit Signal Conditioning A/D Converter Including Instrumentation Amp and Reference Microprocessor Bus Interface 10 s 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
Low Cost Signal Conditioning 8-Bit ADC AD670
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The AD670 is a complete 8-bit signal conditioning analogto-digital converter. It consists of an instrumentation amplifier front end along with a DAC, comparator, successive approximation register (SAR), precision voltage reference, and a threestate 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 provides 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 applications 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 I2L (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. 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.
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 instrumentation 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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD670SPECIFICATIONS
Model
OPERATING TEMPERATURE RANGE RESOLUTION CONVERSION TIME RELATIVE ACCURACY TMIN to TMAX DIFFERENTIAL LINEARITY ERROR1 TMIN to TMAX GAIN ACCURACY @ +25°C TMIN to TMAX UNIPOLAR ZERO ERROR @ +25°C TMIN to TMAX BIPOLAR ZERO ERROR @ +25°C TMIN to TMAX ANALOG INPUT RANGES DIFFERENTIAL (VIN to +VIN) Low Range High Range ABSOLUTE (Inputs to Power GND) Low Range TMIN to TMAX High Range TMIN to TMAX BIAS CURRENT (255 mV RANGE) TMIN to TMAX OFFSET CURRENT (255 mV RANGE) TMIN to TMAX 2.55 V RANGE INPUT RESISTANCE 2.55 V RANGE FULL-SCALE MATCH + AND INPUT COMMON-MODE REJECTION RATIO (255 mV RANGE) COMMON-MODE REJECTION RATIO (2.55 V RANGE) POWER SUPPLY Operating Range C u r r e n t IC C Rejection Ratio TMIN to TMAX DIGITAL OUTPUTS SINK CURRENT (VOUT = 0.4 V) TMIN to TMAX SOURCE CURRENT (VOUT = 2.4 V) TMIN to TMAX THREE-STATE LEAKAGE CURRENT OUTPUT CAPACITANCE DIGITAL INPUT VOLTAGE V INL V INH DIGITAL INPUT CURRENT (0 VIN +5 V) IINL I INH INPUT CAPACITANCE
NOTES 1 Tested at VCC = 4 5 V, 5.0 V and 5.5 V.
(@ VCC = +5 V and +25 C, unless otherwise noted)
Min
0 8 10 1/2 l/2 GUARANTEED NO MISSING CODES ALL GRADES 1.5 2.0 1.5 2.0 1.5 2.0 0.75 1.0 0.75 1.0 0.75 1.0 LSB LSB LSB LSB LSB LSB
AD670J Typ
Max
+70
Min
0 8
AD670K Typ
Max
+70 10 1/4 1/2
Units
°C Bit µs LSB LSB
0 to +255 128 to +127 0 to +2.55 1.28 to +1.27 0.150 1.50 200 40 8.0 ± 1/2 1 1 4.5 30 5.5 45 0.015 4.5 VCC 3.4 V CC 500 200 12.0 8.0 0.150 1.50
0 to +255 128 to +127 0 to +2.55 1.28 to +1.27 VCC 3.4 V CC 200 40 500 200 12.0 ± 1/2 1 1 5.5 45 0.015
mV mV V V V V nA nA k LSB LSB LSB V mA % of FS/%
30
1.6 0.5 40 5 0.8 2.0
1.6 0.5 40 5 0.8 2.0
mA mA µA pF V V
100 +100 10
100 +100 10
µA µA pF
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.
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REV. A
AD670
Model Min
OPERATING TEMPERATURE RANGE RESOLUTION CONVERSION TIME RELATIVE ACCURACY TMIN to TMAX DIFFERENTIAL LINEARITY ERROR1 TMIN to TMAX GAIN ACCURACY @ +25°C TMIN to TMAX UNIPOLAR ZERO ERROR @ +25°C TMIN to TMAX BIPOLAR ZERO ERROR @ +25°C TMIN to TMAX ANALOG INPUT RANGES DIFFERENTIAL ( VIN to +VIN) Low Range High Range ABSOLUTE (Inputs to Power GND) Low Range TMIN to TMAX High Range TMIN to TMAX BIAS CURRENT (255 mV RANGE) TMIN to TMAX OFFSET CURRENT (255 mV RANGE) TMIN to TMAX 2.55 V RANGE INPUT RESISTANCE 2.55 V RANGE FULL-SCALE MATCH + AND INPUT COMMON-MODE REJECTION RATIO (255 mV RANGE) COMMON-MODE REJECTION RATIO (2.55 V RANGE) POWER SUPPLY Operating Range C u r r e n t IC C Rejection Ratio TMIN to TMAX DIGITAL OUTPUTS SINK CURRENT (VOUT = 0.4 V) TMIN to TMAX SOURCE CURRENT (VOUT = 2.4 V) TMIN to TMAX THREE-STATE LEAKAGE CURRENT OUTPUT CAPACITANCE DIGITAL INPUT VOLTAGE V INL V INH DIGITAL INPUT CURRENT (0 VIN +5 V) IINL I INH INPUT CAPACITANCE 5 0.8 2.0 2.0 4.5 30 8.0 ± 1/2 1 1 5.5 45 0.015 4.5 30 40 8 10 1/2 1/2
AD670A Typ Max
+85
Min
40
AD670B Typ Max
+85 8 10 1/4 1/2
Min
55
AD670S Typ Max
+125 8 10 1/2 1
Units
°C Bit µs LSB LSB
GUARANTEED NO MISSING CODES ALL GRADES 1.5 2.5 1.0 2.0 1.0 2.0 0.75 1.5 0.5 1.0 0.5 1.0 1.5 2.5 1.0 2.0 1.0 2.0 LSB LSB LSB LSB LSB LSB
0 to +255 128 to +127 0 to +2.55 1.28 to +1.27 0.150 1.50 200 40 VCC 3.5 0.150 V CC 1.50 500 200 12.0 8.0
0 to +255 128 to +127 0 to +2.55 1.28 to +1.27 VCC 3.5 0.150 V CC 1.50 200 40 500 200 12.0 ± 1/2 1 1 5.5 45 0.015 4.75 8.0
0 to +255 128 to +127 0 to +2.55 1.28 to +1.27
mV mV V V
VCC 3.5 V V CC V 200 40 750 200 12.0 ± 1/2 1 1 5.5 45 0.015 nA nA k LSB LSB LSB V mA % of FS/%
30
1.6 0.5 40
1.6 0.5 40 5 0.8
1.6 0.5 40 5 0.7 2.0
mA mA µA pF V V
100 +100 10
100 +100 10
100 + 100 10
µA µA pF
NOTES 1 Tested at VCC = 4.5 V, 5.0 V and 5.5 V for A, B grades; 4.75 V, 5.0 V and 5.5 V for S grade. 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.
REV. A
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AD670
ABSOLUTE MAXIMUM RATINGS*
VCC to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V to +7.5 V Digital Inputs (Pins 1115) . . . . . . . . . . . 0.5 V to VCC +0.5 V Digital Outputs (Pins 19) . Momentary Short to VCC or Ground Analog Inputs (Pins 1619) . . . . . . . . . . . . . . . 30 V to +30 V Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 mW Storage Temperature Range . . . . . . . . . . . . . 65°C to +150°C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . +300°C
*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 them or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Figure 1. AD670 Block Diagram and Terminal Configuration (AII Packages)
ORDERING GUIDE
Model1 AD670JN AD670JP AD670KN AD670KP AD670AD AD670BD AD670SD
Temperature Range 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 40°C to +85°C 40°C to +85°C 55°C to +125°C
Relative Accuracy @ +25 C ± 1/2 LSB ± 1/2 LSB ± 1/4 LSB ± 1/4 LSB ± 1/2 LSB ± 1/4 LSB ± 1/2 LSB
Gain Accuracy @ +25 C ± 1.5 LSB ± 1.5 LSB ± 0.75 LSB ± 0.75 LSB ± 1.5 LSB ± 0.75 LSB ± 1.5 LSB
Package Option2 Plastic DIP (N-20) PLCC (P-20A) Plastic DIP (N-20) PLCC (P-20A) Ceramic DIP (D-20) Ceramic DIP (D-20) Ceramic DIP (D-20)
NOTES 1 For details on grade and package offerings screened in accordance with MIL-STD-883 refer to the Analog Devices Military Products Databook. 2 D = Ceramic DIP; N = Plastic DIP; P = Plastic Leaded Chip Carrier.
CIRCUIT OPERATION/FUNCTIONAL DESCRIPTION
The AD670 is a functionally complete 8-bit signal conditioning A/D converter with microprocessor compatibility. The input section uses an instrumentation amplifier to accomplish the voltage to current conversion. This front end provides a high impedance, low bias current differential amplifier. The common-mode range allows the user to directly interface the device to a variety of transducers. The AID conversions are controlled by R/W, CS, and CE. The R/W line directs the converter to read or start a conversion. A minimum write/start pulse of 300 ns is required on either CE or CS. The STATUS line goes high, indicating that a conversion is in process. The conversion thus begun, the internal 8-bit DAC is sequenced from MSB to LSB using a novel successive approximation technique. In conventional designs, the DAC is stepped through the bits by a clock. This can be thought of as a static design since the speed at which the DAC is sequenced is determined solely by the clock. No clock is used in the AD670. Instead, a "dynamic SAR" is created consisting of a string of inverters with taps along the delay line. Sections of the delay line between taps act as one shots. The pulses are used to set and reset the DAC's bits and strobe the comparator. When strobed, the comparator then 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 turned off. After all bits are tested, the SAR holds an 8-bit code representing the input signal to within 1/2 LSB
accuracy. Ease of implementation and reduced dependence on process related variables make this an attractive approach to a successive approximation design. The SAR provides an end-of-conversion signal to the control logic which then brings the STATUS line low. Data outputs remain in a high impedance state until R/W is brought high with CE and CS low and allows the converter to be read. Bringing CE or CS high during the valid data period ends the read cycle. The output buffers cannot be enabled during a conversion. Any convert start commands will be ignored until the conversion cycle is completed; once a conversion cycle has been started it cannot be stopped or restarted. The AD670 provides the user with a great deal of flexibility by offering two input spans and formats and a choice of output codes. Input format and input range can each be selected. The BPO/UPO pin controls a switch which injects a bipolar offset current of a value equal to the MSB less 1/2 LSB into the summing node of the comparator to offset the DAC output. Two precision 10 to 1 attenuators are included on board to provide input range selection of 0 V to 2.55 V or 0 mV to 255 mV. Additional ranges of 1.28 V to 1.27 V and 128 mV to 127 mV are possible if the BPO/UPO switch is high when the conversion is started. Finally, output coding can be chosen using the FORMAT pin when the conversion is started. In the bipolar mode and with a Logic 1 on FORMAT, the output is in two's complement; with a Logic 0, the output is offset binary. 4 REV. A
AD670
CONNECTING THE AD670
The AD670 has been designed for ease of use. All active components required to perform a complete A/D conversion are on board and are connected internally. In addition, all calibration trims are performed at the factory, assuring specified accuracy without user trims. There are, however, a number of options and connections that should be considered to obtain maximum flexibility from the part.
INPUT CONNECTIONS
Standard connections are shown in the figures that follow. An input range of 0 V to 2.55 V may be configured as shown in Figure 2a. This will provide a one LSB change for each 10 mV of input change. The input range of 0 mV to 255 mV is configured as shown in Figure 2b. In this case, each LSB represents 1 mV of input change. When unipolar input signals are used, Pin 11, BPO/UPO, should be grounded. Pin 11 selects the input format for either unipolar or bipolar signals. Figures 3a and 3b show the input connections for bipolar signals. Pin 11 should be tied to +VCC for bipolar inputs. Although the instrumentation amplifier has a differential input, there must be a return path to ground for the bias currents. If it is not provided, these currents will charge stray capacitances and cause internal circuit nodes to drift uncontrollably causing the digital output to change. Such a return path is provided in Figures 2a and 3a (larger input ranges) since the 1k resistor leg is tied to ground. This is not the case for Figures 2b and 3b (the lower input ranges). When connecting the AD670 inputs to floating sources, such as transformers and ac-coupled sources, there must still be a dc path from each input to common. This can be accomplished by connecting a 10 k resistor from each input to ground.
3a. ± 1.28 V Range
3b. ± 128 mV Range
NOTE: PIN 11, BPO/UPO SHOULD BE HIGH WHEN CONVERSION IS STARTED.
Figure 3. Bipolar Input Connections
Bipolar Operation
Through special design of the instrumentation amplifier, the AD670 accommodates input signal excursions below ground, even though it operates from a single 5 V supply. To the user, this means that true bipolar input signals can be used without the need for any additional external components. Bipolar signals can be applied differentially across both inputs, or one of the inputs can be grounded and a bipolar signal applied to the other.
Common-Mode Performance
2a. 0 V to 2.55 V (10 mV/LSB)
The AD670 is designed to reject dc and ac common-mode voltages. In some applications it is useful to apply a differential input signal VIN in the presence of a dc common-mode voltage VCM. The user must observe the absolute input signal limits listed in the specifications, which represent the maximum voltage VIN + VCM that can be applied to either input without affecting proper operation. Exceeding these limits (within the range of absolute maximum ratings), however, will not cause permanent damage. The excellent common-mode rejection of the AD670 is due to the instrumentation amplifier front end, which maintains the differential signal until it reaches the output of the comparator. In contrast to a standard operational amplifier, the instrumentation amplifier front end provides significantly improved CMRR over a wide frequency range (Figure 4a).
2b. 0 mV to 255 mV (1 mV/LSB)
NOTE: PIN 11, BPO/UPO SHOULD BE LOW WHEN CONVERSION IS STARTED.
Figure 2. Unipolar Input Connections
REV. A
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