AD694 (Rev.C)
Document overview
- Manufacturer or author: Analog Devices, Inc.
- PDF pages: 19
Technical content
4–20 mA Transmitter Rev. C DOCUMENT FEEDBACK TECHNICAL SUPPORT Information furnished by Analog Devices is believed to be accurate and reliable "as is". However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
FEATURES
►4–20 mA, 0–20 mA output ranges ►Precalibrated input ranges: ►0 V to 2 V, 0 V to 10 V ►Precision voltage reference ►Programmable to 2.000 V or 10.000 V ►Single or dual supply operation ►Wide power supply range: 4.5 V to 36 V ►Wide output compliance ►Input buffer amplifier ►Open-loop alarm ►Optional external pass transistor to reduce self-heating errors ►0.002% typ nonlinearity GENERAL DESCRIPTION The AD694 is a monolithic current transmitter that accepts high level signal inputs to drive a standard 4–20 mA current loop for the control of valves, actuators, and other devices commonly used in process control. The input signal is buffered by an input amplifier that can be used to scale the input signal or buffer the output from a current mode DAC. Precalibrated input spans of 0 V to 2 V and 0 V to 10 V are selected by simple pin strapping; other spans may be programmed with external resistors. The output stage compliance extends to within 2 V of VS and its special design allows the output voltage to extend below common in dual supply operation. An alarm warns of an open 4–20 mA loop or noncompliance of the output stage. Active laser trimming of the AD694’s thin film resistors results in high levels of accuracy without the need for additional adjustments and calibration. An external pass transistor may be used with the AD694 to off-load power dissipation, extending the temperature range of operation. The AD694 is the ideal building block for systems requiring noise immune 4–20 mA signal transmission to operate valves, actuators, and other control devices, as well as for the transmission of process parameters such as pressure, temperature, or flow. It is recommended as a replacement for discrete designs in a variety of applications in industrial process control, factory automation, and system monitoring. The AD694 is available in hermetically sealed, 16-pin CERDIP and plastic SOIC, specified over the –40°C to +85°C industrial temperature range, and in a 16-pin plastic DIP, specified over the 0°C to +70°C temperature range. FUNCTIONAL BLOCK DIAGRAM Figure 1. Functional Block Diagram
- The AD694 is a complete voltage in to 4–20 mA out current
- Pin programmable input ranges are precalibrated at 0 V to 2 V
- The input amplifier may be configured to buffer and scale the
- The output voltage compliance extends to within 2 V of the
- The AD694 interfaces directly to 8-, 10-, and 12-bit single
supply CMOS and bipolar DACs.
- The 4 mA zero current may be switched on and off with a TTL
control pin, allowing 0–20 mA operation.
- An open collector alarm warns of loop failure due to open wires
or noncompliance of the output stage.
- A monitored output is provided to drive an external pass tran-
temperature range of operation and minimize self-heating error.
analog.com Rev. C | 2 of 19 Basic Connections: 12.5 V Single-Supply
REVISION HISTORY
6/2024—Rev. B to Rev. C
analog.com Rev. C | 3 of 19 At +25°C, RL = 250 Ω, and VS = +24 V, unless otherwise noted. All min and max specifications are guaranteed, unless otherwise noted. Table 1. Model AD694JN/AQ/AR AD694BQ/BR UnitMin Typ Max Min Typ Max INPUT CHARACTERISTICS Input Bias Current Either Input, TMIN to TMAX 1.5 51 1.5 51 nA Offset Current, TMIN to TMAX ± 0.1 ±11 ± 0.1 ±11 nA Offset Current Drift ± 1.0 ± 5.0 ± 1.0 ± 5.0 pA/°C Input Impedance 5 5 MΩ OUTPUT CHARACTERISTICS Operating Current Range 0 23 0 23 mA Specified Performance 4 20 4 20 mA Output Voltage Compliance VS –36 V1 VS –2 V1 VS –36 V1 VS –2 V1 V Output Impedance, 4–20 mA 40.0 50.0 40.0 50.0 MΩ Current Limit (@ 2 × FS Overdrive) 241 441 241 441 mA Slew Rate 1.3 1.3 mA/µs SPAN AND ZERO ACCURACY2 4 mA Offset Error @ 0 V Input3 Error from 4.000 mA, 4 mA On ± 10 ±201 ± 5 ±101 µA Error from 0.000 mA, 4 mA Off 0 ± 10 +201 0 +5 +101 µA TMIN to TMAX ± 10 ±401 ± 5 ±201 µA Trim Range, 4 mA Zero 2.0 4.8 2.0 4.8 mA Span Nominal Transfer Function Input FS = 2 V 8.0 8.0 mA/V Input FS = 10 V 1.6 1.6 mA/V Transfer Function Error from Nom, Input FS = 2 V, 10 V± 0.1 ±0.31 ± 0.05 ±0.2251 % of Span TMIN to TMAX ± 0.002 ± 0.005 ± 0.001 ±0.0031 % of Span/°C Nonlinearity4 ± 0.005 ±0.0151 ± 0.001 ±0.0051 % of Span 4 mA On: Max Pin 9 Voltage 0.8 0.8 V 4 mA Off: Min Pin 9 Voltage 3.0 2.5 3.0 2.5 V VOLTAGE REFERENCE TMIN to TMAX5 501 451 ppm/°C Output Current Source 51 5 mA Sink 0.2 0.2 mA ALARM CHARACTERISTICS VCE(SAT) @ 2.5 mA 0.35 0.35 V Leakage Current ±11 ±11 µA Alarm Pin Current (Pin 10) 20 20 mA
Table 1. (Continued) 1 Tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. zero accuracy are tested with the buffer amplifier configured as a follower. 3 Offset at 4 mA out and 0 mA out are extrapolated to 0.000 V input from measurements made at 5 mV and at full scale. See Note 2. 4 Nonlinearity is specified as the maximum deviation of the output, as a % of span, from a straight line drawn through the endpoints of the transfer function. temperature range and whose height is determined by the maximum temperature coefficient multiplied by the temperature span in degrees C. junction and case temperature should not be exceeded. See the Power Dissipation Considerations section. 7 Buffer amplifier specs for reference. Buffer amplifier offset and drift already included in Span and Zero accuracy specs above.
analog.com Rev. C | 5 of 19 No pin, other than IOUT (11) and ±Sig (2), (3) as noted, may be permitted to become more negative than Com (5). No pin may be permitted to become more positive than VS (13). Table 2. Parameter Rating Supply Voltage 36 V VS to IOUT 36 V Input Voltage, (Either Input Pin 2 or 3) –0.3 V to +36 V Reference Short Circuit to Common Indefinite Alarm Voltage, Pin 10 36 V 4 mA Adj, Pin 6 1 V 4 mA On/Off, Pin 9 0 V to 36 V Storage Temperature Range AD694Q –65°C to +150°C AD694N, R –65°C to +125°C Lead Temperature, 10 sec Soldering 300°C Maximum Junction Temperature 150°C Maximum Case Temperature Plastic Package (N, R) 125°C Cerdip Package (Q) 125°C Transistor Count 75 Active Devices Substrate Connection to Com, Pin 5 Thermal Characteristics Plastic (N) Package θJC 50°C/Watt θCA (Still Air) 85°C/Watt Cerdip (Q) Package θJC 30°C/Watt θCA (Still Air) 70°C/Watt Plastic (R) Package θJC 27°C/Watt θCA (Still Air) 73°C/Watt Stresses at or above those listed under Absolute Maximum Ratings may cause permanent damage to the product. This is a stress rating only; functional operation of the product at these or any other conditions above those indicated in the operational section of this specification is not implied. Operation beyond the maximum operat- ing conditions for extended periods may affect product reliability. ELECTROSTATIC DISCHARGE (ESD) SUSCEPTIBILITY All pins are rated for a minimum of 4000 V protection, except for Pins 2, 3 and 9 which are rated to survive a minimum of 1500 V. ESD testing conforms to Human Body Model. Always practice ESD prevention. ESD CAUTION ESD (electrostatic discharge) sensitive device. Charged devi- ces and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.
Figure 2. Pin Configuration Table 3. Pin Function Descriptions can sink only as much as its internal 10 kΩ pulldown resistor allows. connecting FB (Pin 1) to this pin. 3 +SIG Positive Signal (+SIG). This pin is the positive input of the buffer amplifier. 4 2V FS 2 V Full-Scale (FS). The 2 V full-scale option is selected by shorting this pin to Pin 5. 5 COM Common (COM). This pin must be connected to the ground. 6 4mA ADJUST (Adj) 4 mA Adjust (Adj). This pin allows the offset current to be adjusted to any current in the range of 2 mA to 4.8 mA. supply voltages greater than 12.5 V. used with all supply voltages greater than 4.5 V. Float this pin for 10 V voltage reference. 9 4mA ON/OFF Jiggle Pin. This pin can shut off the offset current completely if it is lifted to 3.0 V or more, allowing 0 mA to 20 mA operation. – 2 V. The alarm transistor pulls down if an out of control current is sensed at IOUT. common (substrate) potential of the device. 12 BOOST Boost. A boost transistor can be added to increase the current drive capability of the 2 V mode. 13 VS Positive Supply Voltage (VS). connecting an external capacitor from this pin to Pin 13. 15, 16 VOS ADJUST Input Voltage Offset Adjust (VOS ADJUST).
responsible for providing the 4 mA offset current signal. internal 10 kΩ pulldown resistor allows. dissipation off-chip, to extend the temperature range of operation. voltage greater than VS – 2 V.
4 MA OFFSET GENERATOR
increase the current drive capability of the 2 V mode. configurations, as well as adjustment methods. Table 4 shows possible connection options. Table 4. Precalibrated Ranges for the AD694 load with a 12.5 V supply is 525 Ω.
any parasitic resistance will affect the precalibrated span accuracy. can be used with all supply voltages greater than 4.5 V. increases by approximately 0.7 V. Figure 7. Minimal Connections for 0 V to 10 V Single-Ended Input, 4–20 mA Output, 10 V Reference Output
4.5 V SINGLE SUPPLY OPERATION
output of 2 V as described above. must be added to the inputs if there is a danger of this occurring. (FB) directly; always use the buffer amplifier to buffer input signals. The AD694 is designed to be stable when driving resistive loads. when there is any uncertainty as to the characteristics of the load. Figure 8. Capacitor Utilized When Driving Nonresistive Loads; Protection Additional protection is recommended when driving inductive loads. valves or actuators, or as a way to shut off a 4–20 mA loop entirely. extend lower than –0.3 V of common. compliance of the output stage.
Figure 17. Using the Alarm to Drive a TTL Gate
4 mA offset. Care should be taken in managing the circuit grounds. the load to be driven, and on power dissipation considerations. buffer amplifier serves to buffer the voltage output from the DAC. to full scale would result in an output current of 3.2 mA to 20.8 mA. Figure 18. Digital to 4–20 mA Interface Using a Current Steering DAC
Figure 19. Single-Supply Digital Input to 4–20 mA Output
easily handles these types of low level signals. amplifier is used for the subtractor circuit, as shown in Figure 20. Figure 20. Low Cost Sensor Transmitter
©1996-2024 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. One Analog Way, Wilmington, MA 01887-2356, U.S.A. Rev. C | 19 of 19 Package Drawing (Option) Package Type Package Description Q-16 CERDIP 16-Lead Ceramic DIP-Glass Hermetic Seal Package N-16 PDIP 16-Lead Plastic Dual-in-Line Package RW-16 SOIC 16-Lead Standard Small Outline Package For the latest package outline information and land patterns (footprints), go to Package Index. Updated: April 29, 2024 ORDERING GUIDE Model1 Temperature Range Package Description Packing Quantity Package Option AD694AQ -40°C to +85°C 16-Lead CerDIP TUBE, 25 Q-16 AD694ARZ -40°C to +85°C 16-Lead SOIC Wide TUBE, 47 RW-16 AD694BQ -40°C to +85°C 16-Lead CerDIP TUBE, 25 Q-16 AD694BRZ -40°C to +85°C 16-Lead SOIC Wide TUBE, 47 RW-16 AD694JNZ 0°C to +70°C 16-Lead PDIP TUBE, 25 N-16 AD694ARZ-REEL -40°C to +85°C 16-Lead SOIC Wide REEL, 1000 RW-16 AD694BRZ-REEL -40°C to +85°C 16-Lead SOIC Wide REEL, 1000 RW-16 AD694BRZ-REEL7 -40°C to +85°C 16-Lead SOIC Wide REEL, 400 RW-16 1 Z = RoHS Compliant Part.