AD694 4-20mA Transmitter

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. Pre-calibrated 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.

Features of AD694

• 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