EVAL-CN0179-PMDZ: 4-20 mA Low Power, 14-Bit, Process Control Current Loop Transmitter

The circuit on EVAL-CN0179-PMDZ is a 4 mA-to-20 mA current loop transmitter for communication between a process control system and its actuator. The circuit output is 0 mA to 20 mA of current, and it operates on a single supply from 8 V to 18 V. The 4 mA to 20 mA range is usually mapped to represent the input control range from the DAC or micro-controller, while the output current range of 0 mA to 4 mA is often used to diagnose fault conditions.

The 14-bit, 5 V AD5641 requires 75 µA typical supply current. The AD8657 is a rail-to-rail input/output dual op amp and is a low power amplifier (22 µA per amplifier over the full supply voltage and input common-mode range) with high operating voltage of up to 18 V. The ADR02 ultracompact precision 5 V voltage reference requires only 650 µA. Together, these three devices consume a typical supply current of 747 µA.

The circuit has a 12-pin Pmod™ digital interface (Digilent specification).