The transmitter has only two external input pins; a supply connection and a ground (or return) connection. The transmitter communicates back to the host, typically a PLC analog input module, by precisely controlling the magnitude of the return current. To conform to the 4-mA to 20-mA communication standards, the complete transmitter must consume less than 4 mA of current.

The complete design of this circuit is outlined in TIPD158, Low Cost Loop-Powered 4-20mA Transmitter EMC/EMI Tested Reference Design. The design is expected to be low-cost and deliver immunity to the IEC61000-4 suite of tests with minimum impact on the accuracy of the system. Reference design TIPD158 includes the design goals, simulated results, and measured performance.