LTC1453/LT1077/LT1121 Isolated 4 – 20mA Current Loop

This circuit is a computer-controlled 4 – 20mA current loop. It is designed to operate on a single supply over a range of 3.3V to 30V. The circuit’s zero output reference signal, 4mA, is set by R1 and calibrated using R2, and its full-scale output current is set by R3 and calibrated using R4. The zero and full-scale output currents are set as follows: with a zero input code applied to the LTC1453, the output current, IOUT, is set to 4mA by adjusting R2; next, with a full-scale code applied to the DAC the full-scale output current is set to 20mA by adjusting R4.