Power supply of isolation amplifers

Question

First time experimenting with a design with isolation amplifiers and I am unsure about the amplifier power supply range I need.

I need to provide isolation to measure a current between 0 and 7.4mA. Plan is to use a shunt on the hot side and pass the voltage drop to an isolation amplifier such as AMC1200 or ISO124.

I know op-amps do not work well when the signal is close to one of the rails. Is that the same for these isolation amplifiers? Does it mean I need a negative power supply on the hot side or a divider resistor on my signal to move it away from zero when I need to measure a zero current?

Answer 1

The AMC1200 works best when VINN is at or near GND. It even shows this in basically all examples TI has published. It's common mode range is limited, but it is able to do -0.16V to VDD1, which means you're allowed to pin it to GND.

It has a differential input, so the 1.5mV input offset are valid between VINN and VINP.

Since you're using isolation amplifier you could also lift the entire circuit. Like this. But better impedance may be required.

^{simulate this circuit – Schematic created using CircuitLab}

But you don't need to, and this may introduce additional error.