I need to measure relative small currents (10 mA to 500 mA) from the high side at mains voltage (230 VAC RMS) levels. I also need a high resolution and preferably high accuracy for the measurement. The method chosen is to use a current shunt resistor and pair it with a current sense amplifier. CSA then converts the differential voltage over the current shunt to single-ended output voltage that I can measure with a microcontroller.
My question is; if I select for example an INA4180 as my CSA measuring the current shunt resistor, am I violating its specs by exposing it to line voltage levels? INA4180 is specified as having maximum common mode voltage of 26 volts but is this just the spec for voltage over the current shunt? I think I'm safe, but can you verify?
Other parts in the circuits are the microcontroller and some sort of isolation barrier over which the MCU communicates measurement values digitally. If all this "mains side" stuff is fed from an isolated DC-DC converter with no connection to mains phase or neutral (or earth), is this a viable scheme? I think the measuring system would then be floating without any galvanic connection to mains and I'm free to measure just the voltage differential generated by the current shunt resistor. I don't have any schematics drawn yet.