My application is roughly depicted in the attached image.
I am sensing a Vin voltage, by dividing down with a resistive divider, then passing the signal through an opamp and an RC filter (not shown) and lastly convert with an ADC.
My concern is: what happens if the board's supply (+5V and +3.3V) is removed but Vin remains? Is that potentially harmful for the opamp / ADC?
If yes, is there a standard way to protect them against such a case?
I thought of intercepting Vin right before the divider with a MOSFET switch, but then I will probably not be able to sense very low voltages, since Vin should be larger than Vth of the MOSFET in order for the switch to be on.