High Side Current Sensing for Low Side Switching

An AD8205 can be used to make a high-side current sense with a low side switch. Besides AD8205, an inductive load (solenoid) and a resistive shunt are added in this circuit. The resistive shunt is placed on high-side and the switch is placed on low-side, so that all current measurements, including the the re-circulation current, can be done because when the switch is off, the shunt still in loop. Besides that, placing the shunt on high side, shorts to ground can be detected, so diagnostics can be optimized. Here is the schematic diagram of the circuit:

When we connect the switch, the common-mode voltage will move down to near the negative rail. If we disconnect the switch, the common-mode voltage drop above the battery because of the voltage reversal that across inductive load. [Circuit’s schematic diagram source: Analog Application Note]