High side current sensing should be used when low side current sensing is not an option due to the added resistance to ground. When using high side current sensing, the resistive current sensor is placed between the supply and load. The current sensor can then detect any downstream failure. This, however, requires very accurate resistor matching to have a very high common mode rejection ratio, or CMRR. This is necessary because of the high common-mode voltage between the inputs and ground of the current sensing device, a natural result of measuring current on the high side.