A voltage proportional to a sum of currents flowing though first and second coupled inductors is developed across a first capacitor common to first and second series RC networks if the RC networks are time constant-matched to the inductors. The first and second inductors are coupled between a first and second switched drive phase input terminal, respectively, and an apparatus output terminal. The first and second RC networks are coupled in parallel with the first and second inductor, respectively. Inverting and non-inverting inputs of an amplifier are coupled to junctions of third and fourth time constant-matched series RC networks coupled in parallel with the first and second inductors, respectively. The amplifier subtracts voltages sensed at the junctions to generate a difference signal proportional to a magnitude difference of the currents flowing through the inductors.