A load is powered between positive and negative rails. A switching converter generates the negative rail voltage based on an input voltage, with a power transistor involved therein. A replica generator produces a replica voltage mirroring the drain-to-source voltage of the power transistor. A buffer buffers the replica voltage. A first switch selectively connects the buffered voltage to an output node, in response to a control signal with a duty-cycle proportional to the input voltage divided by the negative rail voltage. A second switch selectively connects the buffered voltage to ground, according to the inverse of the control signal, resulting in a PWM signal at the output node. An output filter filters the PWM signal to generate a sense voltage indicative of the output current flowing from the load device. A processing circuit determines the input current from the positive rail to the load device based on the sense voltage.