Wide range input current measurement circuit for switching step down DC-DC regulator

Abstract:
Input current measurement circuit intended for switching step down DC-DC regulator is presented in this work. This circuit can be used for effective input current limiting. The method is based on integration of PMOS SenseFET parallel to high side power FET, keeping equal potentials on same terminals of these devices. This way current passing through power FET is accurately mirrored into SenseFET scaled by area ratio of transistors. Current to voltage conversion of the measured result is performed afterwards by the processing circuitry along with the averaging function giving out the final DC voltage, which is proportional to the average input current. The design was performed in 0.35?m technology. The best results can be reached on moderate to high load currents (up to 3A) where +/-5% inaccuracy can be achieved. Keywords - input/output current measurement; buck regulator; SenseFET