A continuous output current measurement circuit for switching step down DCDC regulator with a single sensing FET

An output current measurement circuit intended for using with a switching type step down DC-DC voltage regulator is presented in this work. The approach is based on utilizing only high side sensing device, but unlike other similar solutions, the results are obtained continuously, i.e. the information of full load current is delivered without any periodic notches or undershoots of the measured signal in time domain. The method is implemented by integration of the PMOS SenseFET parallel to the high side power FET with keeping equal potentials on same terminals of the transistors. This way current passing through power FET is accurately mirrored into SenseFET scaled by area ratio of the transistors. The lossless operation is obtained by inclusion of a sample and hold circuit at the output with the further averaging of the result by a low pass filter.