Non-Destructive Current Measurement for Surface Mounted Power MOSFET on VRM Board Using Magnetic Field Probing Technique

Abstract

This paper proposes a nondestructive current measurement using the micro-magnetic probing technique for the surface mounted power MOSFET on VRM board to discuss the self-turn-on phenomenon. Whereas the conventional method employs a loop coil structure around the current flow, a notable feature of the proposed technique is the sensor part which is much smaller than that of conventional methods. This method designed to measure the intensity of a partial magnetic field, therefore enables the non-destructive measurement just by setting the magnetic probe on the MOSFET package. A calibration technique is introduced to reproduce current waveform and we confirm that the obtained current waveform agrees with that obtained by the conventional Current Transformer. Using the proposed technique, we succeed of detecting a shoot through current waveform of high-side power MOSFET during self-turn-on phenomenon in VRM board. We also sense non-uniform current flow among 3 parallel low-side power MOSFETs caused by board layout location. This study demonstrates the capability of sensing local transient current of VRM board.