Non-destructive current measurement for surface mounted power MOSFET on VRM board using magnetic field probing technique

This paper proposes nondestructive current measurement for surface mounted power MOSFET on VRM board using the micro-magnetic probing technique to facilitation discussion of the self-turn-on phenomenon. A notable feature of the proposed technique is that the sensor part is much smaller than that of conventional methods because this method measures the intensity of a partial magnetic field caused by wire bonding inductance, whereas the conventional method employs a loop coil structure around the current flow. The small sense part enables measurement of the VRM board itself 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 successfully detect shoot through current waveform for 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 VRM board transient current and indicates the importance of board GND layout distribution behavior in determining highly accurate trade-off between switching loss and self-turn-on loss.