Analysis of Switching Noise Mechanism and Proposal of Improvement Measures Focused on Capacitance-Voltage Characteristics of Superjunction-MOSFET

Abstract

The switching noise mechanism of a high voltage superjunction-MOSFET loaded into a power supply is analyzed. The device model is developed using BSIM3 MOSFET model with voltage-dependent capacitors. Inductive load switching with test-circuit parasitic elements is simulated, and the switching surge generated during turn-off transient is discussed. A sharp drop of drain-source capacitance (C_ds at the turn-off transient causes high voltage ringing, whose frequency is determined using total capacitances and stray inductances in the power loop circuit. The optimization of C_ds-voltage characteristic and additional C_gs with small capacitance are proposed as an effective method for suppressing surge generation. The voltage ringing level is improved by slightly modifying the C_ds-voltage curve and additional C_gs. In addition, test results show that the radiated EMI decreased.