Multistep Soft Turn-Off Time Control to Suppress the Overvoltage of SiC MOSFETs in Short-Circuit State

Abstract

Wide-bandgap (WBG) devices, such as silicon carbide (SiC) MOSFETs and gallium nitride (GaN) FETs, have replaced silicon insulated gate bipolar transistors (Si-IGBTs) in recent years, because WBG devices can achieve fast switching frequencies and improved temperature variation reliability with better characteristics. However, this fast-switching operation can cause a substantial drain-source voltage ( $V_{\mathrm {DS}}$ ), which can damage the WBG switch device in the short-circuit state because the gate driver turns off the device extremely quickly, resulting in a substantial $\Delta I / \Delta t$ owing to the large drain current. Therefore, this study presents a multi-step soft turn-off time control method capable of changing the turn-off time according to the $V_{\mathrm {DS}}$ variation using one external capacitor and simple control blocks. The proposed multi-step soft turn-off method suppresses the $V_{\mathrm {DS}}$ variation under the setup voltage regardless of changes in the operating conditions and device characteristics by using a simple structure. An entire control block fabricated using a 180 nm BCDMOS process achieved real-time $V_{\mathrm {DS}}$ sensing with only one external capacitor to control the number of ON/OFF MOSFETs for the 9-level soft turn-off operation and suppressed the $\Delta V_{\mathrm {DS}}$ voltage under 60 V with a 1200V/25A SiC MOSFET power module.

Keywords

• Multi-step off-time control
• overcurrent detection
• SiC MOSFET
• soft switching