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

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.