A Dynamic Two-Stage Gate Driver for Unlocking the Fast-Switching Potential of GaN HEMT

The gate terminal of mainstream Schottky-type p-GaN gate high-electron-mobility transistor (HEMT) is particularly vulnerable to the gate voltage ringing during the fast-switching transient due to its narrow gate voltage headroom for safe operation. In this work, a new gate driver circuit with expanded gate voltage headroom and suppressed gate-loop oscillation/ringing is proposed. The new design is based on a dynamic two-stage turn-on process enabled by a GaN lateral field-effect rectifier (L-FER)-resistor pair that can self-adaptively adjust the gate charging speed according to the real-time gate voltage, enabling fast charging during the initial turn-on stage and slow charging when the gate is near complete turn on. The latter stage effectively suppresses the gate-loop oscillation to enable an elevated gate turn-on voltage for a stronger yet safe gate overdrive to suppress the dynamic RON degradation in the GaN HEMT. Such a dynamic two-stage gate voltage profile can be realized without additional active sensing or control. The GaN L-FER is implemented with a low-voltage GaN HEMT in the diode mode that is free of reverse recovery issues. Equipped with this dynamic two-stage gate driver, the fast-switching potential of the GaN HEMT can be fully unlocked to reduce the switching loss without gate overstress; meanwhile, the switching oscillation can also be suppressed significantly.