A GaN-Based Gate Driver with Adaptive Charge Sharing Bootstrap Technique to Improve the Conduction Loss

This work presents a half-bridge gallium nitride (GaN) buck converter using an adaptive charge sharing bootstrap (ACSB) technique to stabilize the bootstrap capacitor voltage. The conventional bootstrap technique relies on preset calculation to decide the bootstrap capacitance. However, the PCB parasitic capacitance and Q_g variations compromise the results. Moreover, the fixed bootstrap capacitance limits the practicality in monolithic gate drivers and only few GaN transistors with certain gate charge (Q_g) range can be used. The proposed ACSB improves the conduction loss and avoids the gate overstress in GaN devices. In addition, the charge sharing technique requires merely a small on-chip bootstrap capacitor, which eliminates the bulk volume of the off-chip capacitor. The prototype is simulated in TSMC T18HVG2 process. Simulation results show that when Q_g ranges from 115 pC to 585 pC, the bootstrap voltage steadily maintains at 4.7 V. The overshoot and undershoot are 16.2 mV and 19.6 mV, respectively when the load current transits between 2A and 500 mA. The peak power efficiency of 93.2 % is obtained.