Simplified Gate Driving Strategy for GaN-Based Multi-level Buck Converters Operating at MHz Switching Frequencies

Abstract

The utilization of low voltage rated gallium nitride field-effect transistors (GaN FETs) on flying capacitor multilevel (FCML) converters enabled multi-MHz switching frequency and improved the efficiency for telecommunication and data center applications. However, the gate driving circuit of a multi-level buck converter requires a dedicated DC power supply, a gate driver IC, and a signal isolator IC for each semiconductor device, which reduces the power density and increases the complexity of the high-frequency design. In this paper, a generalized gate driving strategy is proposed for flying capacitor three-level (FCTL) converter, which uses only two half-bridge gate driver ICs to drive the four GaN MOSFETs. A novel cascaded bootstrapping architecture with a single auxiliary DC source was proposed to meet the DC power supply requirements of the half-bridge gate driver ICs. The proposed gate driver uses a minimal number of parts to reduce the complexity and improve the power density to benefit the high switching frequency operation. An experimental prototype is built and tested up to 40 MHz PWM switching frequency. Results are presented as proof of concept.