Normally-off GaN-on-Si multi-chip module boost converter with 96% efficiency and low gate and drain overshoot

A high efficiency synchronous GaN half-bridge boost converter with fast switching and low overshoot is achieved by minimizing parasitic inductance and critical damping the gate drive. A normally-off GaN-on-Si 2.4kW synchronous halfbridge Multi-Chip Module (MCM) is designed with a power-loop inductance of ~4nH using transmission-line techniques to minimize inductance. The gate circuit inductance is reduced to 1nH using bare MOSFET die for driving the GaN gates and a 0.5mil flexible substrate gate transmission-line. Configured as a boost converter with no added gate resistance, the synchronous half-bridge switches 400V in only 1.3ns. The high voltage slew rates of 325V/ns results in overshoot of 200V on the drain and 4V overshoot on the gate, both of which may damage the GaN switches. Critically damping the gate turn-on reduces overshoot to safe levels of 1V gate overshoot and ~20V drain overshoot. The gate damping increases drain fall time to 3ns, which only decreases efficiency by 0.2% at 1MHz. The resulting synchronous boost converter has an efficiency of 96%, switching 300V at 1MHz with 50% duty cycle and an output power of 2.4kW. The high efficiency of GaN switches and the 0.6C/W thermal resistance of the MCM enable a maximum junction temperature of 65°C.