Hi Allen,
The di/dt is a lot faster with GaN. In my last projected, I saw a 3 ns turn off time. A newer faster generation 40 A IGBT at 90 C is more than 10 times slower at turn off. If you consider high currents and PCB inductance, you’re going to get a lot of V from V=Ldi/dt. You may need more capacitance to absorb that energy or improve your PCB layout to reduce your inductance. The best way to achieve a “best design” is to start your PCB layout with high frequency GaN in mind. The common mistake is to keep 99% of the PCB layout the same as it was for the IGBT layout, and simply change the footprint to drop in GaN device.
Regards,
Perry Rothenbaum