I've gotten interested in using GaN FETs for their combination of fast switching speed and very low on-state resistance. Most of the eval boards (for example by EPC) use GaN driver chips such as UCC27611 and LM5113 which regulate the gate voltage to 5V and clamp transients.
Now, looking at some of the smaller GaN FETs like EPC2037 which has 0.12nC gate charge or EPC2036 with 0.70nC, I'm wondering: is there any reason this cannot be driven directly from a 3.3V microcontroller pin?
If the microcontroller can source/sink 25mA, the switching time is in theory only 0.12nC/25 mA = 4.8ns, and that's without a driver (!!). The real switching time may not be quite as good of course, but it should still be super-fast compared to a non-GaN FET. I would like to tie the gate to a microcontroller pin without a gate resistor, if possible.
Now, I can see from the same datasheet that FET won't be fully on at 3.3V, but does this have any negative effect other than slightly higher heat dissipation? I'm okay with lower efficiency, just want to know if there are any pitfalls of the kind that could make the FET fail.
(My use scenario is switching 5V 1A at ~1MHz, I think 20-50ns switching times should be fine but faster is better. The microcontroller is STM32F103)