I'm trying to determine a MOSFET for a circuit I'm building which will drive the gate of an N-channel MOSFET at 3.3v with an available current 40mA (**this will be driven using PWM at 4MHz), the MOSFET will be driving a load of 10A at 3.5v. I'm not sure what characteristic I should be looking at to create the most efficient circuit. I know that I'll need a low RDSon but I'm not sure if gate capacitance or anything else comes into play when choosing a MOSFET.
Appreciate any help!
Assume the gate capacitance is 1 nF. For a 4 MHz operating frequency the period is 250 ns so, you might want switching time in one period to be 10% of this (or less) to give decent efficiency. That means 12.5 ns for charging up that gate capacitance or discharging it (maximum).
I = C dv/dt hence I = 264 mA just to charge the gate.
I took dv at 3.3 volts and dt as 12.5 ns.
Given that you have 40 mA available you'll need a driver because I really don't think you'll find a MOSFET that can handle 10A and have a gate capacitance of 100 pF.
