matching drivers to MOSFETs
I found
this application Note which is finally shedding some light on how to select the right driver for
my MOSFET.
My Mosfet has a Ciss of 6540pF and I want to run PWM @ 20KHz.
I want to drive 6 of them in parallel, and still not sure if I will need 6 drivers or only one.
Anyway, the Application note has a nice chart for selecting one of their Drivers for a given Ciss, but I was thinking of going with
a driver of a different brand, which has a max output of 11.4A.
The application note says at the bottom:
Quote:
To match any MOSFET to its proper driver, use the chart above
(which will take care of the largest number of applications), or use
the simple formula: rise time (dt) = driver supply voltage (dV),
times capacitance (C), all divided by driver peak current (I);
restated:
dt = [(dV)xC]/I
I assume that dV in this formula is Vdd in the driver?
So, using the max (for the FAN3121 driver) of 18V, that would be my dv?
dt = (18V * .000,000,006,540)/11.4 = 10.3nS?
seems awefully low. too good to be true? I'm not sure I'm doing this right... plus I need to add a gate resistor. Lets say I add a 10Ω resistor (do I really need to go all the way to 10Ω?), which is going to limit current to 1.8A
then
(18V * .000,000,006,540)/1.8A = 1.1772μS?
That made a big difference. Not sure what size gate resistor to use. the application note shows in figure 4 2.2-22Ω; I would assume you would want to go with the smallest possible, but not sure.
Also I know I read somewhere that frequency plays a part in this, but the equation did not include frequency. AAAHH I don't know what's going on! (pulling my hair out)
Should I just go with the TC4422 that the application note suggests (10,000pF)?