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:
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)?
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:
I assume that dV in this formula is Vdd in the driver?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
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)?