Cboot > (Qg + Dmax*Tsw*Idrv ) / ΔV

Where:

Qg is the gate charge of the MOSFET

Dmax is the maximum duty-cycleTsw is the switching periodIdrv is the average consumption of the driverΔV is the ripple you accept across the bootstrap capacitor

So I tried the calculation its much more simple then the one I was going to use from the application guide, but I'm getting a fairly large value.

So lets do one.

Cboot must be larger than: (Qg + Dmax*Tsw*Idrv ) / ΔV

(.00000017 + .75*20000*.2) / 2

is equal to 1500.000000085. This would appear to be 1500 farads?

What am I doing wrong?

Or, if I don't convert to actual values I could do:

(170nC + 75% * 20khz * 200mA) / 2v

and get a value of 235 which I could assume means 235 picofarads?

So a tally of the issues I'm having:

1) Did I do any of the calculations right?

2) Do I use the average current of my driver or peak pulse current?

3) What happens when you get to duty cycles of 1% and 99%?

4) A 2V ripple? Meaning I'm driving with 12v and will allow it to sag to 10v.

Thanks

TriX