This question is not just for thingmaker3 if anyone else has the answers I seek.
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
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