Help in HIP4081A bootstrap circuit

[dileepkella85]

Hello, anybody have worked on HIP4081A MOSFET driver IC.............

I went through Application note of HIP4081A.

I could not understand the bootstrap capacitor calculation,
the formula is given as

CBS= {Qg + Qrr + (IDR +IQBS)/fPWM}/(VBS1-VBS2)

during the calculation it is said that the value of IDR and IQBS is negligible so the simplified formula becomes as

CBS = (QG + Qrr) / (VBS1-VBS2)
where,
Qg= Turn on gate charge transferred (Which can be taken from MOSFET datasheet)
Qrr= Bootstrap diode reverse recovery charge (which can be take from diode spec sheet)

VBS1= bootstrap capacitor voltage just after refresh
VBS2= bootstrap capacitor voltage just after upper turn on

I dont how what value should I take for VBS1 and VBS2

The example which is given there, has taken (12.0 - 11.0)
I dont know how........

you can have a look at the file by this link http://www.intersil.com/data/an/an9405.pdf

at eq:3 on page 6 and eq:4 on page 7.

if you could explain.....

Thank you.
Regards,
Dileep

[luka]

Well that is basic calculation, for min capacitor size needed.. you can always just use 10u-100u and don't calculate anything

[dileepkella85]

Ok, thank you luka.