# Boost capacitor sizing, gate driver LM5106 used with N-MOSFET IPP075N15N3 G

I am using a TI gate driver LM5106 and I wanted to size the bootstrap capacitor. The application regards a synchronous boost converter. According to pag. 13 I need the $Qgs$ charge of the MOSFET that I am trying to switch. I am using the MOSFET IPP075N15N3G.

What IPP075N15N3G datasheet value should I use to size the boot capacitor needed for the gate driver? I am unsure if I should use the gate charge $Qgs(max)=40nC$ or the gate charge total $Qg(max)=93nC$, reported in page 3 and why.

Thank you so much,

Lello

The LM5106 uses the $Q_g(max)$ term from the FET datasheet (see section 8.2.1 of the LM5106 datasheet)
$Q_gs(max)$ is sometimes used as a synonym for $Q_g(max)$ (somewhat confusingly)