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

Question

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

Answer 1

The LM5106 uses the \$Q_g(max)\$ term from the FET datasheet (see section 8.2.1 of the LM5106 datasheet)

From the datasheet for the CSD18531Q5A MOSFET referenced:

As you can see, this is the total (maximum) gate charge.

\$Q_gs(max)\$ is sometimes used as a synonym for \$Q_g(max)\$ (somewhat confusingly)