how do you estimate the value of the charge pump capacitor ?
416nF10=640nF,
The charge pump capacity need to be large enough to keep the voltage drop low during driving MOSFET input capacity. There are expected 4 MOSFETs to drive, every with 16nF maximum input capacity. Ten times the gate capacity means we will have a voltage from eg. 11V charged C30, drop to 10V in the moment the MOSFETs are switched. You do not want to have C30 too large, because startup will be slowed down then.