UCC20225-Q1: Channel B’s capacitance CVDD calculation formula and method

Hi Alan,

The VDDB capacitor should:

• Provide the gate charge with limited voltage drop
• Provide the quiescent current to the driver
• Should provide the charge to the bootstrap cap if used

With this in mind, the equation to size the VDDB capacitor is:

with the total charge in B being:

The smaller ~0.22uF capacitor is recommended to be placed in parallel to filter out higher frequency noise which may be induced by long PCB traces. The capacitance value actually is not that significant for the high frequency capacitor. The biggest effect is the capacitor size, which for this capacitor, should be as small as possible. 

Regards,

Hiroki

Hi Alan,

This should be the total gate charge, Qg.

Regards,

Hiroki

It should be the total gate charge of the MOSFET load of channel B. Which in the datasheet would be 32nC for max specification case.