**Part Number:**UCC28910

Hello,

I have some doubts on VDD capacitor sizing. At startup, the controller is off, so CVDD is charged with the High Voltage current source until VDDon is reached.

From that moment on device starts switching and regulation is achieved.

Increasing the capacitor value will lead to longer startup times.

The suggested value for CVDD is given by the following equation, according to the device data sheet:

May anyone comment this equation and give more details?

What if I have another device at the primary side that draws current (3 mA) from the rectified auxiliary? May I consider that contribution on top of IRUN_max?

Thanks.