UCC28180: About FET current for boost

Hello Masazumi Ishii,

There is a parasitic capacitance between the drain and source of the FET and when the FET turns off this Cds need to charge from 0V to the high voltage output of the pfc.
The step change from 0V to 400V causes ringing in the current due the interaction of Cds and L (the boost inductance)
This ringing is most pronounced at high line and light load when the controller goes into a DCM condition
You will not observe this at higher loads.
You can add a small ferrite bead on the drain in order to attenuate this ringing and reduce the EMI that this causes.

Regards

John