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UCC27201 repeating restart

Other Parts Discussed in Thread: UCC27201

Hi

Our customer are evaluating UCC27201 in secondry side of isolated application such as full bridge converter.

There is a abnormal phenomenon on customer's board. Please see following waveform.

It is repeating restart because the voltage of VDD is below UVLO during it is starting.

Condition : Vin=48V,Io=0A,Vo=12V    VDD-VSS:1uF, HB-HS:0.1uF

How much capacitor does it need?  It looks the input current is large.

 

Regards,

Koji Hamamoto