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UCC28780: the driver issue of UCC28780

Part Number: UCC28780

Hi the expert,

I have a problem when I use UCC28780 with GaN devices in 65W charger demo,  under light load , the driver has two pulses, but the first pulse is too short, which is only about 130ns, Could you help me to explain the reason and tell me some way to solve the problem? 

  • Hi Quanchun,

    Thanks for your interesting in TI's part.

    the 130ns is lead edge blanking time, that means voltage spike on CS pin of UCC28780 is still higher than internal threshold after blanking time. the first pulse is hard switch at a higher voltage . while there is a interwinding capacitor on transformer need to be charged , and bootstrap capacitor need to be charged . so current spike is high . solution are :1. Increase CS pin filter time constant , Ccs increase to such as 100pF ~220pF , Ropp change to such as 1.5k.

    2. Decrease the turn on slew rate of low side GaN mosfet .

    3. Increase the in series resistor on bootstrap path , I am not sure if you already have this resistor and what the value , change to such as 4.7ohm.

    That is will help you to solve this problem