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UCC21520: UCC21520 negative switching spike

Steven He92
Expert 2125 points
Part Number: UCC21520

Dear Sir,

My customer use UCC21520 and refer datasheet fig-37( Negative Bias with Single Power Supply and Zener Diode in Gate Drive Path)

Please see attached file, page2,3 red block

Question: how to improve LS_GS negative voltage?

Please kindly advise.

Thanks!

Steven

UCC21520.pptx

  • 0
    TI__Guru**** 189401 points
    Hi Steven,

    I don't understand your concern. You aren't seeing the expected negative voltage on the gate?
  • 0 in reply to Don Dapkus
    Expert 2125 points
    Dear Sir,

    Yes! my customer hope can improve negative voltage spike when LS_GS turn-on(red block).
    How to fine tune this application circuit value?
    Thanks!
    Steven
  • 0 in reply to Steven He92
    TI__Mastermind 33690 points

    Hello Steven,

    I am an applications engineer working with high power drivers. I can offer some assistance.

    It looks like the gate-source voltage is spiking negative whenever the switch node transitions from high to low voltage, but it is difficult to tell from the scope shots since the switch node is not captured. I think the dv/dt of the switch node is causing high current to flow from the output of the IC, through the Cz capacitance, and through the parasitic Cgd capacitor. To test this theory, when the switch node dv/dt is reduced, does this improve the problem? Also, when the value of Cz is increased, does this improve the problem? Note that if Cz is increased, Rgs must be decreased to maintain the same time from start of switching to stable negative bias.

    If neither of these suggestions can improve the negative spiking, please let me know and we will continue to look for a solution.

    Regards,