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UCC28781: About adaptive ZVS control

Ryoma Ohashi
Expert 5555 points
Part Number: UCC28781


Tool/software:

Hi team,

I have a question about adaptive ZVS control.

If Vsw doesn't reach Vth(sws) within tz, the IC will make the tdm longer to make the negative Im bigger, right?

What if Vsw reachs too fast to Vth(sws)? Will the tdm optimizer make the tdm shorter?

Will IC compare the time to reach to Vth(sws) with tz every cycle? And make the tdm shorter is it is shorter compared to tz?

Regards
Ohashi

  • 0
    TI__Genius 12795 points

    Ohashi,

    Please give us few days to get back to you.

    Thanks

  • +1 in reply to Ning Tan
    TI__Mastermind 40580 points

    Hello Ohashi-san, 

    The answer to each of your questions is Yes. 

    But proper operation of the tDM and Dead-Time Optimizers depends on having the zero-voltage crossing at the VS input precede the Vsw crossing of the Vth(sws) threshold.  
    If the VS signal is delayed by excess capacitance so that Vsw crosses Vth(sws) before VS voltage falls < 0V, then the tDM may be driven excessively long and generate too much negative Im current.  This reduces efficiency due to excess -Im. 

    Please make sure that the VS and SWS input signals follow the correct timing sequence to their respective thresholds. 

    Regards,
    Ulrich