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UCC28782:I have a question about the function of UCC28782CD

maki.masashi
Prodigy 20 points
Part Number: UCC28782 
I have a question about the function of UCC28782CD

What determines the reset voltage for tFDR restart (1.5 seconds)?
If VDD(RST) falls below 4.3V, will the tFDR restart (1.5 seconds) be canceled?
  • 0
    TI__Mastermind 26840 points

    Hello Masashi-san, 

    Thank you for your interest in the UCC28782CD active-clamp flyback controller. 

    Your question is a good one, to which I do not know the answer.  I have sent in a request to our design team to determine this but it may be after a few days next week that I will receive an answer for you. 

    It seems like a reasonable assumption that VDD < 4.3V will also reset the tFDR timer, but we will need some time to verify that assumption. 
    Kindly allow us the time to investigate.  

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    TI__Mastermind 26840 points

    Hello Masashi-san, 

    Actually, I got a reply much sooner than I expected.

    And it is verified that, yes, the tFDR timer is reset (cleared, canceled) before the 1.5s time-out is complete, if VDD falls below the Vvdd(rst) threshold of 4.3V (typ), 3.3V (min).

    Please be aware that the 1.5s time interval is intended to provide a "cool-down" period or rest period between instances where a persistent fault may otherwise cause excess heating or voltage stress.  Repeated manipulation of VDD to shorten the effective tFDR time defeats the intent of this interval, and may increase risk of overstress if not used in a thoughtful, limited manner.

    Regards,
    Ulrich