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Original question:

UCC256403: External Shutdown function

UCC256404: Need a way to shutdown UCC256404 with external temperature trigger

UA&A_CodyDowling
Expert 1006 points
Part Number: UCC256404
Other Parts Discussed in Thread: TMP392
I noticed that there is an over-temp error circuit and in the tidrt45a reference design. I was hoping to use it as an example to follow to create on over-temperature shutdown on the UCC256404. However, I've been trying to simulate that tonight and it doesn't appear to be working. I'm not sure how the mosfet which is meant to clamp the FB pin would ever turn off (at least according to the simulation).

But, I got to looking at the TMP392 device, which I would like to use for the over-temperature error trip device, and it has an open drain output. It seems that I should be able to hook it's output to the FB pin directly, and when the OTE trip threshold is reached, the TMP392 will pull it's output low and cause the UCC265404 to shutdown, right?

I looked in the data sheet for the TMP392 and the leakage seems to be really low (on the order of 1uA). Do you see any issue with just connecting it directly to the feedback pin?


If this doesn't work, can you please recommend a way to shutdown the LLC (or limit the power) based upon a temp sensor triggering?
  • 0
    Expert 1006 points

    In looking at this again, it seems like there are a few places that the LLC could be brought to a stop, without having to muck with the sensitive FB pin. Perhaps we could use the TMP392 output to drive a mosfet tied to the BLK pin. When the mosfet closed, it would allow us to emulate an under voltage condition and shut the LLC down. This would allow time for the PFC and the LLC to cool down while the hysteresis in the TMP392 recovered the over-temperature error. 


    Seems like a better way, right?

  • 0 in reply to UA&A_CodyDowling
    TI__Mastermind 27095 points

    Hi Cody,

    I would consider tying to the BLK pin to be a better option than the FB pin. Using a MOSFET to pull down the BLK pin is a common scheme for enable/disable of the LLC.

    Best Regards,

    Ben Lough