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TPS272C45: Fault is turned off during thermal shutdown

Miroslav Mrdjan
Prodigy 175 points
Part Number: TPS272C45

Hello,

It is written in the datasheet that FLT will not reset until VOUTx has risen to VVS – 1.8 V.

We are keeping output shorted with a wire all the time and behavior is such that device goes in and out from fault periodically. At the beginning device shows fault state normally. After it starts with "non fault" state, by percentage, device is much longer in fault state - lets say 80/20%. 
But as more and more milliseconds pass, this relation is becoming 40/60% in "non fault" state favor.

Device is kept in auto-retry mode all the time.

This is something related to thermal shutdown obviously, I'm just not sure why it shows that all is fine when obviously it is not. Vout has no chance to reach voltage that will reset Fault signal as it is short wired.

Best regards,
Miroslav

  • 0
    TI__Mastermind 34905 points

    Miroslav,

    There are two types of thermal shutdown on the device: relative thermal shutdown and absolute thermal shutdown:

    I believe what you are seeing initially is the device going in and out of relative thermal shutdown. In this case, what happens is that the temperature sensor on the FET has a drastic mismatch with the temperature sensor on the controller. In this case, the device assumes something is systematically wrong and turns off. Once the device reaches absolute thermal shutdown, the device goes into the hysteresis mode described above with different timing.

    Best Regards,
    Tim

  • 0 in reply to Timothy Logan
    Prodigy 175 points

    Hello Timothy, 

    Thanx.

    We are doing periodical check of fault at the output. Not managed by interrupt or similar.
    So, in theory, it could happened that we never detect error due to short wiring of output?

    Best regards,
    Miroslav

  • +1 in reply to Miroslav Mrdjan
    TI__Mastermind 34905 points

    In theory, depending on how often you poll, you could conceivably miss a fault on the output. The FLT pin will be a global fault that would OR all of the channel faults together, however, so it would be best to have some sort of interrupt based on the FLT pin.

    One thing to note is that even though you could theoretically miss the fault, the device would still protect itself. Current limits, thermal protections, etc. will still be implemented regardless if DIA_EN is high or low.