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TPS27S100: Questions about xFAULT and some On/Off cycle Testing

Darren (FAE)
Expert 5483 points
Part Number: TPS27S100


I am supporting a design currently evaluating the TPS27S100.

The device is undergoing a specific evaluation, where, while the driver is ON and sourcing current, it experiences periodic Shutdown (driver output = OFF) for short intervals. The test just checks to make sure the driver output really is OFF.

Test #1:
Interval = 1[s]
OFF = 30[ms]
During this test, it seems the xFAULT signal is asserted at times. This has been confirmed by the system response, which reacts to an xFAULT condition; there is no waveform yet.

xFAULT may be asserted due to any of the following (4) points.
1) Short to GND
2) Open load, Short to supply
3) Thermal shutdown
4) Thermal swing

Assuming this has some relationship to the device overheating, is there any way to differentiate in the lab between a (3) fault, and a (4) fault?

  • 0
    TI__Genius 16390 points

    Hi Darren,

    From the device point of view, I don't think they can be differentiated. However, if the device is turning on and off repetitively, then I think it's most likely a thermal shutdown, as thermal swing should only happen once.

    One thing you can do to verify is use the thermal camera to get the device temp, and see if it's close to the thermal shutdown temp specified in the datasheet.

    Please let me know if you have additional questions/comments.

    Regards,

    Yichi

  • 0 in reply to Yichi Zhang.
    TI__Expert 5483 points

    Hi Yichi,

    Sorry, I wasn't clear. The device is not shutting itself down, they are toggling the device output ON/OFF.
    There are a lot of unknowns I haven't confirmed, sorry...

    Let me try to explain a different way...

    The TPS27S100A is "ON" for 970ms, and "OFF" for 30ms. This is toggled by the EN pin. While "ON", device sources ~2A current.

    During this "ON" and "OFF" toggling, they are checking to make sure the device really does get turned off.

    This of it like a burn-in test, or a test of 20,000 cycles On/Off.

    The issue is, xFLT goes Low sometimes during this test.

    They want to identify why, and believe it could be related to temperature rising.

    Is Thermal Camera / Thermocouple Probe the only way to identify if the fault is caused by overheating?
    Is there any way to time the xFLT asserted condition and infer, based on length of the xFLT assertion, which thermal protection was triggered?

  • 0 in reply to Darren (FAE)
    TI__Genius 16390 points

    Hi Darren,

    Understand now. I don't think we can differentiate the two from the device output signal point of view. However, the thermal swing really would happen in the first couple cycles as the FET temp goes up sharply while the controller hasn't been heat up yet. During the burn in process, any thermal fault should be the thermal shutdown fault.

    Customer can use the thermal camera to verify this assumption, and they can assume it's a thermal shutdown during burn-in process if camera results align with our assumption.

    Regards,

    Yichi