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UCD3138A: UCD3138A STARTS UP INTO ROM MODE WHEN AMBIENT TEMPERATURE IS BELOW -10'C

jun yin
Intellectual 875 points
Part Number: UCD3138A
Other Parts Discussed in Thread: UCD3138,

Hi Sir:

we have write check sum so there is no way it could go into ROM mode;

when ambient temperature is high, it works normally; while when ambient temperature is below -10'C, it starts up into rom mode and stays in that way; PMBUS works and we can command it into program mode;

we have changed UCD3138A to UCD3138 with same firmware, it works all the time;

why this happened?

  • 0
    TI__Expert 3200 points
    Hi Jun,

    I moved your question into the Digital Power Forum where your should be able to receive better support.
  • 0 in reply to Brian Johnson96
    TI__Genius 14580 points

    Hi, Jun,

    Please send V33D start up waveform to s-xu@ti.com.

    Regards,
    Sean

  • 0
    TI__Genius 17090 points
    Obviously some step in the startup from Boot ROM to running is failing. I assume that if you raise the temperature, the part will then start fine, proving that the checksum is good.

    It's hard to tell what the exact cause could be without looking at it. We have found a very small number of parts which actually have a hardware failure at low temperature. However most of the issues like this can be solved by better board layout and more power supply bypass capacitors. Because of production variation, some chips are more susceptible to noise than others. And generally noise gets worse at lower temperatures, because RDSon gets lower, and the FETs switch faster.

    My colleague Sean will reply too, he's the layout expert, among other things.