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TPS54386: why output is abnormal when temp is below -15℃？

Yuan Tan63
Expert 3280 points
Part Number: TPS54386

hi,

the SCH is as below:

but when environment temp is -15℃, the 3.3V output drops and result in reset IC response.

here is the waveform: (yellow is Pin13, green is 1.2V output, blue is reset signal)

from datasheet, it shows Tj is -40~+150. 

so why 1.2V output is abnormal when temp is below -15? the temp is lower, the drops is worse. And 3.3V also shows low temp sensitive but not such bad like 1.2Voutput.

thank you!

Best regards,

Yuan Tan

  • 0
    TI__Mastermind 30530 points

    Hello Yuan,

     

    The TPS54386 can handle down to -40C and up to 150C junctions. And the device is characterized from -40 to 125C. So at -15C should not cause any reset to the device.

    Please look at the external component (inductor, capacitor, and resistors) if they are rated to that temperature and see the derating values of them at -15C.

    The second factor, how are you testing this? Is it in the oven, if so, please make sure the humidity factor is not causing shorts in your board as you test his. I have seen before, when the board is tested in over and high humidity, as the temperature drops pockets of frozen water is created.

     

    Thanks!

    Tahar

  • 0 in reply to Tahar Allag
    TI__Expert 3280 points

    Hi Tahar,

    Thanks for your reply.

    But in -15℃, when customer change the input voltage as 8V, duty ratio above 15% , the output is normal. do you have further suggestion for that?

    thank you!

    Best regards,

    Yuan Tan

  • 0 in reply to Yuan Tan63
    TI__Mastermind 30530 points

    Hello Yuan, 

    This tells me that the rating of the external component is de-rated over voltage and temperature. Please check that up. 

    Thanks! 

    Tahar