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LM5122: About Startup problem

ACGUY
Guru 11170 points
Part Number: LM5122

Hello E2E,

Our customer is using the LM5122 for engineering board , the board has a problem at startup often. SS port voltage can't rise up.
I think that it is falling down to slave mode. However, FB port voltage is less than 2V when Vin start input.

Question;
Does TI knows any similar case for other?

Regards,
ACGUY

  • 0
    TI__Guru 59031 points
    Hi ACGUY
    Please check if any protection function is triggered. SS is pulled down during TSD, hiccup mode off, UVLO..
    Regards,
    EL
  • 0 in reply to EricLee
    Guru 11170 points

    Hi Eric,

    Thank you for reply. I obtained two waveforms for each ports. These are same device, same input/output, and using same board.

    In the lower waveform, since the voltage of the SS port is not rising, I think that it is in slave mode.
    However, the voltage of the FB port remains 0 V.

    Question;
    Is the condition for setting this device to slave mode only FB voltage at Vin input?

    Regards,
    ACGUY

    LM5122.pdf

  • 0 in reply to ACGUY
    TI__Guru 59031 points

    Hi ACGUY

    The device will be programmed as a slave if the FB pin voltage is greater than the threshold when the VCC voltage is crossing over VCC UVLO threshold.

    If you think it  is a defected device, please contact your local FAE and hand over the unit to QA.

    Regards,
    EL

  • 0 in reply to EricLee
    Guru 11170 points

    Hi Eric,

    We have not thought it is out of order. Even if LM5122 is replaced, the phenomenon is the same.
    When the Vin input starts, the FB pin does not exceed the threshold value. However, LM5122 is set to slave mode.

    Please let me know your opinion for waveform.
        -  Is it slave mode?


    >> please contact your local FAE and hand over the unit to QA.
    Rejected by local TI.They said in the document that "the quality of this product is stable" and said it would not analyze.

    Regards,
    ACGUY

  • 0 in reply to ACGUY
    TI__Guru 59031 points
    Hi ACGUY
    Please check the Table1 in the datasheet. You can easily check the mode change (Master/Slave) by monitoring SYNCOUT pin.
    Regards,
    EL