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LM3485: LM3485MM/NOPB EOS?

kevin.huang_FJXM
Expert 2925 points
Part Number: LM3485

HI Teams:

         The power supply chip is broken down (between the power supply chip pin 2 and pin 1, between pin 2 and pin 5, and between pin 2 and pin 7 are broken down)

        Please help to analyze where the abnormal voltage or current may cause EOS damage?

  • 0
    TI__Guru 50120 points

    Hello,

    When you say broken down, does this mean a short? 

    From your description of the failure, are you trying to say that U701 (LM3485) has a short between Pin 1, 2, 5, and 7? 

    If so, please help me understand the following:

    • Did you try an ABA swap to check if the failure mode follows the IC?
    • At what point in the board verification/validation was this failure observed? During initial power up or after the part has been running for some time?
    • Are there any visual inspections on the board that short discoloration of components?
    • Has customer checked to make sure that board has proper solder connection and there aren't any solder issues?

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    Expert 2925 points

    HI Jimmy:

                 When you say broken down, does this mean a short? 

                From your description of the failure, are you trying to say that U701 (LM3485) has a short between Pin 1, 2, 5, and 7? 

        yes.

     1.ABA exchange test , the failure mode follows the IC

    2.The customer has completed the production and delivered the goods to the end customer. After use, it is found that

    3.    Are there any visual inspections on the board that short discoloration of components?

         No exception found

    The customer hopes that we can analyze where abnormal voltage or current may cause EOS damage according to the schematic diagram?

    If you need any additional information, please reply

  • 0 in reply to kevin.huang_FJXM
    TI__Guru 50120 points

    Hi,

    Can you tell me the part number of the input capacitor (E701)? I would recommend increasing it to a 47uF with low to moderate ESR and also perhaps a 2.2uF MLCC capacitors on the input. 

    If the +24V comes from a battery input, during a hot-plug event, it is possible for the input rail to surge up to 2X the input and potentially EOS the VIN and PGATE pins which would be over the absolute maximum pin rating detailed in the datasheet. 

    Larger input capacitance will help absorb this voltage surge. 

    Regards,

    Jimmy