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LM43603: LM43603 damaged

Jason Fan
Intellectual 1705 points
Part Number: LM43603

Hi  TIers:

I met a issue on charging board for the automotive, the LM43603 is used to convert the 12V to 5V for the external USB slave device. The schematic is below ,

The issue is that the LM43603 will be damaged during frequently plugging in/out the 12V input . The phenomenon of the failed sample is the SW to VIN, GND, VCC is shorted . And I also ask them to check the input voltage and output voltage when plugging in/out the power .

It indicated that there is under voltage on the VIN and Vout ,the lowest voltage of the 5V will be negative which could damage the chip.

So my question are : a)  That's the reason cause the chip damage when plugging in/out the power

                                   b) How to eliminate the bounce of input ?

Blue: 5V output 

Yellow: 12Vinput

SWPA6045 Series.pdf

  • 0 in reply to Jason Fan
    TI__Guru 68345 points
    Either an over-voltage or a large negative voltage can damage any regulator.
    It is possible that you are getting an over-voltage ring from the ceramic input caps
    and the power line inductance. This can be controlled by adding a 47uF to 100uF Al. input cap.
    This cap will add ESR to the input and help to damp any ringing on the input line when plugging in
    the regulator.
    If you believe that there is a large negative voltage present, then a Shottky diode across the input
    should help.
  • 0 in reply to Frank De Stasi
    TI__Intellectual 1705 points

    Hi Frank:

    Thanks for your reply.

    Customer has add 68uF Al input cap on the input ,and the input ringing is still there ,please see the attached plot. The negative voltage is much higher than the chip could support.

    There are constantly coming out the new failed in customer side , we have to find out the root cause asap, Any information you need, please let me know.

    Yellow: Input      Blue: SW

  • 0 in reply to Jason Fan
    TI__Guru 68345 points
    It sounds like you have discovered the problem. If the positive voltage is not too great, then the negative swing will
    have to be eliminated. I would try a Shottky diode across the input.
  • 0 in reply to Frank De Stasi
    TI__Intellectual 1705 points

    I don't know if you can see the schematic attached in my previous reply , it's obvious that there is a Shottky diode in series with the input , the part number is SMB SS26T3 .

  • 0 in reply to Jason Fan
    TI__Guru 68345 points
    I was referring to a diode in parallel with the input to clamp the input from going negative.