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LM5085: The chip is destroyed when powered up

user5811580
Intellectual 700 points
Part Number: LM5085


Hi

I'm using LM5085 to make a buck converter.

The input voltage is 60V , the output is 48V and the Current is almost 7A.

I have used 3 LM5085 totally, but there is one getting destroyed when powered up.

Please check the schematic listed as below.

The PCB is listed as below

Would you please have a check?

  • 0
    TI__Expert 6245 points
    Hello Wu Shi,

    On your schematic,

    1) Your VCC cap is small. Recommended is 0.47 while your value is 0.047. Since your operating frequency is relatively high, an 0.47 uF should be used.
    2) Could you please let us know what power FET you are using.
    3) Could you please let us know the manufacture’s part number is for C311.

    Layout,
    1) You are using a package without a DAP at high frequency – is your chip getting hot?
    2) Ground connection looks poor, how many vias do you have?

    Regards, Robert
  • 0 in reply to Robert Blattner
    Intellectual 700 points

    Firstly, thanks a lot for the response.

    1) Your VCC cap is small. Recommended is 0.47 while your value is 0.047. Since your operating frequency is relatively high, an 0.47 uF should be used.

    A:OK.I'll have a test with 0.47uF
    2) Could you please let us know what power FET you are using.

    A:The FET we used is Si7469 ,released by Wishay. This FET is also recommended by ti on the reference design.

    3) Could you please let us know the manufacture’s part number is for C311.

    A:In fact,C311 is a electrolytic capacitor of 10uF.

    Layout,
    1) You are using a package without a DAP at high frequency – is your chip getting hot?

    A:In fact, we wants to buy chips with a DAP. However, the seller sent us samples without DAP.

    We have not tests with the load. Now, the chips are not hot without any load.

    2) Ground connection looks poor, how many vias do you have?

    A:Have you paid attention to the blue part? It's a big ground just under LM5085.

    There is only one via in this part.

    Update:

    We have changed C317 to a electrolytic capacitor of 10uF too.

    Of course, we also changed the damaged LM5085.

    Now, we can get the right output without any load.

    Do you still have any suggestions?

     

  • 0
    Intellectual 270 points

    Hi 

    Have you solved this problem?

    I have the same problem.

    Chips works for a few seconds and then dies. (VFB = 1.25V output is as expected.)

    Not applying much load 10-100mA

    I'm seeing VCC = 12V not the stated 7.7V to 8.5V Max

    Then VFB drops and output drops.

    Any suggestions?

    Hard to test because chips keep dying.

    Thanks

    Andre

  • 0 in reply to Andre Schoeman
    TI__Expert 6245 points
    Hello Andre,

    We are not supposed to leave threads open to debug multiple customer’s circuits. Please open a new thread.
    In the new thread or by email to Robert.blattner@ti.com please provide a schematic and BOM. I am closing this thread to prevent multiple debugs per thread.

    Your circuit’s behavior may not have the same root cause as that for Wu Shi’s circuit which appeared to be a problem with the BOM.

    Regards, Robert