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GATE short failure on LM25069

Di Wang
Expert 1740 points
Other Parts Discussed in Thread: LM25069, LM25066

Hi,

Below is the schematic. I found if I shorted the OUT repeatedly. The GATE will fail and short to GND. Could you help check how this happens?

Thanks.

  • 0
    TI__Genius 12380 points

    Hi,

     

    Can you confirm if it is indeed the LM25069's gate shorting to GND, or is it the iRFS4310PBF's Gate shorting to Source?

     

    If it is the LM25069, it may be damaged if there is very little output capacitance. When doing a hot short test, both wire and trace inductance will cause a transient voltage in the negative direction. This means the OUT pin of the LM25069 can drop below its ABSMAX rating of -0.3V. Having a large output capacitor such as the C11 100uF will help mitigate this effect. Otherwise, we recommend using a schottky diode on the output such as the SK-153TP which we have on our LM25066 EVM (same voltage hot swap but with PMBus capability):

     

    Additionally, C4 would be dumping more energy into the LM25069's gate pin during a hot short. Since it is only 10nF, I would not suspect this to be the root cause; but it would be a secondary area to explore if a schottky and/or C11 do not solve the problem.

     

    Thanks,

    Alex

  • 0 in reply to Alex Triano
    Expert 1740 points
    Hi Alex,
    The FA report shows GATE short to GND. I will follow your advice. Thanks.
  • 0 in reply to Alex Triano
    Expert 1740 points
    Hi Alex,
    If I short and release the output REPEATEDLY and QUICKLY, GATE is easy to fail. After I removed the gate capacitor,C4, it didn't happen again, so C4 might be the cause for failure in this condition.
  • 0 in reply to Di Wang
    TI__Genius 12380 points

    Hi Di Wang,

    I am glad to see that removing C4 prevents failures. However, note there still may be a risk without C11 and/or a schottky present on the output.

     

    A schottky diode is best, but C11 would help mitigate negative voltage on the OUT pin during a hot short.

     

    Thanks,

    Alex