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TPS54821: IC failure issue

EngHW
Prodigy 195 points
Part Number: TPS54821
Other Parts Discussed in Thread: TPS54202,

Hallo, 

Kindly help.

Regards,

Surjit 

  • 0
    TI__Intellectual 2790 points
    Hi,
    Could you provide the schematic and layout?
    If it's only 12V/1A output, TPS54202 may be a more suitable solution. You can find the 12V output circuit configuration in table 2 on page 17. www.ti.com/.../tps54202.pdf
  • 0 in reply to Luke Pan
    Prodigy 195 points

    Hi,

    Thank you for your reply. The Input is +12V at PVIN and output is +11V at TP2, could it be due to voltage stored in C409 and C410? that current flow inside the IC when I start the input supply (0-12V)?

    or It could be ESD? because +11V is connected to I/O through a fuse.

    Is this IC short circuit protected?

    Regards,
    Surjit

  • 0 in reply to EngHW
    TI__Intellectual 2790 points
    Sorry, i actually did not get what you mean. You mean when you apply 12V at PVIN, you only got 11V output, right? What do you mean short circuit short? It will be helpful if you can capture some waveforms and clarify what's the test condition (like Vin, Vout and Iout). The waveform at PH pin is needed.
  • 0 in reply to EngHW
    TI__Intellectual 2790 points
    also what's the part number of your inductor L403 and C409, C410.
  • 0 in reply to Luke Pan
    Prodigy 195 points

    Hi Luke,

    Thank you, I will upload the waveforms as soon as I replace failed IC. L403 = WE-LHMI-74437349033, C409 and C410 = GRM32EC81C476KE15L

    I set the Vsense so to get +11V output, with input at PVIN = +12V, I achieve +11V at PH (So IC works fine). But due to some reason (after some time) I found output terminal PH went to Ground (Could be internal MOSFET failed).

    I have checked all possiblity but could not find possible cause Same issue with 3-4 ICs.

    Please help, if you find any issue.

    Regards,
    Surjit

  • 0 in reply to Luke Pan
    Prodigy 195 points
    Adding to my reply:

    I am looking for the possible cause for this failure,

    1) ESD
    2) Short circuit (PH to ground at external I/O side)
    3) Capacitor C409 and C410 could store voltage and reverse current may flow when input PVIN goes lower.

    I have not use a resistor at PH because I may draw 1-2A current, but I have used a Fuse.

    Please give your views on this.
  • 0 in reply to Luke Pan
    Prodigy 195 points

    Hi Luke,


    May be I found something, C409, C410 are rated 16V and I have +11V across the cap. which may decrease cap. value by 70% according to data sheet. I will replace these caps now.


    What do u think?

  • 0 in reply to EngHW
    TI__Mastermind 18510 points

    Hi Surjit,

    The MLCC DC bias is exactly a little bigger, but it should not cause the chip damage.

    Some query confirm with you:

    1, As you said "I have not use a resistor at PH because I may draw 1-2A current, but I have used a Fuse." , so what's the reistor you mean? and where is fuse you used? we can't see the fuse in you schematic.

    2, How the damage happen? during power up or...?

    3, Did you try to disconnect the Vout with I/O loading, just test the converter to check if is still damage?

    And also If we want to check why it is damaged, better we should catch some waveforms while the damage happen.

    Catch waveform about V-PH(with full bandwith, >500MHz is better) and Vout, also check inductor current waveform if you can.

    Regards,

    Yuchang

  • 0 in reply to Yuchang Zhang
    Prodigy 195 points

    Hi Yuchang,

    I have updated the drawing, I have a load as LEDs and at I/O is also a Load (Kohm). Cause of damage I have to find out (possibly during power up).


    I will try 3rd point now, I have used 3.3uH inductor but my current requirement is less. could this be a reason?

    I have checked damaged IC, low side MOSFET is damaged (High side MOSFET still functional).

    I will upload the wwaveforms after receiving new IC today.

    Kindly looking for your reply.

    Regards,
    Surjit

  • 0 in reply to EngHW
    TI__Mastermind 18510 points
    Hi Surjit,

    Just saw the fuse and LED loading, please try to cut them off with converter and bouble check, and find when the damage happen.
    About the inductor, I think it should be OK, looks the FSW you set(RT 52K) is around 800Khz, 3.3UH for 1A/11Vout is acceptable, but make sure the inductor current is big enough.
    Please also upload your layout for review.

    Regards,
    Yuchang
  • 0 in reply to Yuchang Zhang
    Prodigy 195 points
    Hi Yuchang,

    Thanks, 1A is the maximum I could draw during full Load, without I/O and with Only two LEDs Output would be +11V, 40mA.

    Regards,
    Surjit
  • 0 in reply to EngHW
    TI__Mastermind 18510 points

    Hi Surjit,

    I would like you to check whether the IC will be damage without any loading.

    if not damage, and then you can add loading with E-load to check when the chip damage and catch waveforms.

    Regards,

    Yuchang

  • 0 in reply to Yuchang Zhang
    Prodigy 195 points
    Hi,

    I found the problem, It was in the I/O connector which was making short circuit. TPS54821 has not short circuit protection. Do you know how can I solve this issue. I want to use TPS54821 because I made final layout.

    Regards,
    Surjit
  • 0 in reply to EngHW
    TI__Intellectual 2790 points
    Surjit, I replied your question about TPS54821 in another post, I guess it's the smae one. I'd like you to close this one if no necessary. Thanks.