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TPS54325

James Dowle
Prodigy 90 points
Other Parts Discussed in Thread: TPS54325

Hi

I have a PCB with 4 TPS54325 converters all operate off a 13V5 rail two output 1V8, one outputs 3v3 and on outputs 5V4, I'm having troubles with the 5V4 one being damaged during turn on sometimes, it gets into a state when it will start to turn on and shut down and then retry, once it gets into this state whatever I've done I can't get it to start unless I remove the IC and replace it. I've included the circuit I'm using below, The two diodes above it supply a very low current ~50uA supply, I still have the problem if I remove these. My other supplies are almost the same but have some changed component values to suit there lower voltages. The output of this supply drives a number of linear LDO regulators. 

 

Any advice on what might be causing the problem would be greatly appropriated.

Thanks James

  • 0
    TI__Guru**** 191445 points

    What is the purpose of the added diodes and capacitors.  try removing D214, C2319 and C2320.

  • 0 in reply to JohnTucker
    Prodigy 90 points

    I have tried it without the extra diodes and capacitors present and still get the same issue

    The diodes and capacitors are generating a low current 18 volt supply.

    Thanks

    James

  • 0 in reply to James Dowle
    TI__Guru**** 191445 points

    Can you post some waveforms that illustrate your issue?

  • 0 in reply to JohnTucker
    Prodigy 90 points

    I'll capture some once I have the issue occurring again, my boards are currently working but I've haven't tried anything new so expect it to occur again. 

    Thanks

    James

  • 0 in reply to James Dowle
    Prodigy 90 points

    I've got another chip that has stopped working but this has different symptoms then the others , I'm getting nothing out of this one, every pin except VCC, VIN and EN is sitting at ground on this one, have you any suggestions on what I could look for on the circuit or changes I could make, Sorry no wave-forms still as I've got a completely dead chip this time, I've included a top and bottom side layout I'll see if I can get an image out that has the copper in a darker color it's not the easiest to see on these.

    Thanks

    James

    . 

  • 0 in reply to James Dowle
    TI__Guru**** 191445 points

    What happens if you pull EN up to Vin?  Can you cycle Vin?

  • 0 in reply to JohnTucker
    Prodigy 90 points

    EN is pulled up to VIN, I have cycled VIN with no change, I don't get anything even during turning on VIN.

    I have a number of boards that are currently running fine but have had to replace the IC on a few of those as well, I'm in the process of preparing for a PCB update and have a good opportunity to make changes, but would like to get an understanding of what might be causing the damage, I could make some measurement on a board that is working fine, to see if there is anything unusual going on, if you have any particular signals that you would like to see and at what time let me know.

    James

  • 0 in reply to James Dowle
    TI__Guru**** 191445 points

    These devices have so far proven very robust.  There is not any significant history of failure.  I would recommend taking some start up waveforms to look for something unusual.  You could submit some of your failing parts for FA by contacting your local FAE.  As you can probably imagine, it is rather difficult to troubleshoot these types of problems via forum posts.  But if you can supply some waveforms, I'll take a look.  Can you tell me anything about your application?  Are you doing any hot plugging?

  • 0 in reply to JohnTucker
    Prodigy 90 points

    Hi

    I've captured some waveforms, there is an odd glitch on SW at times during start up. 

    channel 2 (green) is VCC, VIN and EN

    channel 3 (pink) is Vout

    channel 4 (blue) is SW

    channel 1 (yellow) is softstart

    all of the start up

    during the early part of start up

    Later in start up (glitch on SW)

    More detail of glitch on SW

    during operation

    tel me if any other waveforms would be useful.

    Thanks

    James

  • 0 in reply to James Dowle
    TI__Guru**** 191445 points

    That start up look ok.  I am not sure about that skipped pulse though.  I'll get back to you on that.

  • 0 in reply to JohnTucker
    Prodigy 90 points

    Hi John

    Since all our boards now have our pre-regulator between this and the bench power supply we are no longer having any issues with the TPS54325 devices being damaged, it appears to have been caused by the bench power supplies we're using.

    Thanks

    James