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TPS55340: One Boosted, the others failed.

Jim Lynch
Prodigy 40 points
Part Number: TPS55340

I've TPS55340s on multiple boards that suddenly don't work.

I used the Webench design tool, purchased the dev board and everything worked. I had 15 boards built using the design. The first one tested perfect.

The next 4 boards have all failed. When they are powered on, they start to audibly ring. They may or may not stop ringing. They don't output the boost voltage. 

One of them, I turned it on, the meter read the output at 15VDC briefly, but then it stopped and went to the input voltage.

The first board tested is still silent and works great. About all I can figure, is I suddenly have a bunch of dead chips.

Input voltage is 12VDC @ 100kHz

Output voltage should be 15VDC

The enable is tied to the 12VDC rail and the soldering job the fab house did looks great. I've gone as far as, just to verify, as to reflow one of the boards. Still doesn't work. 

ESD precautions have been used when handling the boards. 

At present, best guess is I got a bad batch of TPS55340? I don't have any spares to replace for testing. I do still have other boards to test, but was hoping for something optimistic first. 

  • 0
    TI__Mastermind 40080 points

    Hi Jim,

    What is 12VDC @ 100kHz mean?  is it a pulsed volatge with 100kHz frequency?

  • 0 in reply to Helen chen
    Prodigy 40 points

    Helen, that is the switching frequency of the AC/DC supply that supplies the +12VDC to the board. It is actually pretty clean on the scope and could be excluded in my comment. 

    The +12VDC goes in and +11.93VDC goes out. I don't see any signs that the TPS is try to turn on. I read another forum where they found the output diode was dead, but even they had a blimp on power up that the TPS was trying. Mine just looks like it is totally dead.

    Thanks,

    Jim

  • 0 in reply to Jim Lynch
    Prodigy 40 points
    I've troubleshot and tested further.

    Per the Webench design, it spec'd using the SS24FL diode. I swapped a SS24FL from a known working board with one from a non-working board. The working one quit working and visa versa. I swapped them back. Then replaced the suspected failed SS24FL with a B340LA. The failed board now works. I repeated replacing the SS24FL on another non-working board with a B340LA. It now also works.

    It appears these all failed do to brand new SS24FL's being either defective or somehow being damaged by....???.

    I don't know the true resolution of the issue as I'm not sure the nature of the failure of the SS24FL. But at present, the solution to the TPS55340 not boosting from +12VDC to +15VDC appears to be due to failed diodes.
  • 0 in reply to Jim Lynch
    TI__Mastermind 40080 points

    That's fine. But SS24FL looks OK for you application. at least, its voltage rating should be OK. What is your output current? if the output current is also OK, maybe this diode has been damaged beore you solder it on the board.