• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 63 subscribers
  • Views 433 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMZ30606: What could cause a short circuit?

Jon Mason
Prodigy 190 points
Part Number: LMZ30606

We have designed this part into one of our products. We have had 2 customer returns with the same failure. Basically there's a pretty catastrophic short between the following pins: VOUT, PH, VIN, AGND. Obviously that's very bad news.

There's no obvious external damage and it's definitely the chip itself. I've probed it after removing it from the PCB.  But it's not at all obvious how it's happened. 

I've attached the schematic - any ideas what the failure mode might be?

  • 0
    TI__Guru 50120 points
    Hi Jon,

    Can you provide the assembly solder profile? Also what is your operating conditions? (VIN=5V, VOUT=?, IOUT=?). Is this failure a time zero failure or does this happen some time after operation?

    Regards,
    Jimmy
  • 0 in reply to Jimmy Hua
    Prodigy 190 points
    VIN should be 5V. VOUT = 3.3V. IOUT = 0 to 2A
    When these left our facility they were fully tested, so this is a failure in the field, not at zero hours.

    I'm just trying to figure out what could have caused the device to short in that manner?
    Would over-voltage do it?
    Reverse polarity is impossible, because of the protection diode.
    Over-current on the output is impossible by design I presume? What happens in the event of over-current? Does the device shut down? Or is some sort of thermal runaway possible?

    Thanks for your help.
  • 0 in reply to Jon Mason
    TI__Guru 50120 points

    Hi Jon,

    It will be tough say without taking this through failure analysis. I can say I've seen issues where VIN shorts to VOUT because of an EOS damage. Over-voltage over the recommended input range of the part could cause damages in the internal inductor and result in shorts. The OCP characteristic can be seen in Figure 26.

    Can you confirm that the VIN at the customer field site is within the 6V input voltage recommended range? 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points
    Hi Jon,

    Can I get an update on this? As stated previously, EOS damage on the part may result in those failures that you see.

    Regards,
    Jimmy
  • 0 in reply to Jimmy Hua
    Prodigy 190 points

    Hi Jimmy,

    I don't really know how to proceed. EOS is possible but I can't prove it. If you think over-voltage at the input might result in shorts as described, that's probably it.

    Regards,

    Jon.

  • 0 in reply to Jon Mason
    TI__Guru 50120 points

    Hi Jon,

    I recommend sending a few unmodified failing boards in for failure analysis. Please go through the "Failure Analysis" to get more information on the specifics and "Customer Returns" for the request.

    Additionally, you may want to add an electrolytic input bulk cap to help prevent future overvoltage spikes from happening. This assumes their input source is fixed at 5V but might momentarily spike during startup/turn-on.

    Regards,

    Jimmy