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LMR12010: Possible component lock up?

Slava Zilberfayn
Prodigy 50 points
Part Number: LMR12010


I have a device in mass production utilizing the chip. Everything works ok for the most part however there were a number of cases (about 20) where the device experienced a complete shutdown and loss of function. Upon receiving failing units from customers they were operating just fine. The number is large enough for use to know the problem is real, but small enough to suspect s/w, the device is deployed in many 1000s for a number of years. The MCU has internal WDT running. So...

The problem appears to be related to AC power surges. In one case it was directly confirmed by customer. In some other cases several units failed in the same way at the same time.

Is it reasonable to suspect a lock up of the LMR12010, where it does not output any voltage and consumes very little current?

On the schematics below X1 is taking power from a Meanwell brick AC-DC power supply. In all case customers we instructed to disconnect input AC, and leave it like that for at least a minute. It never helped. However as I mentioned on return to factory all devices functioned ok.

My theory is that LMR12010 locks up and stays that way indefinitely. Disconnecting AC does not help because output cap of the MW power supply keeps the LMR12010 under voltage. Is that a plausible scenario?

Thank you.

  • 0
    TI__Genius 14455 points

    Hi

      The failures of 20 units is that happening now, or is that the cumulative number of the units over years?

    Regards,

    Gerold

  • 0 in reply to Gerold Dhanabalan - High Performance Radar
    Prodigy 50 points

    That is a number of this kind of failures over last 9 month or so.

  • 0
    TI__Mastermind 27270 points

    Slava,

    I understand this design is in production but was this tested for line/load transients or stability? Usually, this device can handle one L-C filter at the output but the scheamtic you shared has 2 LC's at the same corner frequency. The internal compensation will not be able to compensate for that especially under sudden input or load changes. And that can lead to odd behaviors. The L value looks really large (22mH) for such a high switching frequency depending on whether you are using the LMR12010X (1.6MHz) or LMR12020Y (3MHz) version. I would expect something in the range of 1uH-10uH. Also, I cannot read the input cap (C5?) value - this needs atleast 10uF input cap. 

    Since you mentioned all returned ICs work when you try it - Is there a possibility of issues on the customer board (related to manufacturing or other design failures) or any component damages other than IC that could be causing incorrect operation? If the customer has more than 1 such design, they could try swapping the failed design IC on a working board and see if that works. If there is a set of steps to be able to reproduce the loss of operation, capturing key waveforms of this design may give you some insight as well. Finally, I am also trying to find from our quality team if there are any reported issues similar to this on these parts.

    Regards,
    Amod 

  • 0 in reply to Amod Vaze
    Prodigy 50 points

    Thank you for the info.

    Sorry the schematics was not quite accurate. The actual inductor used is NR6028T2R2N, 2.2uH. Input cap is 22uF, 35V.

    Note that we did not get back just the IC. Entire product was returned, and they all functioned fine, not just the IC. Entire product was found completely functional. So no, there is nothing damaged on the boards.

    Yes the device was tested for AC-line surges, among other things. I don't remember the standard off the top of my head right now. But I'm sure we tested to at least 2kV between any two pairs (L-N-G). 

    To be clear, I do not completely rule out MCU lock up. Just looking at possible scenarios. I've instructed support personal to ask customer to measure the 5V output of the LMR12010 next time they get a report of this kind of problem.



  • 0 in reply to Slava Zilberfayn
    TI__Mastermind 27270 points

    Thanks for the information Slava. The LC looks fine if it is a single-stage. Is there 2-stage LC filter at the output? I checked with quality team and no such lockup issues have been reported in the past for the LMR12010. Yes, it is a good idea to track the VIN, SW, VOUT waveforms if there is a failure again during the time of failure and when the IC is functioning fine. Let us know when you get any update on this.

    Regards,

    Amod