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LM5149-Q1: LM5149Q shows shorted, till a reheat fixes the problem. Happens once a few months.

Tapan Pattnayak
Prodigy 30 points
Part Number: LM5149-Q1
Other Parts Discussed in Thread: LM5149

Tool/software:

HI TI folks,

  I have a LM5149 Q1 24V to 3.3V regulator. I have used that and ran robots for months. However one particular issue we noticed, that occasionally once in a few weeks or months the 3V3 regulator shorts output. Re heating or remounting the same IC make the system up. But power up down dows not solve. 

When this happens the resistance on Output to ground fall to 35 ohm.

We did follow layout guideline. The only thing we misssed is made the IC paddle a solid one, instead of 4 squares..

There are 2 different groups doing independent projects reported that this IC is tough to solder.  Is there any issue. I am attaching the schematic.

  • 0
    TI__Mastermind 33030 points

    Hello Tapan,

    I am not sure I remember everything about this issue, but I know we discussed possibilities at length.  one of your concerns was with the Enable chattering and you felt that issue may be related to this.  Can you please share schematic and confirm that it still may be related to the turn on of this device? Also if you can remind me of our conversation, we had last, I know I discussed a few things to try, would be helpful to know what you tried and what was observed, thanks.

    David.

  • 0 in reply to David Baba
    Prodigy 30 points

    Dear David,

    • I have corrected the wire length as per our discussion. I am attaching the schematic and layout again for your perusal.
    • Carrier_Board_Design_Rev2.3.pdf
    • I am now running with LA probing the EN pin for 1 month and waiting for result
    • Do you see any obvious issue with LM5149Q1 in the scheamtic.

    The Power good from Efuse is turning on 3V3 regulator. Which inturn starts the 5V regulator. 

    From the layout the only difference I see is there are 4 small thermal vias in past below this regulator. Can this be a cause ?

  • 0 in reply to Tapan Pattnayak
    TI__Mastermind 33030 points

    Hello Tapan,

    thanks for sharing the schematic again.

    I noticed the Pgood that enables the LM5149, what is it pulled up to?  Thanks.

    David.