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LM3671MF-3.3

Heber Redd
Prodigy 10 points
Other Parts Discussed in Thread: LM3671

While using the LM3671MF-3.3 in production, we are having an issue when we flash the MCU that is being powered by this part which causes a LM3671 component failure (short on output).  Any ideas why this is happening?

  • 0
    Intellectual 510 points

    I am also currently investigating an issue with this same part where we have an output short circuit. I was about to start a new post when I saw yours.

    We have shipped 1000s of a board using this design and to date had just three failures but I am still trying to understand where the weakness is in the design.

    The output of the LM3671MF-3.3 is shorted and replacing the part the board boots correctly.

    I have ran load step tests, power up tests, over-current tests and the part behaves perfectly - the load step response is really good. The power up seems clean.

    The only issue in my design that I have seen is that the enable pin is tied to Vin which is not recommended - it should be enabled only when Vin has reached the minimum operating voltage.

    The fault symptom for us was that the customer turned the product off and it would not start up again - almost as though the turning off caused this.

    In terms of your issue - do you have the LM3761 powered during programming? The SW pin should not be above the VIN pin + 0.2V. So if there is power on the output but not on the input to the LM3671 then you may have an issue.

    Also some programmers pull a pin up to a higher voltage to put into programming mode. It might be worth checking the 3.3V rail during programming with an oscilloscope to see what happens.

    Mark