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LP3872: Leaving the ERROR output pin floating

Jerry Lipson
Prodigy 100 points
Part Number: LP3872

Why does the datasheet state that the ERROR output pin must be connected to ground if not used?

Does it cause a problem with the regulator if left floating?

  • 0
    TI__Mastermind 18466 points

    Hey Jerry, 

    The risk is that ERROR voltage will be set based on external leakage. If the ERROR voltage does not violate ROC conditions, then there is no risk.

    Best,

    Juliette

  • 0 in reply to Juliette
    Prodigy 100 points

    Hello Juliette,

    What is ROC?

    How would you determine external leakage and what could cause the external leakage?

    Also how would the fixed output voltage of the regulator be affected by not connecting ERROR since the part datasheet doesn't show any feedback path for the open-drain ERROR output?

    I have a number of these parts on a few different assembled boards and hadn't noticed the note about trying an unused output to ground and want to make sure I won't see any intermittent issues with the boards.

  • 0 in reply to Jerry Lipson
    TI__Mastermind 18466 points

    Hey Jerry,ROC is Recommended Operating Conditions. 

    external leakage can come from a contaminated board creating paths to the pin where they might otherwise not be.

    do you have any signals on your board that would violate the recommend operating conditions?

  • 0 in reply to Juliette
    Prodigy 100 points

    No, I am just creating 3.3V & 2.5V supplies from a main 5V input. Current draw will be well below maximum at about 100 -200mA.

    Unlikely to see any contamination on the boards which will be in a ventilated enclosure.

  • 0 in reply to Jerry Lipson
    TI__Mastermind 18466 points

    Hey Jerry, 

    I will confirm tomorrow if this is ok. I think it will likely be fine. 

    Best,

    Juliette

  • 0 in reply to Juliette
    TI__Mastermind 37005 points

    Hi Jerry,

    I have reviewed this further.  If the ERROR pin is floating and it has transient signals on it for any reason, that can inadvertently cause internal circuitry to react and possibly change the behavior of the LDO.  By connecting the ERROR pin to GND, you eliminate these concerns.  If you leave the ERROR pin floating you will want to ensure that no accidental transients can couple into this pin.  This coupling will be in the form of some sort of EMI induced path: capacitive coupling through the internal plane layers, or radiated coupling if you have a high frequency radiator signal nearby the LDO's.

    All in all, it may be unlikely that you will have an issue with the pin floating but you'll need to do some additional evaluation on your system to eliminate the low risk.

    Thanks,

    Stephen