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TPSM84209: Enable pin tied to input supply outside of Abs Max spec

UA&A_CodyDowling
Expert 1006 points
Part Number: TPSM84209

TI Team, 

In a recent design, we tied the enable pin of the TPSM84209 up to the input supply (25.5VDC) out of habit. We've since learned that this pin has a 7V abs max rating. We've found that approximately 7 boards have had no issue with this arrangement with several hours of testing logged.

Can you explain why we might find that this arrangement doesn't seem to be a problem for the device?

Thanks in advance, 
Cody

  • 0
    TI__Genius 17905 points

    Hi Cody,

    You may not (yet) have seen issues with the small sample of boards you have tested, but I expect that you will see issues eventually by exceeding the abs max rating. There could be excess current flowing into the pin and the device that may not be causing immediate damage but could impact long term reliability - you might measure that the input current is considerably higher than you would expect (Iin = Vout * Iout / (Vin * expected efficiency)) as a sign of this. Even if there are no telltale signs of a problem, I would highly recommend adding a resistor divider to bring the EN pin voltage within Recommend Operating Conditions max of 6V.

    Regards,
    Kris

  • 0 in reply to Kris F
    Expert 1006 points

    Hi Kris,

    Thanks for your response. Yes, of course we will fix this in the next rev. I was just surprised that it survived at all... :) 

    In agreement with your point, excessive dissipation was exactly what we noticed- the device was far hotter in thermal images than what was merited by the output power. That is what prompted the investigation and discovery.

    Thanks for the feedback, and have a great weekend!