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Reverse current protection for disabled LTM4625?

I'd like to use a LTM4657 to create a 3.3V rail from a 12V barrel jack.  This barrel jack supply might not exist, and the 3.3V might be created somewhere else.  I've tried to make it so the LTM4657 will bring RUN low when the barrel jack power supply is absent (see the attached pdf).  I know the load switch following the module won't stop reverse current.  Will the output of the LTM4657 be high-impedance when the input is zero and RUN is held low?


  • Hi John,

    Once VIN goes lower than VOUT, you'll have a discharge path through the body diode of the top switch. Please use block diagram in page 7 of datasheet to picture this. D7 in your schematic will prevent current flow through R112, R114. With 3.3V, I don't see any potential issue this can cause as it is quite low compared to Abs Max ratings of the pins. Better to double-check for transients in testing.