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ADM7172 - starting with negative biased output

Question asked by MarkusR on Aug 9, 2016
Latest reply on Aug 10, 2016 by rrosario

Due to badly planned power sequencing the outputs (VOUT and SENSE) of an ADM7172 (fixed 3.3V) go down to -1V before the positive power supply (3.7V) is applied to its inputs (VIN and EN). I think the chips that should be powered with 3.3V are now "powered" from ground through a protection diode on the ADM7172 output, and the chip can not start or might even be damaged. -1V is well below the allowed maximum rating of -0.3V.

 

I am hoping to fix this by installing a low drop schottky diode from ground to the 3.3V rail. This should limit the negative voltage to between -0.1V and -0.2V which is inside the maximum ratings.

 

My first question is whether the chip will start with a slightly negative output voltage.

 

And my second question: is the chip likely damaged? Or is not starting expected in this situation? Installing the schottky diode is simple, but replacing the chip on the PCB would be difficult since the exposed pad is very well connected to a ground plane.

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