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Vdd being held at 0.7V with backup battery fitted

Question asked by Paul on Mar 8, 2012
Latest reply on Oct 20, 2015 by Clive One

When I switch off the power to my STM32F417 with a backup battery connected, the Vdd rail doesn't drop below 0.7V and Vbat falls rapidly. It looks like Vbat is connected to Vdd and is powering the rest of the circuit. If I briefly short Vdd to ground, it seems to sort itself out.

I tried adding a resistor to load up the Vdd rail to see if this would help, but I just got lower voltage (~0.4V) and faster discharge of the backup battery. Seems like it needs a fairly hard short to ground to make it switch off.

Has anyone got the battery backup working on STM32F4?
Do I need to do some configuration in software before this will work correctly?