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STM32H5 VBAT caution in an5711



I am designing some hardware with the STM32H523.

I have a rechargeable ML-Lithium Coin battery directly connected to the VBAT pin of the controller. The battery is supposed to power the RTC when there is no VDD. I would like to use the internal charging mechanism to charge the battery when VDD is present.

In AN5711, I came across the following caution:


I am a bit concerned about this current injection. If it is too high, the battery may get damaged. The recommendation is to "connect an external low-drop diode between this power supply and the VBAT pin."

I understand this as placing a low-drop diode between my battery and the VBAT pin. But which side should the anode be on? And how does this affect the charging/discharging?

If anyone could help me out, it would be much appreciated.



Uwe Bonnes
Principal III

show i.m.h.o. serious degradation with continious chargimg an ML type secondary batterie. Consider your decision carefully!

Thank you for the advice and warning. I had not noticed this problem, or that the battery in my design was no longer recommended for new products. I will now likely go with a battery from the MS-series.