STM32H5 VBAT caution in an5711

[Ral]

Hello,

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]

https://mediap.industry.panasonic.eu/assets/imported/industrial.panasonic.com/cdbs/www-data/pdf/AAF4000/ast-ind-174508.pdf

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

[Ral]

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.