Dear All, in STM32MP15x application notes I found capacitor parallel with the battery(VBAT pin) . I would like to know what is the practical reason to place capacitor next to a chemical battery? Maybe that capacitor can be omitted? Regards, PL

[Lacc]

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[PatrickF]

Hi,

it depend on your battery size and technology, if chosen battery has relatively low internal resistance during life time (roughly < 50ohms like a CR2032 coin cell), capacitor could be skipped.

Although current on VBAT is very small in many cases, there is some small peak of current (due to RTC activity or active TAMP pins toggling) which might need to be filtered by the capacitor, especially when the battery is near their end of life. The capacitor might increase (a bit) the time where the low-bat is detected by your system.

Capacitor type should be carefully checked to avoid additional leakage which might ruin the battery lifetime (especially at high temperatures).

Even if not intended for that purpose, capacitor is useful as additional ESD protection when battery is swapped without care by the user.

Very large capacitor could also help to maintain VBAT in case of battery swapping (but this is not the main goal, and large capacitor might have more leakage).

Regards.