VBAT Channel Monitoring in the MCU

[ASiva.1]

Datasheet of STM32WB55 mentions that the Maximum voltage that can be given to VBAT is 3.6 V. But, it is also said that there is an internal voltage divider so that voltage to the ADC is 1/3 of the voltage at the VBAT pin So, is it possible to connect 4.2 V LiPo battery to VBAT pin for voltage monitoing?

[Ons KOOLI]

Hi ASiva.1,

Can you please share a screen shot from the datasheet where you find the info :"But, it is also said that there is an internal voltage divider so that voltage to the ADC is 1/3 of the voltage at the VBAT pin"

Best Regards,

Ons.

[Peter BENSCH · Accepted solution]

As the name suggests, the maximum rating must not be exceeded, otherwise the MCU can be damaged, a LiPo must therefore not be connected directly to the VBAT pin.

The voltage divider is necessary to adapt the (possibly) high voltage of e.g. 3.6 V to the measuring range of the ADC, which is given by the level at VREF+.

BTW: as long as VDD is present, the voltage source is completely disconnected from VBAT in order to avoid even small discharge currents from the battery/supercap and to extend its life time.

When your question is answered, please close this topic by choosing Select as Best.

/Peter

[waclawek.jan]

Not in DS, but RM:

Nothwithstanding, the absolute maximum limits still apply, as Peter noted.

Truth to be said, the Absolute Maximum for VBAT is 4.0V - but still more than a LiPo battery will provide.

JW