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Associate II
October 10, 2016
Question

VBAT for RTC backup

  • October 10, 2016
  • 5 replies
  • 1402 views
Posted on October 10, 2016 at 13:12

Hello, should i connect 3V battery to Vss or Vssa for RTC backup (external 32768 resonator)?

#too-vague #stm32-vbat-rtc
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5 replies

slimen
slimen
Visitor II
October 10, 2016
Posted on October 10, 2016 at 16:09

Hello,

Refer to the product datasheet and related reference manual to have the information you are looking for.

Regards

Tesla DeLorean
Tesla DeLorean
Guru
October 10, 2016
Posted on October 10, 2016 at 17:59

What STM32 part? Most have a VBAT pin. Those that don't expect to be battery powered (ie L series), in which case you'd want a diode arrangement into VSS/VSSA and put your device into a low power mode when the primary supply goes away.

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mailboxAuthor
Associate II
October 11, 2016
Posted on October 11, 2016 at 09:53

Ok, What kind of groud is better for

backup battery

?

VBAT (+)battery 3v (-) Vss

OR:

VBAT (+)battery 3v (-) Vssa

?

Manual told me to connect to Vss/Vssa, but i have separate grounds connected only in 1 point and i need to know what kind of ground is better for backup battery?
waclawek.jan
waclawek.jan
Super User
October 11, 2016
Posted on October 11, 2016 at 10:36

I'd say it doesn't matter - it's a low circuit current, and it's on only when the rest of circuit is powered down anyway.

JW
benny
benny
Associate III
July 11, 2018
Posted on July 11, 2018 at 22:25

I would connect the battery to Vss because the digital circuits generate noise and that should stay in the digital ground. Vssa is especially for the sensitive analog elements (as far as I know).

Kind regards

Nyix

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