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Time taken to switch to VBAT from VDD by RTC for STM32F091VCT6

jhalife
Associate

‎2025-07-11 6:57 AM - last edited on ‎2025-07-11 7:03 AM by

Hi,

We are using STM32F091VCT6 in our application, however we are observing some instance of RTC losing time. We checked entire datasheet but were unable to figure out how much time the RTC takes to switch to VBAT after VDD falls below given threshold? Can you help us with the specification to rule out any issue related to timing here? In our case VBAT goes to a series diode and is than connected to the controller.

 

Any more insight would be helpful

jhalife_1-1752242174679.png

 

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waclawek.jan
Super User

‎2025-07-11 7:42 AM

If there's a real battery with sufficient voltage connected to VBAT, loss of VDD should not result in loss of time.  

> we are observing some instance of RTC losing time

Describe circumstances when this happens. What are you observing exactly, and how? How are you setting/resetting RTC and what are you doing at startup with the backup domain?

JW 

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