Min LSE Clock Speed STM32U5

[bluespider]

The table in the datasheet says that the minimum frequency for LSE in bypass mode is 5kHz (Table 71 of DS13543).
In previous designs (different STM32 MCU) I have successfully used a 125Hz input for the LSE (setting async prescaler to 1 and sync prescaler to 125), however on checking their datasheets they don’t state a minimum frequency.
I have tried running the RTC from a 125Hz source on the STM32U5A5 nucleo board that I have, and it seems to be running fine. Are there any potential problems I might encounter from doing this, as I usually try to avoid going against the datasheet!
I’m just using the LSE for the RTC, not trying to drive any other peripherals.

[AScha.3]

What is the 125hz source?

Any oscillator with low impedance output is fine, just set the RTC to LSE Bypass.

And to check for any problems with lower than DS allowed frequency test with some 10 hz or so, just to prove it will work fine with low frequency.

[STOne-32]

Dear ​@bluespider ,

 

If you are not using LSE monitoring (CSS) tamper feature, 125Hz is safe and you can have in your use case with STM32U5 for RTC.

Regards,

STOne-32.