STM32F429IET6 RTC power off/on issue

[ALee.13]

We are suing STM32F429IET6 in our project. The schematics as follow:

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1. if VBAT=2.2~3.6V :backhand_index_pointing_right: :backhand_index_pointing_right: :backhand_index_pointing_right: Power off the VDD and wait 0~180 seconds, then power on again. The RTC always lost(reset to the begin value).
2. if VBAT=1.6~2.0V :backhand_index_pointing_right: :backhand_index_pointing_right: :backhand_index_pointing_right: Power off the VDD and wait 20~180 seconds, then power on. The RTC work fine.
3. if VBAT=1.6~2.0V :backhand_index_pointing_right: :backhand_index_pointing_right: :backhand_index_pointing_right: Power off the VDD and wait 2~15 seconds, then power on. Sometime, the RTC lost(reset to the begin value).

RTC lost value when VBAT > 2.2V.

How to resolve the issue? Do you have any recommend?

Best Regards,

Aaron

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[TFung]

It does not make sense at higher voltage VBAT (within range) cause the RTC to reset to default value.

May be it is something else, like power surge or something ?

[ALee.13]

Hi,

We found the BYPASS_REG is floating.

We connect it to GND can resolve that issue.

Best Regards,

Aaron