STM32F765 RTC error 2 seconds per day.

[YS_Dev]

Hello, I have some project with RTC. Initially project was made with STM32F405 uC, now all porting to STM32F765 uC. Problem with RTC, on the new board with F7 uC I have error around 2 sec per day, where board f405 - I have error 1 sec in 4-5 days. Both boards working from external 32768 crystal (part number is same, caps are same 12 pf), power present all time. Can someone explain how I can detect the problem?  

[waclawek.jan]

The LSE oscillator is an extremely low-power circuit. Different layout, different signals/ground routing, different power supply, different signals surrounding/coupling to LSE, different internal LSE circuitry - this all may play some role in the observed difference (which is around 20ppm).

Is the frequency/deviation stable? Try changing the capacitors. You can also try to experiment with different LSEDRV settings.

JW