RTC of the STM32F745 works inaccurate

[HSchm.1]

I am using the RTC of the STM32F745 with 32.768kHz LSE.

Principially, the RTC work correct on several PCBs.

But there is one PCB where the RTC goes approx. 7 Min too slow in one hour.

But if the unit is powered of and the RTC works with VBat for a while, it goes correct, if I control it after power on again.

Has someone a clue, where to search the failure?

[waclawek.jan]

> But there is one PCB where the RTC goes approx. 7 Min too slow in one hour.

So, is the RTC late only if it runs out of VDD, i.e. not out of VBAT?

Do you reset the board during this time? (I am aiming at the "Cube initializes RTC upon every reset, leading to half-second-per-reset "time loss" in average" Cube bug).

If not, can't this be result of excessive noise in the analog supply (VDDA), potentially throwing off the low-power oscillator? Try changing the oscillator drive strength, if it's possible in this model of STM32.

JW

[HSchm.1]

Thanks for the tips.

I have changed the drive strenght to high, and it seems to work now.

Heiko