STM32G0B1X RTC_OUTPUT generated at ADC_IN pin number PA4

[st21]

Hi team,

I am using STM32G0B1 for my project development were I use PA4 as a ADC_IN in analog mode and using RTC for date and time setting, though I am not using(/set) RTC_OUT but  1 Hz RTC calibration output getting activated at power on or at rebbot. 

To fix this issue I explicitly calling the “HAL_RTCEx_DeactivateCalibrationOutPut(&hrtc)” in main.c this fix the issue.

What is the expected fix of this issue? why its occuring ? does the place/time of calling that API matters?

[waclawek.jan]

Sound like consequence of the backup domain brownout erratum.

How is VBAT powered?

JW

[st21]

VBAT is powered by a lithium 3v coin battery.

[st21]

I forget to mention that RTC out calibration is activated at power on or at reboot on PA4 pin which I am using as a ADC_IN. 

[waclawek.jan]

What is the voltage on VBAT pin, as measured directly at the pin, when the board is powered down?

JW

[st21]

We dont use any battery to this board , rtc will updated by master board after power on.

[waclawek.jan]

And VBAT is connected to VDD as recommended, then?

At any case, you want to perform a backup-domain reset (see RCC_BDCR.BDRST) just after the system reset, before setting up RTC and its clock.

JW

[st21]

VBAT is connectec to VDD and  Backup-domain reset (RCC_BDCR.BDRST) is not used in this scenario.

[waclawek.jan]

Well, then use it.

JW