Stuck in RCC_FLAG_LSERDY after bootup when VBAT is present

[devjeetmandal09]

PART NO: STM32H743IIT6
CUBE_IDE VER: 1.19.0
SDK : STM32Cube FW_H7 V1.12.1
LSE PART NO. : CM9V-T1A-32.768kHz-12.5pF-20PPM-TA-QC


Hello everyone,
I am trying to use RTC on mentioned STM part number. I have enable LSE and configured the RTC.
Currently i am not using any battery, i am using a power supply with 3V to VBAT.

After boot up inside HAL_RCC_OscConfig, i am getting timeout while checking RCC_FLAG_LSERDY flag.

while (__HAL_RCC_GET_FLAG(RCC_FLAG_LSERDY) == 0U)
 {
    if ((HAL_GetTick() - tickstart) > RCC_LSE_TIMEOUT_VALUE)
    {
       return HAL_TIMEOUT;
    }
 }

The sequence is, once i have provided VDD then VBAT, everything works fine.
Next i just turn off the VDD, VBAT is still present.
Then i turn on the VDD and facing this issue.

Another thing to note is, i am not facing this issue with LSI. So i changed the crystal but facing the same issue.

Also the PDR_ON pin is connected to VDD according to specifications.

Is it possible to provide any insight of why this is happening? and how to resolve this?
Any feedback will be appreciated.

Best Regards,
Devjeet Mandal

[devjeetmandal09]

Hello everyone,
Is there any comment regarding this?

Thanks

[mƎALLEm]

Hello,

Probably it's due to your crystal that could be not compatible with the STM32 LSE or you didn't set the correct drive level that allows the oscillator to start.

I invite you to read the article: How to select a compatible crystal and load capacitors for STM32 with layout guidelines

Or more details can be found in the AN2867 "Guidelines for oscillator design on STM8AF/AL/S and STM32 MCUs/MPUs". Section 6 provides some recommended crystals for each MCU family.