RTC not working on STM32L073RZ

[UShah.15]

We have made 500 PCB's with STM32L073RZ and 150 have issue in starting the RTC.

We have used the recommended 32.768Khz but its not working for the 150.

We have tried changing the recommended 32.768Khz with the cylindrical crystal it worked but when I tested after an hour it was not working.

If I heat the RTC with the blower it works and later it stops working. It works when we touch on the PCB with hands touched on the crystal and its caps.

I have tested changing the crystal its 4.3pF caps but not working.

I have soldered the 8Mhz crystal body to ground, changed the LSE crystal with cylindrical crystal and grounded it body but it works temporarily and later stops working.

I have been programming the PCB with mbed OS and everytime it shows "Cannot initialize RTC with LSE" error.

The PCB layout is also attached.

Please guide.

[UShah.15]

Hello,

Need help to solve this issue

Any guidance will be appreciated.

[waclawek.jan]

Have you tried tweaking RCC_CSR.LSEDRV?

JW

[UShah.15]

Thanks for your suggestion, we tried tweaking RCC_CSR.LSEDRV changing the power to different levels but it didn't help.

Any other suggestion please.

Thank you.

[waclawek.jan]

Try to run the same code on a "known good" board such as a Nucleo or Disco with a similar STM32. This should reveal whether you do something wrong in code, or the problem is indeed in hardware.

Review AN2867.

JW