RTC stops at high temperature with LSE clock sourced from a crystal oscillator

[Red_Mask]

Hello!
I am using a 32.768 kHz TCXO (TG-3541CE) as the LSE to count the RTC.
The MCU is an STM32L452RE.
At room temperature, the RTC operates correctly, but at high temperatures (around 50 °C), the RTC stops.
Strangely, once it has stopped, touching the MCU by finger causes the RTC to start running again.
Suspecting an issue with the TCXO, I tried a different TCXO, but the same behavior occurred.

When I added a 200 Ω damping resistor between the TCXO and the MCU, the RTC no longer stopped even when the temperature was raised to 60 °C.
This seems to have solved the problem for now, but I am concerned about whether 200 Ω is an appropriate value and whether this is truly a fundamental solution.
If you have any ideas about possible root causes or considerations, I would really appreciate your advice.

[Red_Mask]

Thank you for your response!

I would appreciate it if you could let me know if there are any precautions to take regarding the STM32 LSE drive configuration.
Also, regarding the open link — I can’t seem to access the discussion page when I click it. Could you please send me the link again?

[waclawek.jan · Accepted solution]

You may have replied to a spammer - these days they regurgitate the thread through AI to have them look legit, and try to inject a fradulent link. That post has been manually reviewed and removed.

As you use an external TCXO, LSE drive strength should be irrelevant (AI-generated text will mention it as a LLM is trained to infer that from "LSE problems".)

At this point there's probably not much the public forum here can do to help you. You may want to contact ST directly, through FAE or the web support form.

JW

[Red_Mask]

Thank you so much!

I will contact ST directly.