STM32U073CCT6 ELSE disturbed By RF Field

[gilberto-falker]

Hi

We are using an STM32U073CCT6 as a host controller in a LoRaWAN device. We recently modified our design to incorporate an LSE (Low-Speed ​​External) oscillator to improve the precision of the RTC.

The LSE is functional, but it occasionally stops oscillating when the LoRaWAN module transmits a message. We have already checked the power supply, ground, and all associated components, but the issue persists. Is it possible that the STM32U0 is experiencing internal interference—perhaps through demodulation by its protection diodes—caused by the LoRaWAN transmission? The LSE remains stalled for the entire duration that the RF signal is active.

BR

Gilberto

PS. I can not edit the title. Please correct it.

[Ozone]

I’m not a hardware guy or PCB design expert, but I suspect either PCB-releated EMI issues or coupling due to physical proximity.

If you e.g. look closer at singleboard Linux computers like the Raspberry Pi, you will find the Wireless/BT modules are shielded.
I suppose for good reasons.

[gbm]

There are few similar topics on this forum - search for them. PCB design details are VERY important for LSE. A s quick solution, you may try to set “drive strength” option in LSE config (if it is available in your MCU) - sometimes that might be enough. Generally - no ground plane unde LSE and its signal traces, keep them as short as possible and no other signal traces close to them/crossing them in other planes.