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Associate II


I have a numberd of assembed PCBs (120pcs) based on STM32WLE5CCU6 with HP LoRa in lowband (433Mhz).

Everythigs would be fine, except the trouble: about 20% of ready made PCBs are not working. During my investigation I discovered that MCU just unable to communicate with its radio part via SPI. The error I've got is HAL_SUBGHZ_ERROR_TIMEOUT at the very first call to radio. While the same code is working fine on the majority of the same board.

So I started to explore what could go wrong and found that mysterious pin VDDPA. There is no clearly stated voltage ratings of this pin anywhere in DS or RM.

My board works with VDD=3.6V, and this voltage is applied to VDDPA, as the docs said that this should be VDD to reach maximum power. But Table 19 in the RM makes me confused as all it shows is only up to 3.3V. I've searched through the web and found out a couple of derivative devices based on STM32WLE5 which datasheets states VDDPA maximum is 3.6V. This is encouraging, but...

So my questions is:

* What is the voltage rating of VDDPA?

* Could 3.6V on VDDPA be the root issue for destruction of about 20% of MCUs?

* May there be other reasons?