STM32U599xxxQ LDO <-> SMPS switch

[kvrbek]

Hi all,

I'm unable to switch the internal regulator from the default LDO to the SMPS on the STM32U599NIH6Q. The function "HAL_PWREx_ConfigSupply" timeouts.
The same binary file, when flashed on the two different STM32U5 dev kits (NUCLEO-595ZJ-Q and STM32U5A9J-DK) works well (the voltage on the 2u2 capacitors changes slightly depending on the currently selected regulator).
That unfortunately does not happen on my target board(s).
The hardware design follows hardware recommendations (AN5373). Although is not excluded that there is a hardware mistake, the sample is tested on a few target boards and it fails every time.

My question is regarding the "HAL_PWREx_ConfigSupply" functions. What happens in hardware when the PWR_CR3_REGSEL bit is set/cleared and what should happen (some internal voltage reached ??) when the PWR_SVMSR_REGS reflects the selected regulator?

Attached is the demo code and SMSP-related schematics.

Regards,
Krunoslav

[Aime]

Hi @kvrbek,

The HAL_PWREx_ConfigSupply() function will change the PWR_CR3_REGSEL bit value depending on the specified regulator. Once the regulator ready the REGS will be settled/cleared accordingly. 

You can check on the VDD11 pin that the voltage level is refreshed at a different frequency depending on the regulator.
Looking on your schematic, I do not understand why do you have 3 capacitors of 100nF connected at VLXSMPS?

Please check your configuration based on the image below. It is from the datasheet and is used in the application AN5373.

Best regards,

Aime

[AScha.3]

Simply said: remove all caps from VLXSMPS .

Caps there will destroy the switch or at least stop it.

[kvrbek]

Hi @Aime, @AScha.3

Thank You for the response. Meanwhile, I had some problems with the PCB and got a replacement that worked fine and I completely forgot about it. For sure I know that there is some change in the hardware pending but cannot say at the moment if it is regarding that.
In any case, I will forward your comments to the hardware department.

Thanks, Best Regards
Krunoslav