[solved] STM32H725 SMPS issue

[ubbut]

Solved: Is a STM32Cube bug:
https://community.st.com/t5/stm32cubeide-mcus/default-settings-for-nucleo-h755-not-working-after-power-off/m-p/760162

I am having and issue with a STM32H725RGV6.

After powering my board, I can see the SMPS output at 1.36V, which I have connected to the VCAP inputs.
I can also connect to the µC using the STM32CubeProgrammer.

However, after flashing a simple firmware, the SMSP output drops to 0V and I can not connect anymore. I am aware that this can be the result of an improper SMPS configuration (https://community.st.com/t5/stm32-mcus/unable-to-connect-to-stm32h7-devices/ta-p/49296). However, in my (cube generated) project am am calling

HAL_PWREx_ConfigSupply(PWR_DIRECT_SMPS_SUPPLY)

so this should be correct. Additionally, I tried to upload a program with nothing but an infinite loop in main, and the problem still occurs.

When pulling BOOT0 high, the SMSP output becomes 1.36V again and I can connect again. This makes me believe, that everything is set-up correctly hardware-wise. Otherwise, the bootloader would not run. 

This package does not have the LDO option by the way, otherwise I would just use that.

thank you for your help

[SiliconWizard]

I didn't know that some variants of the STM32H7 didn't have an internal LDO. That's interesting.

[hans]

Well all parts have the LDO, but not all parts have the VDDLDO pin exposed.

Basically the switcher can be used to either supply VDDLDO, VCAP, and/or something external. Smaller packages don't have VDDLDO, so the only way to use it as a power saving feature for the internal core is to directly supply VCAP.
But you could also have the SMPS  supply the LDO, and have the intermediate voltage set at 1.8 or 2.5V to supply something external. Or, just wire VDDLDO to VDD, and then use the SMPS completely separate. Maybe for some applications the space/cost saving of a trading dedicated switcher with the MCU's internal one is a neat feature.