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STM32H735-DK: SMPS vs LDO interesting observation



I just made an interesting observation on the STM32H735 Discovery concerning the internal core power supply.

I'm working on an ethernet bootloader for my custom board using an STM32H733, which has no internal SMPS, only the LDO.
As I do not yet have a prototype, I'm working currently with the STM32H735 Discovery Kit, which has the internal power supply wired to use its SMPS.

But here's the mistake I made when writing the bootloader code:

- I used the H733 setup using the internal LDO - and the STM32H735-DK is not wired for that

This worked for about 2 weeks without any issue, but this morning the board seemed dead, not even the STM32 programmer could access it.

After about searching for the problem I found that the firmware I made for the H735 was still working, compared the files and found my SMPS/LDO setup error, changed the bootloader accordingly, and it's working again.

I just wanted to share this interesting effect, that it worked for a few weeks with the wrong configuration, but all of a sudden it stopped.


I just checked the H7 power diagrams, and it's amazing that 

a) the H735-DK was working at all with the "direct SMPS supply" (AN5419, figure 2, config 2):

- SMPS output connected to LDO input (VDDLDO) and LDO output (VCAP), and LDO turned ON

b) that it is still working, and it seems (haven't tested everything) nothing was damaged

So, the positive conclusion: that core power part is quite robust - I like!