STM32H7 Custom Project prototype , power issues

[pema]

Hi there,

this is my first post here. So be gentle with me 😉

I been working on a project with STM32H757XIH6 for some time now, but without any success. This is already my 2nd prototype and costed me quite some $$ since it had to be a 8 layer PCB. The soldering I have performed my self with a heat gun and heating platform...This worked fine in the past.

I checked everything already several times, but since I am doing this one alone, I most have missed something.

The issue has to be from the MCU connection/Layout since this one gets super hot when I power the board. If I desolder the MCU out, I can control the other devices(power supplies I2C devices, SPI, etc ).

The power input looks like this:

From the System supply configurations I intend to use this one (in red). Being SMPS off and Vreg on.

Am I missing something ?The 3.3V  are stable when I desolder the MCU.

I would appreciate any help since I am quite stuck on this issue alone .

Much appreciated in advance.

[TDK · Accepted solution]

VCAPDSI should not be connected to VDD. It should be bypassed to GND with a 2.2uF cap.

Technically, VCAP pins should be tied together, but unlikely this will cause any issues.

[tjaekel]

It looks to me: you use a chip with SMPS, but you try to wire like only using LDO.

I am not sure if this works: VDDSMPS and VFBSMSP wired to GND and assuming SMPS is off by default - which I would not take as granted.

Based on my datasheet studies: you have to decide to go with a SMPS chip or an LDO chip. Different pinout on MCU chip!.

Even there is an LDO when you go with SMPS - the LDO is after the SMPS!

So, for a package with SMPS - I wire SMPS correctly (with the inductor). I can enable LDO afterwards, after MCU is running.

So, my five cents: your chip is an SMPS chip, but your SMPS wiring is not correct (where does the figure 22 come from?). Chip starts in SMPS mode (but does not find the external inductor).

If you want to go with LDO only - use a package intended for LDO only.

[pema]

Hi @TDK , yes you are right ...I assume I could try by leaving it floating for the moment. Since these BGAs are very tricky to "remove pins".

to solder.

Thank you very much !

[pema]

Hi @tjaekel ,

yes you are correct my chip as SMPS and yes I am trying to connect it without the SMPS and just LDO active.

According to the reference manual this should be possible. Yes I should have chose a package without SMPS, but when I started working on this project this was the only package with MIPI-DSI. And I assumed that since the user manual says you can leave it disabled then its okay.

The figure 22 comes from the reference manual page 274/3556 (link below).

https://www.st.com/resource/en/reference_manual/rm0399-stm32h745755-and-stm32h747757-advanced-armbased-32bit-mcus-stmicroelectronics.pdf

Its also found this the. Which confirms what I assumed from the beginning...am I missing any detail ?