STM32H747I-DISCO ground question

[Tycho]

On STM32H747I-DISCO schematic, there are two different grounds. Why is SMPS ground connected to B6, C16 and T12?

[mƎALLEm]

Hello,

I'm checking internally and I'll get back to you if I have an answer.

[mƎALLEm]

Hello @Tycho ,

I'm getting back to you even after a while (receiving a feedback recently from experts) regarding this topic.

Two points:

1. According to the schematics SMPS_GND and the ground are already connected via SB9
2. According to the board designer the three VSS balls are internally close to some VDDIO33_LDO pins, and consequently, must be connected to SMPS_GND and not VSS as usually, for better signal immunity of LDO and he recommends to follow this rule in your design.

Hope I answered your question.

[Andrew Neil]

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@mƎALLEm wrote:

2. According to the board designer the three VSS balls are internally close to some VDDIO33_LDO pins, and consequently, must be connected to SMPS_GND and not VSS as usually, for better signal immunity of LDO and he recommends to follow this rule in your design..

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Is that information published anywhere ?

[mƎALLEm]

I don't think so.. could be a note to be added in the AN4938: https://www.st.com/resource/en/application_note/an4938-getting-started-with-stm32h74xig-and-stm32h75xig-mcu-hardware-development-stmicroelectronics.pdf