STM32H747I-DISCO ground question

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

Power supply management

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mƎALLEmBest answer

ST Technical Moderator

Hello @Tycho ,

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

Two points:

According to the schematics SMPS_GND and the ground are already connected via SB9
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.

To give better visibility on the answered topics, please click "Best answer" on the reply which solved your issue or answered your question.

mƎALLEm

ST Technical Moderator

Hello,

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

To give better visibility on the answered topics, please click "Best answer" on the reply which solved your issue or answered your question.

mƎALLEmBest answer

ST Technical Moderator

Hello @Tycho ,

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

Two points:

According to the schematics SMPS_GND and the ground are already connected via SB9
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.

To give better visibility on the answered topics, please click "Best answer" on the reply which solved your issue or answered your question.

Andrew Neil

Super User

@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..

Is that information published anywhere ?

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.