STM32H745 EMC Behaviour internal Power

[JPiet.3]

Hello,

I look for information, what is the best layout for the SMPS, which is included in the STM32H745. One of my problems is, for a proper design, you must consider to have small loops in the switching path.

For my base layout, I used the same structure as it is used on the eval-kit. When I now look at the processor datasheet, I see no dedicated pins for ground, assigned to the SMPS. Where it is described to use the 3 ground pins (C16, T12, B6 on STM32H745XIH6) in this kind (Eval Kit MB1381)? These selected pins are on the opposite from the regulator. From EMC point of view, it is not really the best configuration. VSSSMPS(Pin-F2) is on the correct place, but the layout in the eval-kit is also not the best (with respect to emc) but with the three pins above, a proper groundplane underneath the processor is not possible.

If someone has some documents , application notes or practical hints, I would be happy if you can share these information. My circuit, derived from the evalkit, you can see in the attached image.

Thanks,

Jan

[CYANG.1 · Accepted solution]

Hi,

The 3 ground pins are close VCAP, which would be loader of the power from SMPS output. 

So you may treat this ground panel as ground of output as normal DCDC circuit.

B.R.

[JPiet.3]

HI,

it is acceptable, what you say. Unfortunatelly, it is not recognizable to see this in the datasheet. All pins are named as GND. I see with " VSSSMPS" just one dedicated ground, which is for the SMPS.

I got the information just from the Nucleo Eval-Kit but even here, from outside view, these 3 pins are just in whole GND-connection visible.

A different naming for pinout for these pins in datasheet would be very helpful for the developer.

Jan