SMPS: Necessary or Not?

[KMew]

Hello,

I am working on a custom board design and we are looking into using the STM32H7B3IIT6 or the STM32H7B3IIT6Q. The main difference I've seen between the two is the Q-version removes some of the IOs to add an SMPS.

I am trying to determine if that is necessary for my project and the documentation I'm finding doesn't really explain its necessity. It simply mentions how to use it.

My application is not ultra-low power by any means. We have a large battery bank that powers the MCU and the MCU's power consumption is VERY negligible for our application, so MCU efficiency is not mandatory.

Based on that, would that mean that we do not require SMPS? Or is there other benefits or things to consider?

[Peter BENSCH · Accepted solution]

The SMPS reduces the power loss that otherwise occurs when VDD is regulated down to the core voltage with an internal LDO. The SMPS therefore increases energy efficiency.

If you don't need to save every milliwatt, you are better off with the LDO version, also because you have more GPIOs and also one less coil and capacitor on the BOM.

Does it answer your question?

Regards

/Peter

[KMew]

Hello Peter,

Thank you for the reply! Yes, that does answer my question.

So now, I just feed the LDO and all other voltage inputs (Vref, VDDA, Vcap, Vusb, etc.) from the 3.3V power supply on my board? ​

[Peter BENSCH]

Correct, that's exactly how it is.

<edit>except VCAP, as mentioned later</edit>

Regards

/Peter

[KMew]

Hello Peter,

Thank you for confirming. Just to confirm one specific pin, since I was looking at Vcap specifically. In the specification, it has Vcap with just some capacitors and no input from the 3.3V. Does this mean that Vcap does not require the 3.3V external input?

[Tesla DeLorean]

VCAP connects to the internal LDO, which in use outputs about 1.25V