STM32H745 VDDSMPS Default Configuration?

[NLuon.3]

Hello,

I have 2 clarification questions on the default VDDSMPS configuration for the STM32H745:

1. I notice multiple times in the STM32H745xI/G datasheet that "VDDSMPS must be kept the same voltage level as VDD." Similarly, RM0399 also has a note that VDDSMPS shall be connected to VDD. I also see in RM0399, Figure 22 that there are multiple system supply configurations where VDDSMPS is connected to GND. Are those valid configurations, or should VDDSMPS be connected to VDD?
2. If I understand the datasheet correctly, the Default Supply configuration (outlined in RM0399 Table 32) should use the LDO Supply configuration (outlined in RM0399 Figure 22 with VDDSMPS connected to GND). Can someone please confirm this understanding is correct?

Thanks,

Nicholas

[SofLit]

Dear @NLuon.3​ ,

1- VDDSMPS must be tied to VDD only when SMPS is used. If you look at the different configurations in figure 22, you will find that VDDSMPS is connected to VDD only if SMPS is used, otherwise it will be tied to the ground.

I will request to change the note at page 272 in order to be more clear about this connection.

2- The MCU boots up from the default configuration and power configuration will switch to what user defined in his software in PWR_CR3 register.

If you refer to RM0399 rev 3 / "7.4.1 System supply startup" you find the different power configurations start-up:

• Figure 23. Device startup with VCORE supplied from voltage regulator
• Figure 24. Device startup with VCORE supplied directly from SMPS step-down converter
• Figure 25. Device startup with VCORE supplied in Bypass mode from external regulator

The different steps are described at the beginning of the section 7.4.1.

Each figure shows the "Default configuration" phase and the switch to the user power config phase..

 

If I answered your question, please mark this topic as answered by selecting Select as best. This will help other users find that answer faster. For follow-up question I suggest to open a new thread.

[Amel NASRI]

+ to @Community member​'s answer: you can refer to the article Unable to connect to STM32H7 devices which contains some explanations in its first part.

-Amel

[SofLit]

Hi,

In RM0399 / section "7.4 Power supplies" and after the phrase "VDDSMPS external power supply for step-down converter" the following statement has been added: "This power supply shall be connected to VDD when SMPS is used. Otherwise, it must be connected to GND" in internal revision of the document. The new revision 4 will be available soon on ST website.