STM32H745 - unused SMPS pins

[Joe.H]

I don't use the internal Step Down regulator. How should the pins be tied?

Should VDDSMPS be tied to VDD and VSSSMPS to GND with VLXSMPS and VFBSMPS left open?

OR - should they ALL be left open?

Documentation only speaks as if they are to be used - no comments on what to do if not used.

[TDK · Accepted solution]

This app note for STM32H7A/B shows them as grounded/floating. Can't imagine it's different for the H745.

 

 

https://www.st.com/resource/en/application_note/an5307-getting-started-with-stm32h7a37b3-line-and-stm32h7b0-value-line-microcontroller-hardware-development-stmicroelectronics.pdf

[Joe.H]

Thanks

[Moritz_]

Hi,

is the same solution possible for the STM32H747XIH6?

I want to fully bypass the internal LDO and SMPS.

Thank you-

[mƎALLEm]

 STM32H747 and STM32H745 have the same config from power settings point of view.

[Moritz_]

Thank you very much for the fast help.

[Moritz_]

Just to be sure, (since the datasheet of the STM32H747 does not mention it) VDDLDO and VCAP are connected in the LDO bypass scenario ?

[sndafrei]

Hi WARNING I think.
The Voltage must be the same as the voltage you used for VDD!!!

I burned a uC because I used this information :)

Good luck!

Daniel

[mƎALLEm]

"The Voltage must be the same as the voltage you used for VDD" is for SMPS configuration.

VDDSMPS should be connected to the ground if LDO mode is used. 

You may burned your chip for another reason.

[sndafrei]

Hi, thank you for your fast reply.
I used the STM32H735ZG and wired it in this way:

I powered the PCB and try to reach the uC with the programmer.
I reached the uC with STM Cube Programmer and read out the serial several times and it works.

Then I bring the PCB to my customer and he NOT powered the PCB itself he only connects an programmer ST Link V2. Over this programmer he connect the 3.3V to the PCB.
He has also reached the uC successfully and successfully upload a program.
After the upload he can't reach the uC a second time.

I investigate it and figure out, that there is 0V at the VCAP.
I changed the VDDSMPS to 3.3V and disconnect the VFBSMPS from GND.
I also changed the Pull-Up resistor at PDR_ON to 0R and removed the resistor at VBAT (VBAT now floating).
Then I also removed the connection from VDD50USB (VDD50USB now floating).

After I have done all this the VCAP was still at 0V and I think this uC is dead.

What do you think what could happened here?
Is the SMPS wiring correct as I have done it?

I only want to have 3.3V at the uC from my LDO at the PCB. I not want to use any on these SMPS function.

Is there something the customer can configure wrong in the CubeMX/ CubeIDE to destroy the uC because of the actual wiring?

Thank you for your reply :)