What's the Correct Power Supply Scheme for STM32H725RGV6 VFQFPN68 Package

[Hary]

Hi Experts,

I am facing an issue with my custom board based on the STM32H725RGV6. The VCAP voltage remains around 80 mV, preventing the MCU from starting.

My intention is not to use the internal SMPS, and I would like to operate the controller in the 100-200 MHz range using the external LDO regulator (As internal LDO not available)

Could you please help clarify the following:

• Can the VFQFPN68 package operate using the internal LDO only, without the SMPS circuitry?
• Is a VCAP voltage of approximately 80 mV indicative of an incorrect power configuration, damaged device, or missing connection?
• If the internal LDO is unavailable in this package, would supplying a stable external 1.2 V rail to the VCAP pins while keeping the SMPS disabled/bypassed be a valid solution?
• Or is the use of the SMPS pins and associated external components mandatory for this device/package?

Unfortunately, my PCB layout does not have sufficient space remaining to accommodate the SMPS inductor and related components, so I am looking for the most practical solution without a board re-spin if possible.

Please suggest the recommended approach and confirm the best solution for this configuration.

Here is schematics of the MCU section:

 

 

Thanks in advance for your support.

Best regards,
Harinder Singh

[Andrew Neil]

What does the datasheet have to say ?

Have you studied Application note AN5935, Getting started with STM32H7Rx/7Sx MCUs hardware development ?

 

Presentation on the STM32H7 power controller

[Hary]

Hi,

Datasheet say’s SMT32h725rgv6 package has only DCDC option.

I want to use this arrangement, Is it safe to connect 1.2V from External LDO if fixed output & 300mA rating while keeping the SMPS connections connected to ground as shown in the picture?

 

[mƎALLEm]

Hello ​@Hary and welcome to the ST community,

The answer is yes if you follow the exact hardware schematic specified in 6. Bypass. and keep the Vcap voltage > 1.1V.

Please refer to the RM0468  / paragraph: VCORE supplied in Bypass mode (LDO and SMPS OFF):

Hope that helps.

[George Wu]

Hi ​@Hary 

Here is expected solution.

 

[Hary]

In some STM32H7 part specially WFQFPN68 doesn’t have VDDLDO pin, so this arrangement will not work. ST has given two options for this package:
1. Use Internal SMPS arrangement to drive Vcap voltage. (*Option is not feasible in my case as there is space issue)
2. Bypass SMSPS and Use external LDO of 1.2V on the Vcap pins.