STM32H7R3. SMPS and VCORE.

[Pawel Piwowarski]

Hello

Can anybody explain how it is possible to power VCORE directly from SMPS output?

I see that SMPS have only two possible output voltages, 1.8V and 2.5V:

But VCORE accepts absolute maximum of 1.4V.

So how it is possible with LDO bypassed?

Best Regards

[ELABI.1 · Accepted solution]

Hi @Pawel Piwowarski 

Depending on the mode you wish to work in,

you need to properly set the bits (SDHILEVEL, SMPSEXTHP, SDEN, LDOEN, BYPASS) found in Table 44. Supply Configuration Control in the Reference Manual RM0477

For the SDHILEVEL bit, which controls whether the SMPS outputs 1.8V or 1.2V

• If this bit is set to 0 -> 1.2V
• If it is set to 1 -> 1.8V

Thank you.

ELABI.1

[Pawel Piwowarski]

Thanks.

So there are two additional information, important for me:

1. SMPS may have different voltage than 1.8 / 2.5 V.

2. There are another power mode, not indicated in schematic: SMPS on, VCORE powered from SMPS but with LDO on.

Thanks for this.

Best regards.

[ELABI.1]

Hi @Pawel Piwowarski,

When the LDO is on, it only powers the Vcore. You cannot power the Vcore with both the SMPS and the LDO at the same time.

Thanks.

ELABI.1

[Pawel Piwowarski]

I mean the situation when VCORE is powered from SMPS thru LDO.

This mode is not listed here:

But it was mentioned here:

The closest mode is mode 3, when we externally make this connection:

But for some reason, You didn't include this mode in the documentation.

[tdecker2]

Does someone has more information on this usecase? CubeMX also allows this mode on a H7R/S controller: SupplySource can be set to PWR_SMPS_1V8_SUPPLIES_LDO or PWR_SMPS_1V8_SUPPLIES_EXT_AND_LDO.

I've also seen this mode in reference manuals of other controller families, but as @Pawel Piwowarski already mentioned, it is missing in the Power supply management chapter of the RM.

Two more questions coming up to this configuration:

• Does the integrated bootloader also support this?
• I assume, I can power my xSPI peripheral and external RAM/Flash with the 1.8V of the SMPS this way (using option PWR_SMPS_1V8_SUPPLIES_EXT_AND_LDO)?

[ELABI.1]

Hi @Pawel Piwowarski,

For this mode in the STM32H7RS, it's not supported. Therefore, the phrase mentioned in Table 44: "SMPS step-down converter enabled at 1.35 V, may be used to supply the LDO" will be updated in the next release.

Note: You need to update your datasheet document because I noticed there is a difference between Table 28 SMPS step-down converter characteristics for external usage which exists on the website and your version.

Your screenshot:

Which exists on the website:

Thank you.

ELABI.1