What's the Correct Power Supply Scheme for H725/735 VFQFPN68 Package?

[Leonana69]

Since the VFQFPN68 package doesn't provide the VDDLDO, should the chip work just with VDD/VBAT/VDDA all connected to 3v3?

Updates: during my unit test, I kept only the STM32H725 chip on the board and removed all the other components. Then I powered the chip with 3v3 to VDD/VBAT/VDDA, but the VCAP was around 100mv and I couldn't connect to the chip. However, once I supplied 1v2 to VCAP, I could connect to it. I wonder what could cause the problem, I though the chip should have an internal LDO to power the Core.

[Amel NASRI]

Hi @Leonana69 ,

As explained in AN5419 Getting started with STM32H723/733, STM32H725/735 and STM32H730 Value
Line hardware development, "When it is not available on an external pin, VDDLDO is connected internally to VDD."

In the same document, please refer to the figure "System supply configuration" and the table "Power supply connection" to know more about required setup for VCAP.

-Amel

[jmarino]

I don't understand why are the SMPS pins available since it can't be used to power the LDO.

Is there any way to power the MCU using the SMPS?

[KDJEM.1]

Hello @jmarino ,

If I have understood your comment correctly, you are asking how to connect SMPS when no available VDDLDO like as STM32H725  VFQFPN68 package.

According to AN5419 the connection for VQFPN68 package should be like shown in the figure below

If I haven't understood your comment or you need further clarification please create a dedicate thread for your request.

Thank you.

Kaouthar  

[jmarino]

Thank you very much for your answer, but:

- Where in AN5419 is that schematic? It doesn't match with any of system supply configurations in Figure 2 (page 6).

- In page 12, inside "2.1.6 LDO voltage regulator", it says that "When it is not available on an external pin, VDDLDO
is connected internally to VDD", but it doesn't says anything about having VCAP tied to VFBSMPS.

- If that internal connection between VCAP and VFBSMPS that is shown in your schematic is true, how must I disable the use of SMPS, since their pins can't be tied to ground as stated in the document?.

Regards,

[jmarino]

Well, I made a mistake and the connection between VCAP and VFBSMP in your schematic is not internal, but external, so forget the last question.

But I still need to know if it's OK to connect VCAP and VFBSMP while VDDLDO is internally connected to VDD. In AN5419, the way of bypassing LDO is always connecting VDDLDO to VCAP, and you're proposing to give power to VCAP through SMPS while LDO is on (VDDLDO internally connected to VDD).

[jmarino]

I read more documents once and once again, and I think that the documents are not clear enough.

In the Reference Manual, in page 232, it says:

"When LDO is available but VDDLDO pin is not present on the package, VDDLDO is internally connected to

VDD."

But, in the Datasheet, in page 1, it says:

"Embedded DCDC and LDO regulator

(*)VFQFPN68 variant is DCDC only"

The fact is that VFQFPN68 package is the only one that doesn't have a VDDLDO pin, and the Reference Manual statement confused me, making me to think that there was an LDO with its input connected to VDD. But it seems that there isn't any LDO at all, right?