Do GPIO shared with USB need the "USB block" power requirements?

[md5]

Hello,

We have made a devboard with stm32h7s3, running at VDD = 1.8V.

We are finding that a number of pins shared with the USBHS/FS peripheral (which we are using as simple GPIO) do not work properly, ie. cannot be used for digital output.

This is for select pins on Port M - you can ctrl+F the datasheet for "FT_u" to find them. They seem to be pulled low though a resistor a little weaker than 10k.

 

There is a note on page 581 of the reference manual that says

"GPIOs that are shared with the USB are limited in terms of frequency, to hundreds of kHz for UCPD-based GPIOs, and up to 1 MHz for USBHS and USBFS-based GPIOs. Refer to the datsheet for the exact values. In order to be used the IO supply must be above 2.7 V for the USBHS/FS."

Our initial read was that this applied to using the USB peripheral, but our findings now suggest that a >2.7V supply is required just to use the pins as GPIO? We have DVDD, VDD50USB, and VDD33USB to 0V since we thought this was only for the USB peripheral.

Could someone confirm that this is the case?

If true, we feel that paragraph could be worded a lot more clearly. If not, we are very curious if there are any suggestions for why this might be happening.

 

Thanks!

 

Reference manual link: STM32H7Rx/7Sx Arm<Sup>®</Sup>-based 32-bit MCUs - Reference manual

Datasheet link: Datasheet - STM32H7Sxx8 - Arm<Sup>®</Sup> Cortex<Sup>®</Sup>-M7 32-bit 600 MHz MCU, 64 KB flash, 620 KB RAM, Ethernet, 2x USB, 2x FD-CAN, advanced graphics and security, 2x12-bit ADCs

[TDK]

Which pins exactly?

 

It is recommended that VDD50USB and VDD33USB be tied to VDD when USB is not used in a few places, but without any rationale. DVDD should be grounded per the datasheet.

 

There is a mention of the chip behavior not being guaranteed if VDD50USB is floating.

FAQ: Configuring the VDD50USB and VDD33USB pins on... - STMicroelectronics Community

 

[md5]

In the reference manual it really suggests VDD50USB and VDD33USB are for USB - I mean look at the names. It might work if we connect these to VDD (currently GND), but we can't know until a new board rev - can't exactly solder a wire to BGA.

 

The pins in question are PM3, PM5 and PM6. Perhaps others are affected too, but these are the ones we have fought with.

 

Any other pointers that might make this work without a new board spin?

[TDK]

They are definitely used for USB, but protection diodes within the device may make the precise plumbing more complicated. I don't have details here, just going off of application notes and experience.

Can't find a reason in the datasheet why these would be pulled down, but that's my best guess. It's unfortunate that it requires a re-spin to test that theory.

 

> Any other pointers that might make this work without a new board spin?

Did you look at changing the relevant PWR_UCPDR registers per the footnote I showed above? Doubt that's it but that's all I got.

[md5]

Hi there,

After consulting with our hardware guy, he pointed out that the app note referenced in the guide you posted is for a different subfamily than what we use.

The app note for the family we use (stm32h7s3) says explicitly that VDD33USB should be 0V for supply 0-3.6V.

See page 9.

Getting started with STM32H7Rx/7Sx MCUs hardware development - Application note

 

[FBL]

Hi @md5 

Did you enable HSLV ?

For STM32H7S3, checking section 6.8.4 PWR control register 2 (PWR_CSR2)

So, we confirm that all GPIO port M is in USB power domain and it’s necessary to supply them if any GPIO port M is used.
So in your case when USB is not used :
-VDD50USB have to be connected to VDD33USB,
-VDD33USB is supplied by 3.3 V,
-the internal regulator USB shall be disactivated (reset value).

[md5]

Hi there,

HSLV is enabled.

Thanks for getting back with the confirmation. We will change this in the next board rev.

I wish this was a little more clear in the documentation! We really did try to be quite thorough and managed to come to the wrong conclusion with the document that we got out hands on.

Your time is appreciated.