USB OTG_HS_VBUS on STM32H series

[steve_edwards]

Hi,

I have a question about whether or not the USB VBUS connection needs to be made to the micro on the STM32H series micros (in particular the STM32H725) when operating the USB in device mode.

We are using a USB-C type connection, so we have an independent IC which performs OTG host/device detection based on the USB-C VBUS and CC1, CC2 USB-C pins, but it is not clear whether we also need to connect the VBUS to the micro's OTG_HS_VBUS pin  (PA9 on this micro) to start the comms sequence when the micro is a device.

On previous STM32F series micros I believe it was mandatory to make this connection because it powered the USB transceiver but I'm not sure that this is still the case on the STM32H micros, or whether the new USB regulator can somehow be used to perform this instead (or is that just for host mode)?

Thanks for any help you can give with this.

Steve

[FBL]

Hi @steve_edwards & welcome to ST Community

Well, it depends on your application. Bus-powered application doesn’t need VBUS sensing. It's possible to monirtor VBUS but it is not mandatory. On self-powered devices, VBUS sensing is mandatory. See this Management of VBUS sensing for USB device design - STMicroelectronics Community

[steve_edwards]

Hi @FBL 

Thanks your quick response.

So we have a self-powered device therefore it seems VBUS sensing is mandatory, however we can already sense this via our independent IC (we communicate with it over I2C). However, I guess that would mean that we would have to find the location in the USB driver where it monitors PA9 (the official VBUS pin) and make suitable changes.

So instead, it may be much easier just to make the connection to PA9. The link you provided also contains information about the 5V tolerance limitation with this pin on STM32F7 devices (where they are only 4V tolerant in the event the micro is not powered). Can you confirm whether this is still an issue for the STM32H725 device that we are now using? Because although we will be a self-powered device, there is still a possible use case where a USB lead would be connected while the device is powered-off.

Thanks,

Steve