STM32F723 HS and FS ID \ VBUS pin usages.

[Bags]

 

Currently designing a PCB that has a USB-C 16 pin connector. For maximum flexibility the PCB can take either a H723 or a F723 MCU. (The H723 has USB FS pins only, whereas the F723 also has USB HS pins available). This design allows it to operate in either USB in FS or HS modes but with only a single USB C port.

1 - What is best practice for wiring up the STM32 USB ID pin (FS or HS) in a USB-C scenario? Do I leave it floating, grounded, or does it need to be connected to one or both of CC1\2 ?

2 - Regarding USB connectivity, can I connect in parallel the following MCU pins (since both sets are inputs to the STM MCU)

  pin 69 (FS_ID) to pin 51 (HS_ID)?

  pin 68 (FS_VBUS) to pin 52 (HS_VBUS)?

3 - For question 2, when using a H723 MCU, pins 51 & 52 would be configured as GPIO inputs. When using a F723 either USB mode could be used, so its possible pins 68 & 69 would be configured as GPIO inputs instead. Would this parallel connectivity idea adversely affect FS_ID and FS_VBUS operation? (I suspect not as these signals are 99% static DC levels).

 

[TDK]

If the STM is always operating as a USB device (as opposed to a USB host), the ID pin should be grounded on the PCB and does not need connected to the STM32. It's only needed for OTG oepration.

If the device is bus-powered, VBUS does not need connected. If the device is self-powered, connect VBUS to a GPIO pin and de-initialize the USB pins when VBUS power goes away.

There's no problem connecting two pins to VBUS if they're both inputs. Use a resistor bridge.

 

Having a single PCB be compatible with two chips like this seems non-optimal. Unless there is a clear, compelling reason, choose a single chip. You will spend less time on things that don't impact the device operation and more time developing useful functionality.

[Bags]

Thanks for the Sunday feedback :o)

Depends on what you are optimizing for.... In my case its just one PCB to design and get made, that can support which ever MCU \ USB mode that has enough umph to run my app at max load (which is as yet undetermined as I need a platform with the custom comms h/w on it in order to bench test it).

If it turns out the H723 can do it just using USB FS, I can jury rig an F446 to the PCB h/w to see if that would work as a cheaper alternative MCU - which reminds me... to Kicad in some more pads \ pins to the PCB to facilitate that test plan.

Its my first USB project and first time using STM32 MCUs, so every days a school day!

 

[FBL]

Hi @Bags 

I would also add that you can start with ST's reference designs : reference boards and firmware example. For reference, MB1814 page 7.

[TDK]

@Bags You should mark someone else's reply as the solution rather than your own. This helps other people find the best answer to the question in the opening post.