USB VBus Sensing during USB 2.0 Full Speed Communication

[Circuit]

Hi

I have a USB-C Connector that will be used for Power Delivery Sink  for charging and USB Full Speed Mode(12Mbps) for communicating with onboard STM32F767ZIT6. But only one thing will happen at a time. 

 

As seen in the attached schematics, I have used STUSB4500 as PD Sink controller. I will communicate with it via I2C using STM32. I understand that this STUSB4500 will negotiate 20V(60W which i want for charging) with the source(which in this case is AC-DC Wall adapter) in Power Delivery Mode.

But my question is during USB Full Speed Mode Communication with STM32, when that USB-C Receptable is connected to a PC instead of Wall Adapter. As during charging mode, USB_VBus is 20V and in Full Speed mode, it is 5V and my STM32 is Self-Powered and VBus sensing is mandatory.

But due to USB VBus varying between 5V and 20V, I cant connect it to for example PA9 VBus sensing pin of STM32 using a voltage divider. 

So, i was thinking maybe there is another option to sense VBus(5V) in Communication Mode. And that would be maybe connecting one of the Pins from STUSB4500 to STM32 to let it know VBUS is present? But i am unsure which  Pin is best suited for this job ATTACH/GPIO Pin or anything else?

 

Thanks!

 

 

 

 

 

[TDK]

Duplicate:

USB-C Connector for Power Delivery and communicati... - STMicroelectronics Community

 

Use a clamping diode to keep the voltage in the correct level, or use an ADC pin along with a resistor divider which can accept the full range.

For example, a schottky diode between the middle of the resistor and the bridge to 3.3 V will prevent it from causing overvoltage, yet still allow it to read 1 when the voltage is 5 V or 20 V.

[Circuit]

Thanks!

 

But isn't using ATTACH/GPIO Pin from STUSB4500 to indicate STM32 that USB VBUS is present an easier solution? or do you see any drawback with that? 

[Didier HERROUIN]

Hello Circuit,

The ATTACH pin is perfect for your need, as it is tied to GND by STUSB4500 when a valid source-to-sink connection is established. 

Regards,

Didier Herrouin