What is the minimal configuration required to support USB C PD on the STM32G071 line?

[NHeid.2]

Hello everyone! I'm very new to USB C PD so bear with me.

I'm currently designing a very simple temperature controller board that uses a USB C PD power supply. I am using a STM32G071C8U3 as the host MCU.

I have connected the CC1 (PA8) and CC2 (PB15) lines to the equivalent on the USB C port and am regulating the voltage from VBUS to 3.3V for the MCU. I've been assuming that plugging in will first deliver some voltage over VBUS in the USB PD range (3V-21V or something like that) and then the micro can negotiate the desired voltage/current, but when I plug in the USB C PD I get 0V on VBUS. What could I be missing?

When I plug in a non PD capable supply, everything seems to work find and I get 5V on VBUS and the MCU turns on correctly. But plugging in the USB C PD gets nothing. I've confirmed this USB C PD works by hooking it up to the STM32 GO.

Thanks for your time!

[Nicolas P. · Accepted solution]

Hello @NHeid.2​ 

first question to answer : have you set some pull down (Rd) resistors on the UCPD block ?

In type C, you have to configure pull up or pull down resistors to indicate which will be your power role.

Have a look at the wiki, or the AN5225 (page 24).

If you just need 5V, no more, no negociation, you just have to set fixed pull down resistors.

This can be achieved either using the dead battery pins (DB), or by driving the UCPD block.

Only this way a power delivery source will provide VBUS.

[NHeid.2]

Thank you very much! I will go through the material you've provided and try the changes you've suggested.