How to connect the CC Pin when make USB type C compatible to USB2.0

[Dat Tran]

Hi every body, current we have a problem when make compatible between USB2.0 and type C on our devices.

We don't want full type C's feature yet. We just wanted our firmware to be compatible with type C cable on some laptop which have only type C connection.

So we pulled down 2 CC (CC1 and CC2) pin with 5.1Kohm. It likely work fine if we connected our devices to the laptop directly. But when we use Hub, the laptop doesn't recognize our devices.

We looked at some documents, especially on https://www.st.com/resource/en/technical_article/dm00496853-overview-of-usb-type-c-and-power-delivery-technologies-stmicroelectronics.pdf

"There are two CC pins in each receptacle, but only one is connected through the cable to establish communication. The other pin can be re-assigned as the VCONN pin for powering electronics in the USB Type-C™ plug of electronically-marked cables."

Does that mean, no matter CC1 or CC2, only one CC pin needs to pull down, leave other one not connected? Because we are currently pull down both CC1 and CC2.

Also, ST says need 5.1Kohm resistor, any one know these value stand for?

Thank a lot for the help.

[TDK]

See "Table 3-20 USB Type-C to USB 2.0 Micro-B Receptacle Adapter Assembly Wiring" in the USB spec to see how to wire pins to covert the USB C pinout to the USB micro pinout.

This page also covers it:

https://www.dcddcc.com/blog/2018-11-10-retrofitting-the-seek-thermal-compact-with-a-usb-type-c-connector-using-3d-printing.html

The ST document you're referring to goes into how to handle power delivery functions. That's not something USB2 has, so it's not relevant.

[Dat Tran · Accepted solution]

Thanks a lot, that is clear. so both CC1 and CC2 need to pull down 5.1K which what we have. Not sure why it doesn't work if connect through hub

[paolo239955_stm1_stmicro_com]

From USB C specifications:

For the device, the location of the USB SuperSpeed data bus, USB 2.0 data bus, CC and VCONN pins are fixed by design. Given that the device pin locations are fixed, only two possible connected states exist when viewed by the host.

In the case of a USB 2.0 device, using a USB Type C connector only CC1 must be connected to the pull down resistor. VCONN (CC2) can be left floating.

[Nicolas P.]

Hello @paolo239955_stm1_stmicro_com​ 

No you must drive both CC pins with one different Rd pull down resistor. Because you don't know how the cable will be plugged. And in case of EMC (Electonically Marked Cable) only one CC line is going from one end to the other.

For information, we now have STM32 MCUs with internal drive of the CC lines. (STM32G0, STM32G4, STM32L5, STM32U5...).

We also have some protection ICs (TCPP = Type C Port Protection) is you want to do power delivery.

See Wiki. TCPP01 has internal pull down resistor, and it can protect from over voltage, shortcuts and others...