Traditional USB 2.0 interface to Type-C conversion solution based on STM32

       The topic of USB Type-C interface has become very popular, and many companies have launched Type-C related chips. Its advantages are mainly reflected in its dual-sided connection, fast transmission speed, strong power supply, and support for audio and video transmission.

      We know that most STM32 chip models are equipped with USB DEVICE or USB OTG modules. With the continuous promotion and popularization of the Type-C interface, the question of how to connect the USB module of the STM32 chip to the Type-C interface will naturally gradually appear in front of STM32 application engineers.

      ST official application note [AN4775] introduces the solution suggestions on how to replace the traditional USB 2.0 connector with USB Type-C. At the same time, the note also briefly introduces some basic knowledge about USB Type-C and USB power transmission.

      Here we might as well take a look at some terms and pin diagrams of the USB Type-C interface.

1. Several terms of USB Type-C interface
DFP [Downstream Facing Port]: Downstream port. It is related to USB data flow. Generally refers to the port of HOST or HUB, and the slave device is connected to such port.
UFP [Upstream Facing Port]: Upstream port. It is related to USB data flow. Generally refers to DEVICE port or HUB port connected to other HOST or DFP HUB.
SOURCE: Power supply port. The CC pin on this port is connected to a pull-up resistor and supplies power to the outside through VBUS. Generally refers to HOST or DFP HUB port, such as the traditional Type-A port.
SINK: Power receiving port: The CC pin on this port is connected to a pull-down resistor, and it draws power from VBUS. Generally refers to device port, such as the traditional Type-B port.
DRP [Dual Role Port] Dual role port. A port that can be used as both SOURCE and SINK, and the role can be fixed or negotiated.

2. USB Type-C interface pin diagram
The USB Type-C interface has a total of 24 pins, divided into symmetrical connection and asymmetrical connection.
Symmetrical connection:
-USB 2.0 differential signal pair (D+/D-);
-Power pin: VBUS/GND;

Asymmetric connection:
- Two sets of TX/RX signal pins supporting USB3.1 data transmission speed;
- Channel configuration pins [CC pins], used for configuration management such as plug-in and role monitoring, power supply, etc.;
- Two sideband signal pins [SBU], used for analog audio mode or DP alternative mode;

   From the pin diagram above, we can see two CC configuration pins, CC1 and CC2. However, for a plug in one direction, only one CC pin is connected to it. For two CC pins, a DFP port must be connected to a pull-up resistor Rp; a UFP port must be connected to a pull-down resistor Rd. The insertion direction and device role are confirmed by detecting the level of the Rp/Rd resistor connected to the CC pin.

 

   Finally, let's take a look at the example schematic diagram provided by ST for the STM32 chip with different roles to switch from the traditional USB 2.0 interface to the Type-C interface. It is clear at a glance and you can refer to it when needed.