How Type-C works

Latest update time：2024-10-27

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This chapter will mainly analyze the working principle of Type-C. If you are interested, don’t forget to follow Masi Tuyuan!

Previous chapter: Understanding Type-C and fast charging related knowledge

This chapter can help you solve the following problems:

Type-C can be plugged in blindly, so why do we have to plug it in the right way up and the wrong way down?

What is the function of Type-C CC?

What are the functions of Type-C extension?

1. Type-C Port Behavior and System Model

1.1 Type-C Port Behavior

The functions of USB Type-C are roughly divided into two types: power supply and data transmission ; under different functions, it has different roles and behaviors:



    Power Supply



    Data Transmission

Power roles：

Source: In the role of power supply, it can provide power to the Sink end, such as one end of the charger;
Sink: The power consumption role, which will consume Vbus Power when included in the Source, such as a power bank;
Dual-Role-Power: As a power source or sink, it can be switched dynamically. A typical DRP device is a laptop. The role of the device when it is first connected is determined by the port's Power Role; it can also be changed later through the switch process. DRP

Data roles：

DFP-mode only: Downstream Facing Port, which is equivalent to the Host role in USB, and is equivalent to the USB of the vehicle host;
UFP-mode only: Upstream Facing Port, equivalent to the Device role in USB, equivalent to a USB flash drive;
Dual-Role Data: DRD dual role, which means it can play two roles. It can be configured to switch in the software, which is equivalent to the USB of a mobile phone.

The figure shows corresponding device examples for and .



    Data Role



    Power Role

Another point to mention is the distinction between the roles of USB : The USB bus is a master-slave data bus. In a bus, there can only be one USB host, and the others are slaves. This is how normal communication can be achieved. This has been considered in the early design stage and has been designed in the protocol communication.



    Host



    Device

1.2 USB Type-C System Implementation Model

The USB Type-C system implementation model is mainly divided into three parts: the communication interface on the left, Type-C management in the middle, and power supply on the right; this part has corresponding software coding, communication, control, and charging management. Mainly in the middle part:

USB Type-C Port Controller

• Port Power Control for VBUS and VCONN

• USB Power Delivery PHY

• CC Logic Function

USB Type-C Port Manager

• Port Policy Engine

• USB Power Delivery Protocol

• Interface to system software via UCSI

2. Type-C CC pin function

Positive insertion: A1 to A1

Reverse insertion: A1 to B1

Key points to check :

CC1 / CC2 (Configuration Cannel) : detect whether the cable is plugged in the forward or reverse direction, detect whether the cable is connected, determine which side is the DFP (Downstream Facing Port) and UFP (Upstream Facing Port), configure Vbus, configure Vconn, configure other modes (alternate or accessory mode), PD communication, etc. In short, CC manages the communication between the master and slave ends through the USB type C cable.

2.1 Detecting USB port roles

Detect the connected device and judge the status by checking whether the other party is pulled up or down through the CC pin. The general table is as shown in the figure:

The table mainly judges based on the pin status of CC1 CC2. There are 6 states for current connection. The last one , Type-C headset is a typical application; Audio Apdapter Mode attached

For example: you can see that CC1 and CC2 are both in the pull-down state.

2.2 Identify cable direction and establish signal routing

The USB Type-C connector has no directionality, so it doesn't matter whether it is plugged in the right way or the wrong way. However, it needs to be identified internally. USB 3.2 Gen2x2 and USB 4.0 Gen1x2 also need to identify which of the two differential pairs is LANE1. Therefore, cable identification is a must for USB Type-C.

2.3 Two DRP connection negotiation

For both connections In this case, it can be used as a power supply or a power consumption. When DPR is connected to a UFP device, DRP will be converted to DFP. When DRP is connected to a DFP device, DRP will be converted to UFP.

DRP

From the figure, we can see that CC1 and CC2 both contain a switch control. During the negotiation process, the chip will control the pull-up, pull-down, floating and other states.

2.4 Configuring VCONN

The Type-C specification defines an active cable with internal circuits that need power. There are two CC pins on the Type-C cable. If one of them is used to identify DFP and UFP, the other can be used as VCONN to provide power for the active cable. When the DFP detects that the pull-down resistor is Ra=800~1200Ohms, this CC pin will switch to VCONN to output 4.75~5.5V to the outside, with a maximum power of 1W.

2.5 Discover and configure VBUS

Discover and configure VBUS. This part should belong to Type-C power supply, which is mostly used for fast charging related functions. For USB Type-C to provide the maximum current, the CC pin is required for detection. The Type-C port can provide 5V/3A, but if the USB PD protocol is used in conjunction, the power supply capacity will be greatly improved. The USB PD protocol transmits protocol data through the CC pin and is responsible for power negotiation and management. The CC pin is used to discover the device connection status and perform more complex power negotiation through USB PD.

First, the DFP needs to detect the currently connected USB role. Please refer to 2.1 Detecting the USB port role.

Device discovery and negotiation :

CC pin detection : When a device is connected to a Type-C port, the resistance value of the CC pin can determine the capabilities of the power source and the current requirements of the device.

CC: DFP informs UFP of its power supply capability through the voltage on the CC pin. The pull-down resistor Rd=5.1K on the UFP end, and DFP can generate voltage on the CC pin through its pull-up resistor or current source.

The current source specifications for the resistance value are shown in the figure:

USB PD negotiation : Through the CC pin, the device can communicate with the power source using the USB PD protocol. The USB PD protocol allows the device and the power source to dynamically negotiate current, voltage, and power to ensure that the required power can meet the demand.

2.6 Type-C Other functions

Regarding other functions of Type-C, the major Type-C specification defines the alternative (Alt) mode and the peripheral (Accessory) mode. These two modes enable the USB Type-C interface to not only transmit data and power, but also support a variety of external devices and functions.

2.6.1 Alternate Mode (Alt Mode)

The alternative mode allows the USB Type-C interface to support data transmission of non-USB protocols. Through this mode, different protocols or standards can be used on the same interface to achieve more functional expansion.

Function : Alternate mode enables the Type-C interface to transmit video signals such as HDMI, DisplayPort, MHL, and other proprietary data protocols.

Application scenarios: video output, audio and data, external interface;

2.6.2 Accessory Mode

Peripheral mode is used to define the behavior of external accessories connected to the USB Type-C port. Unlike alternate mode, the focus of peripheral mode is on the accessory functionality between the device and the host, rather than on the replacement of the data protocol.

Function : Allows external accessories such as keyboard, mouse, headset, etc. to connect to the host device and communicate through the USB Type-C interface.

Application scenarios :

External accessories : Peripherals such as keyboards, mice, and headphones can be connected to the host device in peripheral mode to provide input and output functions.
Peripheral devices : For example, a USB Type-C to Ethernet adapter that can make network connections in peripheral mode.

2.6.3 Extended Application

Type-C commonly transmits HDMI signals, DisplayPort signals, and Type-C headphones on mobile phones transmit audio signals, and Type-C external graphics cards have also appeared.

3. Conclusion

This chapter mainly analyzes the working principle of , which mainly includes data transmission and power supply. In addition, it mainly analyzes the CC pin, and the focus is also on CC. Understanding the CC pin will also give you a deeper understanding of Type-C. Since Type-C is widely used, it has greatly improved not only in charging, but also in data transmission, with technical iterations and a lot of knowledge points. It has become a trend. Although there are still many ports, I believe will take the throne.



    Type-C



    Type-C



    Type A



    Type-C

In addition, when it comes to cable selection, it is recommended to choose this full-featured cable, which can realize all functions and has good quality. Type-C

Reference official website:

https://www.usb.org/sites/default/files/D1T1-2%20-%20USB%20Type-C%20System%20Overview.pdf

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