Introduction to the Type-C Interface

The Type-C interface is a fully upgraded connection standard first officially introduced by the USB Implementers Forum in the USB 3.1 specification released in 2014. It defines a completely new set of USB physical specifications, including connectors, ports, receptacles, and cables. With its compact size, reversible plug-in design, extremely high data transfer speed, and powerful power-delivery capability, the Type-C interface is widely used in consumer electronics, industrial equipment, automotive applications, and more.

Type-C is only one of the three connector types introduced in the USB 3.1 standard, which includes USB Type-A, USB Type-B, and USB Type-C. USB Type-A and USB Type-B have long been widely used in traditional computers, printers, and other devices. So why introduce USB Type-C?

As more and more new devices pursue lightweight, miniaturized, standardized, and unified designs, the “bulky” size of traditional USB connectors can no longer meet the needs of manufacturers and consumers.
At the same time, the inconvenience of traditional USB connectors—where users must repeatedly plug and unplug to find the “correct” orientation—has long been criticized. Users urgently need a connector similar to Apple’s Lightning interface that allows insertion from both sides, especially for devices such as mobile phones.

Features of the Type-C Interface

As the current mainstream connector standard, the core features of Type-C can be summarized as follows:

· Smaller size: The Type-C connector measures 8.4 mm × 2.6 mm, which is smaller than traditional USB connectors.

· Reversible orientation: The interface adopts a symmetrical top-and-bottom design, allowing insertion in both directions, and supports up to 10,000 insertion cycles.

· High-speed data transfer: Type-C supports the latest USB4 standard, with a maximum transfer rate of up to 40 Gbps.

· Strong power delivery capability: Through the USB PD protocol, Type-C enables bidirectional power delivery + high-power output, supporting up to 240 W of power transmission. The interface also supports reverse charging—for example, when a phone is connected to a laptop's Type-C port, it can charge the phone.

· High expandability: With Alternate Mode (Alt Mode), it can dynamically reassign interface pins to support multiple protocols. For example, it can support DP 1.4 and output video at 4K or even 8K resolution. Some devices also support audio output.

· Multi-protocol compatibility: A single Type-C port can support USB data transfer, PD fast charging, audio/video output, external expansion, and even Thunderbolt protocols simultaneously.

Type-C Interface Definition

The Type-C interface consists of a receptacle (female) and a plug (male). To suit different application scenarios and cost requirements, several versions of Type-C exist, including the full-featured 24-pin version, the USB 2.0–only 16/12-pin versions, and the charging-only 6-pin version.

【24-Pin Type-C Interface Definition】

The 24-pin Type-C interface provides full support for all protocols. As shown in the diagram (not included here), the receptacle uses 24 pins and the plug uses 22 pins, both with a symmetrical layout that enables reversible plug insertion.

Compared to the receptacle, the plug has only one pair of D+/D– signals (the receptacle has two pairs) and uses one CC1 + VCONN set (the receptacle has CC1 + CC2).
This is because USB 2.0 requires only one differential pair (D+/D–) for data transmission. Therefore, regardless of whether the plug is inserted forward or reversed, a single pair of D+/D– lines is sufficient.

As for the CC1 + VCONN design:

· The plug only needs the CC1 pin to detect the orientation.

· If the receptacle detects voltage change on CC1, the plug is inserted forward; if CC2 changes, it is inserted in reverse.

· VCONN is used to power the electronic marker chip inside active cables (typically 3.3V or 5V).

The full 24 pins of a Type-C connector and their functions are as follows:

· VBUS: 4 pins. These supply bus power between devices. Regardless of orientation, all four VBUS pins provide power. They commonly support 5V, 9V, 12V, 15V, and 20V, with a maximum current of 5A.

· GND: 4 pins. These serve as the return path for power. All four GND pins are active regardless of orientation.

· TX+/TX– and RX+/RX–: 4 differential pairs used for USB 3.1 Gen 1 and higher-speed data transmission.

· D+/D–: 2 pins used for USB 2.0 data transmission.

· CC1/CC2: Configuration Channel pins used to detect connection status, determine plug orientation, and negotiate power delivery and data roles.

· SBU1/SBU2: Sideband Use pins used in Alternate Modes for transporting additional signals, such as DP or Thunderbolt auxiliary signals.

· VCONN: When one CC pin is used for orientation detection, the other CC pin becomes VCONN. Its function is to power the e-marker chip inside active cables (which stores information such as supported power levels, data capabilities, and cable identity). VCONN typically provides 3.3V or 5V.

The 16-pin Type-C connector is derived from the full-featured 24-pin version by removing the USB 3.0 TX1/2 and RX1/2 pins, while retaining the SBU1/2, CC1/2, and D+/D– pins. Apart from not supporting USB 3.0/3.1 high-speed data transfer, it functions identically to the full version and still supports PD fast charging, audio/video transmission, and other features.

The 12-pin Type-C connector uses fewer pins to achieve the same functionality. In essence, it is no different from the 16-pin version and can share the same PCB footprint. During design, two pairs of VBUS and GND pins on both ends of the receptacle are placed closer together. Note that they are only placed closer—not merged—so electrically the interface still has 16 pins, but the PCB footprint only needs 12 pins.

The 6-pin Type-C connector focuses solely on fast-charging capabilities. It retains only the VBUS, GND, CC1, and CC2 pins. VBUS and GND are arranged symmetrically on both sides of the connector. CC1 and CC2 support reversible insertion and fast-charging protocol negotiation.

Type-C Interface PD Protocol

The USB Power Delivery (USB PD) protocol is a fast-charging standard based on the Type-C interface. Its core function is to enable flexible and safe power transmission through communication and negotiation over the CC pins. It includes key processes such as role identification, capability negotiation, and voltage adjustment. The detailed working principles are as follows:

(1) Connection Detection and Role Identification

When a C-to-C cable is connected, the Source detects the device connection through voltage changes on the CC pin. At the same time, it determines the initial roles of both sides (Source/Sink) based on the pull-up/pull-down configuration on the CC pin. Devices that support DRP (Dual-Role Power) can switch roles later.

(2) Capability Advertisement

The Source actively sends a Source_Capabilities message to the Sink, announcing the power profiles it supports (e.g., 5V/3A, 9V/2A, 20V/5A, etc.).
The data is encoded using BMC and transmitted through the CC pin.

(3) Power Request and Confirmation

After receiving the capability list, the Sink selects a suitable power profile based on its needs (e.g., battery status or charging strategy) and sends a Request message (such as requesting 9V/2A).
The Source verifies whether the request is within its supported range. If valid, it responds with an Accept message.

(4) Voltage Adjustment and Power Delivery Start

The Source’s PD controller adjusts the internal power circuit (such as a buck converter) to reach the negotiated voltage (e.g., from the default 5V up to 9V).
Once the output voltage stabilizes, the Source sends a PS_RDY message to inform the Sink. Power delivery then officially begins through the VBUS line.