Overview of USB Type‑C Interface, Data and Power Roles, and PD Charging Process

Since its first release in 1998, the USB standard has evolved through many connector types (A, B, Mini‑A/B, Micro‑A/B, etc.), leading to a variety of cables and adapters. The USB‑IF organization has defined numerous interface specifications over the past two decades.

For the USB Type‑C connector, the standardization body introduced a reversible plug design and defined the E‑Marker functionality. An E‑Marker‑enabled cable can report its current‑carrying capability, cable ID, and other characteristics. Power for the E‑Marker is supplied via the VCONN line, detected through a pull‑down resistor (Ra) on the source side.

The Type‑C interface supports a maximum data rate of 10 Gb/s (USB 3.1 Gen2) and can operate in 4‑lane DisplayPort mode for high‑resolution video. On the power side, it can deliver up to 100 W (20 V / 5 A).

Role negotiation is performed through the Configuration Channel (CC) pins. The CC pins enable the detection of the device role (Host or Device) and, with the advent of USB‑PD, also carry half‑duplex communication for power‑delivery negotiation.

Data Role definitions :

DFP (Downstream Facing Port): typically a host or hub that provides VBUS and VCONN and can receive data.

UFP (Upstream Facing Port): typically a device (e.g., flash drive) that draws power from VBUS and can send data.

DRP (Dual‑Role Port): can act as either DFP or UFP and switch dynamically, common in laptops.

Power Role definitions include Source‑Only, Sink‑Only, and various dual‑role modes (e.g., default Source that can swap to Sink via PD, Source/Sink rotation, Sourcing Device such as a monitor, Sinking Host such as a laptop).

The two CC pins in a Type‑C receptacle are used for:

Detecting cable insertion and orientation.

Establishing the Data Role between the connected ports.

Configuring VBUS (through pull‑up/pull‑down resistors) during PD negotiation.

Providing VCONN power when needed.

Enabling optional modes such as audio accessory detection.

PD (Power Delivery) charging communication process :

The PD protocol is a fast‑charging standard that runs over the CC lines. After a cable is connected, SOP messages are exchanged to advertise the source’s voltage/current capabilities (e.g., 5 V, 9 V, 12 V, 15 V, 20 V). The sink queries these capabilities, selects a suitable pair (e.g., 9 V), and sends a Request message. The source acknowledges with an Accept message and adjusts its power supply accordingly. The sink then configures its charger IC to the negotiated voltage/current. Throughout charging, the sink may send additional Request messages to change the output, enabling dynamic fast‑charging.

Key steps of the PD negotiation:

The charger broadcasts its supported voltage/current profiles via the CC line.

The device’s policy engine monitors the CC line, decodes the SourceCapabilities message, and extracts the list of profiles.

The device selects a profile and sends a Request message with the desired voltage/current.

The charger decodes the request, sends an Accept message, and adjusts its output.

The device configures its charging IC to the new parameters.

The device can later send additional Request messages to modify the output for faster charging.