USB-C

USB Type-C and USB-C are trademarks of the USB Implementers Forum.[8]

USB-C plug with a MacBook Pro laptop

USB-C port (receptacle) on an Android mobile phone

The 24-pin double-sided connector is slightly larger than the micro-B connector, with a USB-C receptacle measuring 8.4 millimetres (0.33 in) wide, 2.6 millimetres (0.10 in) high, and 6.65 millimetres (0.262 in) deep. Two kinds of connectors exist, plug and receptacle; the gender terms female and male are not used in USB, avoided for clarity given that all USB plugs are male and receptacles female.

Plugs are found on cables and adapters. Receptacles are found on devices and adapters.

USB 3.1 cables are considered full-featured USB-C cables. They are electronically marked cables that contain a chip with an ID function based on the configuration channel and vendor-defined messages (VDM) from the USB Power Delivery 2.0 specification. Cable length should not exceed 2 metres (6 ft 7 in) for Gen 1, and 1 metre (3 ft 3 in) for Gen 2.[9] The electronic ID chip provides information about product/vendor, cable connectors, USB signaling protocol (2.0, Gen 1, Gen 2), passive/active construction, use of V_CONN power, available V_BUS current, latency, RX/TX directionality, SOP controller mode, and hardware/firmware version.[6]

USB-C cables that do not have shielded SuperSpeed pairs, sideband use pins, or additional wires for power lines can have increased cable length, up to 4 metres (13 ft). These USB-C cables only support USB 2.0 (up to 480 Mbit/s) and do not support Alternate Modes. Active cables (those with built-in repeaters) can support SuperSpeed USB 5Gbps (= USB 3.2 Gen 1x1 = USB 3.1 Gen 1 = UBS 3.0) only over lengths up to 10 metres (33 ft).

All USB-C cables must be able to carry a minimum of 3 A current (at 5 V, for 15 W) but some can carry 5 A current (at 20 V, for 100 W).[10] USB-C to USB-C cables supporting 5 A current must contain e-marker chips (also marketed as E-Mark chips) programmed to identify the cable and its current capabilities. USB charging ports should be clearly marked with power capability.[11]

Full-featured USB-C cables that implement USB 3.1 Gen 2 can provide 10 Gbit/s (full duplex) signalling rate. They are marked with a SuperSpeed USB 10Gbps (previously marketed as SuperSpeed+) logo. There are also cables which can support only USB 2.0 with a nominal data rate of 480 Mbit/s (with maximal effective data rate of ~40MB/s). The USB Implementers Forum certifies valid cables so they can be marked accordingly and users can distinguish them from non-compliant products.[12]

For any two pieces of equipment connecting over USB, one is a host (with a downstream-facing port, DFP) and the other is a peripheral device (with an upstream-facing port, UFP). Some products, such as mobile phones, can take either role, whichever is opposite that of the connected equipment. Such equipment is said to have Dual-Role-Data (DRD) capability, which was known as USB On-The-Go in the previous specification.[13] With USB-C, when two such devices are connected, the roles are first randomly assigned, but a swap can be commanded from either end, although there are optional path and role detection methods that would allow equipment to select a preference for a specific role. Furthermore, Dual-Role equipment that implements USB Power Delivery may swap data and power roles independently using the Data Role Swap or Power Role Swap processes. This allows for charge-through hub or docking station applications such as a portable computer acting as a host to connect to peripherals but being powered by the dock, or a computer being powered by a display, through a single USB-C cable.[6]

USB-C devices may optionally provide or consume bus power currents of 1.5 A and 3.0 A (at 5 V) in addition to baseline bus power provision; power sources can either advertise increased USB current through the configuration channel or implement the full USB Power Delivery specification using both the BMC-coded configuration line and the legacy BFSK-coded V_BUS line.[6][11]

All older USB connectors (all Type-A and Type-B) are designated legacy. Connecting legacy and modern, USB-C equipment requires either a legacy cable assembly (a cable with any Type-A or Type-B plug on one end and a Type-C plug on the other) or, in very specific cases, a legacy adapter assembly.

An older device can connect to a modern (USB-C) host by using a legacy cable, with a Standard-B, Mini-B, or Micro-B plug on the device end and a USB-C plug on the other. Similarly, a modern device can connect to a legacy host by using a legacy cable with a USB-C plug on the device end and a Standard-A plug on the host end. Legacy adapters with USB-C receptacles are "not defined or allowed" by the specification because they can create "many invalid and potentially unsafe" cable combinations (being any cable assembly with two A ends or two B ends). However, exactly two types of adapter with USB-C plugs are defined: one with a Standard-A receptacle (for connecting a legacy device (such as a flash drive—not a cable) to a modern host, and supporting up to USB 3.1), and one with a Micro-B receptacle (for connecting a modern device to a legacy host, and supporting up to USB 2.0).[14]

A device with a USB-C port may support analog headsets through an audio adapter with a 3.5 mm jack, providing three analog audio channels (left and right output and microphone). The audio adapter may optionally include a USB-C charge-through port to allow 500 mA device charging. The engineering specification states that an analog headset shall not use a USB-C plug instead of a 3.5 mm plug. In other words, headsets with a USB-C plug should always support digital audio (and optionally the accessory mode).[15]

Analog signals use the USB 2.0 differential pairs (Dp and Dn for Right and Left) and the two side-band use pairs for Mic and GND. The presence of the audio accessory is signaled through the configuration channel and V_CONN.

An Alternate Mode dedicates some of the physical wires in a USB-C cable for direct device-to-host transmission using non-USB data protocols, such as DisplayPort or Thunderbolt. The four high-speed lanes, two side-band pins, and (for dock, detachable device and permanent-cable applications only) five additional pins can be used for Alternate Mode transmission. The modes are configured using vendor-defined messages (VDM) through the configuration channel.

The USB Type-C specification 1.0 was published by the USB Implementers Forum (USB-IF) and was finalized in August 2014.[4]

It defines requirements for cables and connectors.

• Rev 1.1 was published 2015-04-03[16]
• Rev 1.2 was published 2016-03-25[17]
• Rev 1.3 was published 2017-07-14[18]
• Rev 1.4 was published 2019-03-29[18]
• Rev 2.0 was published 2019-08-29[19]
• Rev 2.1 was published 2021-05-25 (USB PD - Extended Power Range - 48 V - 5 A - 240 W)[20]
• Release 2.2 was published 2022-10-18, primarily for enabling USB4 Version 2.0 (80 Gbps) over USB Type-C connectors and cables.[14]

Adoption as IEC specification:

• IEC 62680-1-3:2016 (2016-08-17, edition 1.0) "Universal serial bus interfaces for data and power – Part 1-3: Universal Serial Bus interfaces – Common components – USB Type-C cable and connector specification"[21]
• IEC 62680-1-3:2017 (2017-09-25, edition 2.0) "Universal serial bus interfaces for data and power – Part 1-3: Common components – USB Type-C Cable and Connector Specification"[22]
• IEC 62680-1-3:2018 (2018-05-24, edition 3.0) "Universal serial bus interfaces for data and power – Part 1-3: Common components – USB Type-C Cable and Connector Specification"[23]

Type-C receptacle pinout (end-on view)

The receptacle features four power and four ground pins, two differential pairs (connected together on devices) for legacy USB 2.0 high-speed data, four shielded differential pairs for Enhanced SuperSpeed data (two transmit and two receive pairs), two Sideband Use (SBU) pins, and two Configuration Channel (CC) pins.

Type-C plug pinout (end-on view)

The plug has only one USB 2.0 high-speed differential pair, and one of the CC pins (CC2) is replaced by V_CONN, to power optional electronics in the cable, and the other is used to actually carry the Configuration Channel (CC) signals. These signals are used to determine the orientation of the cable, as well as to carry USB Power Delivery communications.

USB Type-C Locking Connector Specification

The USB Type-C Locking Connector Specification was published 2016-03-09. It defines the mechanical requirements for USB-C plug connectors and the guidelines for the USB-C receptacle mounting configuration to provide a standardized screw lock mechanism for USB-C connectors and cables.[24]

USB Type-C Port Controller Interface Specification

The USB Type-C Port Controller Interface Specification was published 2017-10-01. It defines a common interface from a USB-C Port Manager to a simple USB-C Port Controller.[25]

USB Type-C Authentication Specification

Adopted as IEC specification: IEC 62680-1-4:2018 (2018-04-10) "Universal Serial Bus interfaces for data and power - Part 1-4: Common components - USB Type-C Authentication Specification"[26]

USB 2.0 Billboard Device Class Specification

USB 2.0 Billboard Device Class is defined to communicate the details of supported Alternate Modes to the computer host OS. It provides user readable strings with product description and user support information. Billboard messages can be used to identify incompatible connections made by users. They optionally appear to negotiate multiple Alternate Modes and must appear when negotiation fails between the host (source) and device (sink).

USB Audio Device Class 3.0 Specification

USB Audio Device Class 3.0 defines powered digital audio headsets with a USB-C plug.[6] The standard supports the transfer of both digital and analog audio signals over the USB port.[27]

USB Power Delivery Specification

Main article: USB Power Delivery

While it is not necessary for USB-C compliant devices to implement USB Power Delivery, for USB-C DRP/DRD (Dual-Role-Power/Data) ports, USB Power Delivery introduces commands for altering a port's power or data role after the roles have been established when a connection is made.[28]

USB 3.2 Specification

USB 3.2, released in September 2017, replaces the USB 3.1 standard. It preserves existing USB 3.1 SuperSpeed and SuperSpeed+ data modes and introduces two new SuperSpeed+ transfer modes over the USB-C connector using two-lane operation, doubling the data rates to 10 and 20 Gbit/s (1 and ~2.4 GB/s). USB 3.2 is only supported by USB-C, making micro-USB connectors obsolete.

USB4 Specification

The USB4 specification released in 2019 is the first USB data transfer specification to exclusively use the Type-C connector.

As of 2018, five system-defined Alternate Mode partner specifications exist. Additionally, vendors may support proprietary modes for use in dock solutions. Alternate Modes are optional; Type-C features and devices are not required to support any specific Alternate Mode. The USB Implementers Forum is working with its Alternate Mode partners to make sure that ports are properly labelled with respective logos.[29]

List of Alternate Mode partner specifications

Logo	Name	Date	Protocol	Status
	Thunderbolt Alternate Mode	Announced in June 2015[30]	USB-C is the native (and only) connector for Thunderbolt 3 and Thunderbolt 4 Thunderbolt 3 (also carries 4× PCI Express 3.0, DisplayPort 1.2, DisplayPort 1.4, USB 3.1 Gen 2),[30][31][32][33] Thunderbolt 4 (also carries 4× PCI Express 3.0, DisplayPort 2.0, USB4), Thunderbolt 5 (also carries 4× PCI Express 4.0, DisplayPort 2.1, USB4)	Current
	DisplayPort Alternate Mode	Published in September 2014	DisplayPort 1.2, DisplayPort 1.4,[34][35] DisplayPort 2.0[36]	Current
	Mobile High-Definition Link (MHL) Alternate Mode	Announced in November 2014[37]	MHL 1.0, 2.0, 3.0 and superMHL 1.0[38][39][40][41]	Current
	HDMI Alternate Mode	Announced in September 2016[42]	HDMI 1.4b[43][44][45][46]	Not being updated
	VirtualLink Alternate Mode	Announced in July 2018[47]	VirtualLink 1.0[48]	Abandoned

Other protocols like Ethernet[49] have been proposed, although Thunderbolt 3 and later are also capable of 10 Gigabit Ethernet networking.[50]

All Thunderbolt 3 controllers support both Thunderbolt Alternate Mode and DisplayPort Alternate Mode.[51] Because Thunderbolt can encapsulate DisplayPort data, every Thunderbolt controller can either output DisplayPort signals directly over DisplayPort Alternative Mode or encapsulated within Thunderbolt in Thunderbolt Alternate Mode. Low-cost peripherals mostly connect via DisplayPort Alternate Mode while some docking stations tunnel DisplayPort over Thunderbolt.[52]

DisplayPort Alternate Mode 2.0: DisplayPort 2.0 can run directly over USB-C alongside USB4. DisplayPort 2.0 can support 8K resolution at 60 Hz with HDR10 color and can use up to 80 Gbps, which is double the amount available to USB data.[53]

The USB SuperSpeed protocol is similar to DisplayPort and PCIe/Thunderbolt, in using packetized data transmitted over differential LVDS lanes with embedded clock using comparable bit rates, so these Alternate Modes are easier to implement in the chipset.[34]

Alternate Mode hosts and sinks can be connected with either regular Full-Featured Type-C cables, or with converter cables or adapters:

USB 3.1 Type-C to Type-C Full-Featured cable

DisplayPort, Mobile High-Definition Link (MHL), HDMI and Thunderbolt (20 Gbit/s, or 40 Gbit/s with cable length up to 0.5 m) Alternate Mode Type-C ports can be interconnected with standard passive Full-Featured USB Type-C cables. These cables are only marked with standard "trident" SuperSpeed USB logo (for Gen 1 cables) or the SuperSpeed+ USB 10 Gbit/s logo (for Gen 2 cables) on both ends.[54] Cable length should be 2.0 m or less for Gen 1 and 1.0 m or less for Gen 2.

Thunderbolt Type-C to Type-C active cable

Thunderbolt 3 (40 Gbit/s) Alternate Mode with cables longer than 0.8 m requires active Type-C cables that are certified and electronically marked for high-speed Thunderbolt 3 transmission, similarly to high-power 5 A cables.[30][33] These cables are marked with a Thunderbolt logo on both ends. They do not support USB 3 backwards compatibility, only USB 2 or Thunderbolt. Cables can be marked for both Thunderbolt and 5 A power delivery at the same time.[55]

Active cables and adapters contain powered electronics to allow for longer cables or to perform protocol conversion. The adapters for video Alternate Modes may allow conversion from native video stream to other video interface standards (e.g., DisplayPort, HDMI, VGA or DVI).

Using Full-Featured Type-C cables for Alternate Mode connections provides some benefits. Alternate Mode does not employ USB 2.0 lanes and the configuration channel lane, so USB 2.0 and USB Power Delivery protocols are always available. In addition, DisplayPort and MHL Alternate Modes can transmit on one, two, or four SuperSpeed lanes, so two of the remaining lanes may be used to simultaneously transmit USB 3.1 data.[56]

A simple USB 2.0/1.1 device mates using one pair of D+/D− pins. Hence, the source (host) does not require any connection management circuitry, but it lacks the same physical connector so therefore USB-C is not backward compatible. V_BUS and GND provide 5 V up to 500 mA of current.

However, to connect a USB 2.0/1.1 device to a USB-C host, use of Rd[57] on the CC pins is required, as the source (host) will not supply V_BUS until a connection is detected through the CC pins.

This means many USB-A–to–USB-C cables will only work in the A to C direction (connecting to a USB-C devices, e.g. for charging) as they do not include the termination resistors needed to work in the C to A direction (from a USB-C host). Adapters or cables from USB-C to a USB-A receptacle usually do work as they include the required termination resistor.

USB Power Delivery uses one of CC1, CC2 pins for power negotiation between source device and sink device, up to 20 V at 5 A. It is transparent to any data transmission mode, and can therefore be used together with any of them as long as the CC pins are intact.

USB power delivery has added 28V, 36V and 48V to support up to 240W of power for laptops, monitors, hard disks and other peripherals. USB-C is being positioned as the solution for mobile. [58]

In the USB 3.0/3.1/3.2 mode, two or four high speed links are used in TX/RX pairs to provide 5, 10, or 20 Gbit/s (only by USB 3.2 x2 two-lane operations) signalling rates respectively. One of the CC pins is used to negotiate the mode.

V_BUS and GND provide 5 V up to 900 mA, in accordance with the USB 3.1 specification. A specific USB-C mode may also be entered, where 5 V at nominal either 1.5 A or 3 A is provided.[59] A third alternative is to establish a USB Power Delivery (USB-PD) contract.

In single-lane mode, only the differential pairs closest to the CC pin are used for data transmission. For dual-lane data transfers, all four differential pairs are in use.

The D+/D− link for USB 2.0/1.1 is typically not used when USB 3.x connection is active, but devices like hubs open simultaneous 2.0 and 3.x uplinks in order to allow operation of both types of devices connected to it. Other devices may have the ability to fall back to 2.0, in case the 3.x connection fails.

In Alternate Modes one of up to four high speed links are used in whatever direction is needed. SBU1, SBU2 provide an additional lower speed link. If two high speed links remain unused, then a USB 3.0/3.1 link can be established concurrently to the Alternate Mode.[35] One of the CC pins is used to perform all the negotiation. An additional low band bidirectional channel (other than SBU) may share that CC pin as well.[35][43] USB 2.0 is also available through D+/D− pins.

In regard to power, the devices are supposed to negotiate a Power Delivery contract before an Alternate Mode is entered.[60]

The external device test system (DTS) signals to the target system (TS) to enter debug accessory mode via CC1 and CC2 both being pulled down with an Rd resistor value or pulled up as Rp resistor value from the test plug (Rp and Rd defined in Type-C specification).

After entering debug accessory mode, optional orientation detection via the CC1 and CC2 is done via setting CC1 as a pullup of Rd resistance and CC2 pulled to ground via Ra resistance (from the test system Type-C plug). While optional, orientation detection is required if USB Power Delivery communication is to remain functional.

In this mode, all digital circuits are disconnected from the connector, and the 14 bold pins can be used to expose debug related signals (e.g. JTAG interface). USB IF requires for certification that security and privacy consideration and precaution has been taken and that the user has actually requested that debug test mode be performed.

If a reversible Type-C cable is required but Power Delivery support is not, the test plug will need to be arranged as below, with CC1 and CC2 both being pulled down with an Rd resistor value or pulled up as Rp resistor value from the test plug:

This mirroring of test signals will only provide 7 test signals for debug usage instead of 14, but with the benefit of minimizing extra parts count for orientation detection.

In this mode, all digital circuits are disconnected from the connector, and certain pins become reassigned for analog outputs or inputs. The mode, if supported, is entered when both CC pins are shorted to GND. D− and D+ become audio output left L and right R, respectively. The SBU pins become a microphone pin MIC, and the analog ground AGND, the latter being a return path for both outputs and the microphone. Nevertheless, the MIC and AGND pins must have automatic swap capability, for two reasons: firstly, the USB-C plug may be inserted either side; secondly, there is no agreement, which TRRS rings shall be GND and MIC, so devices equipped with a headphone jack with microphone input must be able to perform this swap anyway.[61]

This mode also allows concurrent charging of a device exposing the analog audio interface (through V_BUS and GND), however only at 5 V and 500 mA, as CC pins are unavailable for any negotiation.

Plug insertions detection is performed by the TRRS plug's physical plug detection switch. On plug insertions, this will pull down both CC and VCONN in the plug (CC1 and CC2 in the receptacle). This resistance must be less than 800 ohms which is the minimum "Ra" resistance specified in the USB Type-C specification). This is essentially a direct connection to USB digital ground.

An increasing number of motherboards, notebooks, tablet computers, smartphones, hard disk drives, USB hubs and other devices released from 2014 onwards include the USB-C receptacles. However, the initial adoption of USB-C was limited by the high cost of USB-C cables[74] and the wide use of Micro-USB chargers.

Currently, DisplayPort is the most widely implemented alternate mode, and is used to provide video output on devices that do not have standard-size DisplayPort or HDMI ports, such as smartphones and laptops. All Chromebooks with a USB-C port are required to support DisplayPort alternate mode in Google's hardware requirements for manufacturers.[75] A USB-C multiport adapter converts the device's native video stream to DisplayPort/HDMI/VGA, allowing it to be displayed on an external display, such as a television set or computer monitor.

It is also used on USB-C docks designed to connect a device to a power source, external display, USB hub, and optional extra (such as a network port) with a single cable. These functions are sometimes implemented directly into the display instead of a separate dock,[76] meaning a user connects their device to the display via USB-C with no other connections required.

Many cables claiming to support USB-C are actually not compliant to the standard. Using these cables would have a potential consequence of damaging devices that they are connected to.[77][78][79] There are reported cases of laptops being destroyed due to the use of non-compliant cables.[80]

Some non-compliant cables with a USB-C connector on one end and a legacy USB-A plug or Micro-B receptacle (receptacles also being invalid on cables) on the other end incorrectly terminate the Configuration Channel (CC) with a 10 kΩ pull-up to V_BUS instead of the specification mandated 56 kΩ pull-up,[81] causing a device connected to the cable to incorrectly determine the amount of power it is permitted to draw from the cable. Cables with this issue may not work properly with certain products, including Apple and Google products, and may even damage power sources such as chargers, hubs, or PC USB ports.[82][83]

When a defective USB-C cable or power source is used, the voltage seen by a USB-C device can be different from the voltage expected by the device. This may result in an overvoltage on the VBUS pin. Also due to the fine pitch of the USB-C receptacle, the VBUS pin from the cable may contact with the CC pin of the USB-C receptacle resulting in a short-to-VBUS electrical issue due to the fact that the VBUS pin is rated up to 20 V while the CC pins are rated up to 5.5 V. To overcome these issues, USB Type-C port protection must be used between a USB-C connector and a USB-C Power Delivery controller.[84]

The USB-C port can be used to connect wired accessories such as headphones.

There are two modes of audio output from devices: digital and analog. There are primarily two types of USB-C audio adapters: active, e.g. those with digital-to-analog converters (DACs), and passive, without electronics.[85][86]

When an active set of USB-C headphones or adapter is used, digital audio is sent through the USB-C port. The conversion by the DAC and amplifier is done inside of the headphones or adapter, instead of on the phone. The sound quality is dependent on the headphones/adapter's DAC. Active adapters with a built-in DAC have near-universal support for devices that output digital and analog audio, adhering to the Audio Device Class 3.0 and Audio Adapter Accessory Mode specifications.

Examples of such active adapters include external USB sound cards and DACs that do not require special drivers,[87] and USB-C to 3.5 mm headphone jack adapters by Apple, Google, Essential, Razer, HTC, and Samsung.[88]

On the other hand, when a passive adapter is used, digital-to-analog conversion is done on the host device and analog audio is sent through the USB-C port. The sound quality is dependent on the phone's onboard DAC. Passive adapters are only compatible with devices that output analog audio, adhering to the Audio Adapter Accessory Mode specification.

In 2016, Benson Leung, an engineer at Google, pointed out that Quick Charge 2.0 and 3.0 technologies developed by Qualcomm are not compatible with the USB-C standard.[89] Qualcomm responded that it is possible to make fast-charge solutions fit the voltage demands of USB-C and that there are no reports of problems; however, it did not address the standard compliance issue at that time.[90] Later in the year, Qualcomm released Quick Charge 4, which it claimed was – as an advancement over previous generations – "USB Type-C and USB PD compliant".[91]

In 2021, the European Commission proposed the use of USB-C as a universal charger.[92][93][94] On 4 October 2022, the European Parliament voted in favor of the new law, Radio Equipment Directive 2021/0291, with 602 votes in favor, 13 against and 8 absentions.[95] The regulation requires that all new mobile phones, tablets, cameras, headphones, headsets, handheld video game consoles, portable speakers, e-readers, keyboards, mice, portable navigation systems, and earbuds sold in the European Union and supporting wired charging, would have to be equipped with a USB-C port and charge with a standard USB-C to USB-C cable by the end of 2024. Additionally, if these devices support fast charging, they must support USB Power Delivery. These regulations will extend to laptops by spring 2026.[96] To comply with these regulations, Apple Inc. replaced its proprietary Lightning connector with USB-C beginning with the iPhone 15 and AirPods Pro second generation, released in 2023.[97]