USB-C

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

USB-C plug for a MacBook

USB-C port (receptacle) on a mobile phone

The 24-pin double-sided connector is slightly larger than the micro-B connector, with a USB-C port measuring 8.4 millimetres (0.33 in) by 2.6 millimetres (0.10 in). Two kinds (genders) of connectors exist, female (receptacle) and male (plug).

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 be ≤2 m for Gen 1 or ≤1 m for Gen 2.[9] The electronic ID chip provides information about product/vendor, cable connectors, USB signalling 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 m. These USB-C cables only support 2.0 speeds and do not support alternate modes.

All USB-C cables must be able to carry a minimum of 3 A current (at 20 V, 60 W) but can also carry high-power 5 A current (at 20 V, 100 W).[10] USB-C to USB-C cables supporting 5A current must contain e-marker chips programmed to identify the cable and its current capabilities. USB Charging ports should also be clearly marked with capable power wattage.[11]

Full-featured USB-C cables that implement USB 3.1 Gen 2 can handle up to 10 Gbit/s data rate at full duplex. They are marked with a SuperSpeed+ (SuperSpeed 10 Gbit/s) logo. There are also cables which can carry only USB 2.0 with up to 480 Mbit/s data rate. There are USB-IF certification programs available for USB-C products and end users are recommended to use USB-IF certified cables.[12]

Devices may be hosts (DFP: downstream-facing port) or peripherals (UFP: upstream-facing port). Some, such as mobile phones, can take either role depending on what kind is detected on the other end. These types of ports are called Dual-Role-Data (DRD) ports, which was known as USB On-The-Go in the previous specification.[13] When two such devices are connected, the roles are randomly assigned but a swap can be commanded from either end, although there are optional path and role detection methods that would allow devices to select a preference for a specific role. Furthermore, dual-role devices that implement USB Power Delivery may independently and dynamically swap data and power roles using the Data Role Swap or Power Role Swap processes. This allows for charge-through hub or docking station applications where the USB-C device acts as a USB data host while acting as a power consumer rather than a source.[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 they can implement the full USB Power Delivery specification using both BMC-coded configuration line and legacy BFSK-coded V_BUS line.[6][11]

Connecting an older device to a host with a USB-C receptacle requires a cable or adapter with a USB-A or USB-B plug or receptacle on one end and a USB-C plug on the other end. Legacy adapters (i.e. adapters with a USB-A or USB-B plug) with a USB-C receptacle are "not defined or allowed" by the specification because they can create "many invalid and potentially unsafe" cable combinations.[14]

A device with a USB-C port may support analog headsets through an audio adapter with a 3.5 mm jack, providing four standard analog audio connections (Left, Right, Microphone, and Ground). 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 signalled through the configuration channel and V_CONN.

An Alternate Mode dedicates some of the physical wires in a USB-C 3.1 cable for direct device-to-host transmission of alternate data protocols. The four high-speed lanes, two side-band pins, and (for dock, detachable device and permanent cable applications only) two USB 2.0 data pins and one configuration pin 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.[3]

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 (release date included in Rev. 1.4)[18]
• Rev 1.4 was published 2019-03-29[18]
• Rev 2.0 was published 2019-08[19]

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"[20]
• 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"[21]
• 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"[22]

The receptacle features four power and four ground pins, two differential pairs for high-speed USB data (though they are connected together on devices), 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.

USB-C receptacle pinout end-on view

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

USB-C plug pinout end-on view

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.[23]

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.[24]

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"[25]

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 are not required to negotiate Alternate Modes and only appear when negotiation fails between the host (source) and device (sink).

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.[26]

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.[27]

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).

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; USB-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.[28]

List of Alternate Mode partner specifications

Logo	Name	Date	Protocol
	DisplayPort Alternate Mode	Published in September 2014	DisplayPort 1.4[29][30]
	Mobile High-Definition Link (MHL) Alternate Mode	Announced in November 2014[31]	MHL 1.0, 2.0, 3.0 and superMHL 1.0[32][33][34][35]
	Thunderbolt Alternate Mode	Announced in June 2015[36]	Thunderbolt 3 (also carries DisplayPort 1.2 or DisplayPort 1.4)[36][37][38][39]
	HDMI Alternate Mode	Announced in September 2016[40]	HDMI 1.4b[41][42][43][44]
	VirtualLink Alternate Mode	Announced in July 2018[45]	VirtualLink 1.0 (not yet standardized)[46]

Other protocols like Ethernet[47] have been proposed.

All Thunderbolt 3 controllers both support "Thunderbolt Alternate Mode" and "DisplayPort Alternate Mode".[48] 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.[49]

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.[29]

Alternate Mode hosts and sinks can be connected with either regular full-featured USB-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 USB-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.[50] 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 0.5 m requires active USB-C cables that are certified and electronically marked for high-speed Thunderbolt 3 transmission, similarly to high-power 5 A cables.[36][39] 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.[51]

USB 3.1 Type-C adapter cable (plug) or adapter (socket)

These cables or adapters contain a valid DisplayPort, HDMI, or MHL plug/socket marked with the logo of the required Alternate Mode, and a USB-C plug with a "trident" SuperSpeed 10 Gbit/s logo on the other end. Cable length should be 0.15 m or less .

Active cables/adapters contain powered ICs to amplify/equalise the signal for extended length cables, or to perform active protocol conversion. The adapters for video Alt Modes may allow conversion from native video stream to other video interface standards (e.g., DisplayPort, HDMI, VGA or DVI).

Using full-featured USB-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.[52]

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, and therefore USB-C is backward compatible with even the oldest USB devices. 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[53] on the CC pins is required, as the source (host) will not supply V_BUS until a connection is detected through the CC pins.

USB Power Delivery uses one of CC1, CC2 pins for power negotiation up to 20 V at 5 A (or whatever less the source can provide). 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 not clobbered.

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 to 10, or 10 to 20 Gbit/s throughput 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 either 1.5 A or 3 A is provided.[54] A third alternative is to establish a Power Delivery 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 type devices connected to it. Other devices may have fallback mode to 2.0, in case the 3.x connection fails.

In the Alternate Mode 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.[30] 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.[30][41] 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.[55]

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

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 14 underlined 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 Rn 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 minimising 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.[56]

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 feature USB-C receptacles. However, further adoption of USB-C is limited by the comparatively high cost of USB-C cables and connectors.[66]

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. 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[67], meaning a user connects their device to the display via USB-C with no other connections required.

Examples of devices that support DisplayPort Alternate Mode over USB-C include: MacBook, Chromebook Pixel, Surface Book 2, Samsung Galaxy TabPro S/Tab S4, iPad Pro (3rd generation), BlackBerry Key2, Essential Phone, HTC 10/U Ultra/U11/U12+, Huawei Mate 10/20/30, LG V20/V30/V40*/V50, OnePlus 7/7T, Razer Phone, ROG Phone/II, Samsung Galaxy S8/S9/S10, Sony Xperia 1/5, Microsoft Lumia 950, HP Elite x3 etc.[68][69][70]

Examples of devices that support high-power charging according to the USB Power Delivery specification include: MacBook, Chromebook Pixel, Surface Book 2, Dell Venue 10 Pro, Lenovo ThinkPad X1, Samsung Galaxy TabPro S, Samsung Galaxy Tab S4, iPad Pro, Nintendo Switch, Nexus 5X/6P, Google Pixel/2/3/4, ROG Phone, BlackBerry Key2, Essential Phone, HTC 10/U Ultra, LG G5/G6, Moto Z, Nokia 8, Razer Phone, Samsung Galaxy S8/S9, Samsung Galaxy Note 8/Note 9,Sony Xperia XZ1/XZ2, Apple iPhone 8/X etc.

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.[71][72][73] There are reported cases of laptops being destroyed due to the use of non-compliant cables.[74]

Some non-compliant cables with a USB-C connector on one end and a legacy USB-A plug or Micro-B receptacle on the other end incorrectly terminate the Configuration Channel (CC) with a 10kΩ pullup to V_BUS instead of the specification mandated 56 kΩ pullup,[75] 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.[76][77]

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 20V while the CC pins are rated up to 5.5V. To overcome these issues, USB Type-C port protection must be used between USB-C connector and USB-C Power Delivery controller.[78]

On devices that have omitted the 3.5 mm audio jack, the USB-C port can be used to connect wired accessories such as headphones.

There are primarily two types of USB-C adapters (active adapters with DACs, passive adapters without DACs) and two modes of audio output from devices (phones without onboard DACs that send out digital audio, phones with onboard DACs that send out analog audio).[79][80]

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/DACs that do not require special drivers,[81] and USB-C to 3.5 mm headphone jack adapters by Apple, Google, Essential, Razer, HTC.[82]

On the other hand, when a passive set of USB-C headphones or adapter is used, analog audio is sent through the USB-C port. The conversion by the DAC and amplifier is done on the phone; the headphones or adapter simply passthrough the signal. The sound quality is dependent on the phone's onboard DAC. Passive adapters without a built-in DAC 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.[83] 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.[84] Later in the year, Qualcomm released Quick Charge 4 technology, which cited – as an advancement over previous generations – "USB Type-C and USB PD compliant".[85]