USB-C port on a smartphone.
|Type||Digital audio/video/data connector/power|
|Designer||USB Implementers Forum|
|Designed||August 11, 2014 (published)|
The USB-C connectors connect to both hosts and devices, replacing various USB-B and USB-A connectors and cables with a standard meant to be future-proof. 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). The connector provides four power/ground pairs, two differential pairs for non-SuperSpeed data (though only one pair is populated in a USB-C cable), four pairs for SuperSpeed data bus (only two pairs are used in USB 3.1 mode), two "sideband use" pins, VCONN +5 V power for active cables, and a configuration pin used for cable orientation detection and dedicated biphase mark code (BMC) configuration data channel.
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 with a USB-C receptacle are "not defined or allowed" by the specification because they can create "many invalid and potentially unsafe" cable combinations.
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) or Dual-Role Port (DRP), which was known as USB On-The-Go in previous specification. 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.
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 VBUS line.
USB-C 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. Electronic ID chip provides information about product/vendor, cable connectors, USB signalling protocol (2.0, gen. 1, gen. 2), passive/active construction, use of VCONN power, available VBUS current, latency, RX/TX directionality, SOP controller mode, and hardware/firmware version .
USB-C 2.0 cables do not have shielded SuperSpeed pairs, sideband use pins, or additional wires for power lines. Increased cable lengths up to 4 m are possible.
All USB-C cables must be able to carry a minimum of 3 A current (up to 60 W @20V) but can also carry high-power 5 A current (up to 100 W). All USB-C to USB-C cables 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.
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.
USB-C plug supports analog headsets through an audio adapter accessory with a 3.5 mm socket providing four standard analog audio signals (Left, Right, Mic, and GND). The audio adapter may optionally include a USB-C pass-through plug to allow 500 mA device charging. The engineering specification states that a 3.5 mm analog headset jack should not replace a USB-C plug.
Analog signals use the USB 2.0 positive differential pair (Dp) and the two side-band use pairs. The presence of the audio accessory is signalled through the configuration channel and VCONN.
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 non-SuperSpeed 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.
|A1||GND||Ground return||B12||GND||Ground return|
|A2||SSTXp1||SuperSpeed differential pair #1, TX, positive||B11||SSRXp1||SuperSpeed differential pair #2, RX, positive|
|A3||SSTXn1||SuperSpeed differential pair #1, TX, negative||B10||SSRXn1||SuperSpeed differential pair #2, RX, negative|
|A4||VBUS||Bus power||B9||VBUS||Bus power|
|A5||CC1||Configuration channel||B8||SBU2||Sideband use (SBU)|
|A6||Dp1||Non-SuperSpeed differential pair, position 1, positive||B7||Dn2||Non-SuperSpeed differential pair, position 2, negative[a]|
|A7||Dn1||Non-SuperSpeed differential pair, position 1, negative||B6||Dp2||Non-SuperSpeed differential pair, position 2, positive[a]|
|A8||SBU1||Sideband use (SBU)||B5||CC2||Configuration channel|
|A9||VBUS||Bus power||B4||VBUS||Bus power|
|A10||SSRXn2||SuperSpeed differential pair #4, RX, negative||B3||SSTXn2||SuperSpeed differential pair #3, TX, negative|
|A11||SSRXp2||SuperSpeed differential pair #4, RX, positive||B2||SSTXp2||SuperSpeed differential pair #3, TX, positive|
|A12||GND||Ground return||B1||GND||Ground return|
|Plug 1, USB Type-C||USB Type-C cable||Plug 2, USB Type-C|
|Shell||Shield||Braid||Braid||Shield||Cable external braid||✓||Shell||Shield|
|GND||Tin-plated||1||GND_PWRrt1||Ground for power return||✓||A1, B12,
|VBUS||Red||2||PWR_VBUS1||VBUS power||✓||A4, B9,
||18||PWR_VCONN||VCONN power, for active cables[b]||✓||B5||VCONN|
|A6||Dp1||White||4||UTP_Dp[c]||Unshielded twisted pair, positive||✓||A6||Dp1|
|A7||Dn1||Green||5||UTP_Dn[c]||Unshielded twisted pair, negative||✓||A7||Dn1|
|A8||SBU1||Red||14||SBU_A||Sideband use A||✗||B8||SBU2|
|B8||SBU2||Black||15||SBU_B||Sideband use B||✗||A8||SBU1|
|A2||SSTXp1||Yellow[d]||6||SDPp1||Shielded differential pair #1, positive||✗||B11||SSRXp1|
|A3||SSTXn1||Brown[d]||7||SDPn1||Shielded differential pair #1, negative||✗||B10||SSRXn1|
|B11||SSRXp1||Green[d]||8||SDPp2||Shielded differential pair #2, positive||✗||A2||SSTXp1|
|B10||SSRXn1||Orange[d]||9||SDPn2||Shielded differential pair #2, negative||✗||A3||SSTXn1|
|B2||SSTXp2||White[d]||10||SDPp3||Shielded differential pair #3, positive||✗||A11||SSRXp2|
|B3||SSTXn2||Black[d]||11||SDPn3||Shielded differential pair #3, negative||✗||A10||SSRXn2|
|A11||SSRXp2||Red[d]||12||SDPp4||Shielded differential pair #4, positive||✗||B2||SSTXp2|
|A10||SSRXn2||Blue[d]||13||SDPn4||Shielded differential pair #4, negative||✗||B3||SSTXn2|
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).
While it is not necessary for USB-C compliant devices to implement USB Power Delivery, for USB-C interfaces that have implemented the USB Power Delivery protocol (i.e. beside those solely acting as a source for power or as a sink to receive power) it is possible for the connector to support DRP (Dual Role Power), which would allow the port to act as both a source to supply electricity and as a sink to be recharged.
As of 2016 four system-defined Alternate Mode partner specifications exist. Additionally, vendors may support proprietary modes for use in dock solutions.
|DisplayPort Alternate Mode||Published in September 2014||DisplayPort 1.4|
|Mobile High-Definition Link (MHL) Alternate Mode||Announced in November 2014||MHL 1.0, 2.0, 3.0 and superMHL 1.0|
|Thunderbolt Alternate Mode||Announced in June 2015||Thunderbolt 3 (includes DisplayPort 1.2 Alternate Mode)|
|HDMI Alternate Mode||Announced in September 2016||HDMI 1.4b|
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.
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.
Alternate Mode hosts and sinks can be connected with either regular full-featured USB-C cables, or converter cables/adapters:
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.
|Mode||USB 3.1 Type-C cable[nb 1]||Adapter cable or adapter||Construction|
|USB[nb 2]||DisplayPort||Thunderbolt||superMHL||HDMI||HDMI||DVI-D||Component video|
|3.1||1.2||1.4||20 Gbit/s||40 Gbit/s||1.4b||1.4b||2.0b||single-link||dual-link||(YPbPr, VGA/DVI-A)|
|DisplayPort||Yes||Yes||Does not appear||No||Passive|
|Does not appear||Optional||Yes||Yes||Yes||Active|
|Thunderbolt||Yes ||Yes ||Does not appear||Yes||Yes[nb 3]||Does not appear||No||Passive|
|Does not appear||Optional||Optional||Yes||Yes||Yes||Yes||Active|
|MHL||Yes||Does not appear||Yes||Does not appear||Yes||No||Yes||No||No||Passive|
|Does not appear||Optional||Does not appear||Yes||Does not appear||Yes||Active|
|HDMI||Does not appear||Yes||Yes||No||Yes||No||No||Passive|
|Optional||Does not appear||Yes||Active|
The diagrams below, depict the pins of a USB-C socket in different use cases.
A simple USB 2.0/1.1 device mates using one pair of D+/D− pins. Hence, it does not require any connection management circuitry, and therefore USB-C is backward compatible with even the oldest USB devices. VBUS and GND provide 5 V up to 500 mA of power.
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.
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 20 Gbps throughput. One of the CC pins is used to negotiate the mode.
VBUS 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 up to 3 A is provided. A third alternative is to establish a Power Delivery contract.
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. 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. 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.
The purpose of this mode is to replace the 3.5 mm headphone jack, from devices like smartphones and tablets, with the thinner USB-C jack. It is supposed to operate only with an adaptor: USB-C plug to headphone jack, so manufacturers are not supposed to market analog headsets with a USB-C plug instead of a headphone plug. This mode is totally separate from digital audio through USB, which typically would use the USB 2.0 mode.
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.
This mode also allows concurrent charging of a device exposing the analog audio interface (through VBUS and GND), however only at 5 V and 500 mA, as CC pins are unavailable for any negotiation.
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.
Currently, DisplayPort is the most widely implemented alternate mode, and is used to provide video output on devices such as the MacBook, Chromebook Pixel, HTC U11, Samsung Galaxy S8, Samsung Galaxy TabPro S, Microsoft Lumia 950, and Nintendo Switch. 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.
Examples of devices that support high-power charging according to the USB Power Delivery specification include the MacBook, Chromebook Pixel, Dell Venue 10 Pro, Lenovo ThinkPad X1, Nintendo Switch, Nexus 5X, Nexus 6P, Google Pixel, Samsung Galaxy TabPro S, Samsung Galaxy S8, Samsung Galaxy Note 8, LG G6, and Moto Z.
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. There are reported cases of laptops being destroyed due to the use of non-compliant cables.
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 VBUS instead of the specification mandated 56kΩ pullup, 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.
As described above, it is possible to use the Audio Adapter Accessory Mode to provide analog audio signal connection over USB-C plug, however it is not mandatory to support the mode. The USB-C port on some devices might only support the digital audio output mode, which make it necessary to use a digital-to-analog converter in order to send audio output toward earphone or speakers that can only accept analog input.
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. 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. 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".
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