What is USB Type-C?

This provides a basic explanation of USB Type-C. It also describes the differences from conventional USB-A and USB micro-B. USB Type-C, which has a 24-pin assignment, is a new standard connector that is reversible and supports both data communication and power delivery.

What is USB Type-C?

USB Type-C is a new connector standard in the USB specification. It is also referred to as USB Type-C™ or USB-C™, and these names are registered trademarks of the USB Implementers Forum, the non-profit organization that develops USB specifications.

USB Type-C was officially announced in 2014. In recent years, PC manufacturers including Apple have adopted USB-C ports, and opportunities to see USB-C AC/DC Power Adapter in everyday life have increased. The recently announced iPhone 11 Pro and iPhone 11 Pro Max come with an 18W USB-C compatible adapter.

Supports power delivery and data transfer simultaneously

The appeal of the USB Type-C connector is that it enables simultaneous power delivery and data communication. It is expected to become even more widespread as it is adopted in various Products and standards such as USB Power Delivery (PD) and Quick Charge.

The recently announced iPhone 15 by Apple has adopted USB-C, making it possible to charge other devices such as an iPad Pro from the iPhone, which has attracted significant attention. This may signal a future shift from Thunderbolt to USB-C.

Enables even faster data transfer than before

Compared to conventional USB 3.0, USB-C compatible with USB 3.1 Gen 2 allows data transfer at approximately twice the speed (theoretical value of 10 Gbps). This makes it a connector that fully leverages high-speed data transfer and the features of USB-PD. (Note that not all USB Type-C connectors support USB 3.1.)

Summary of USB Standard History (from 1.0 to USB4)

Let’s take a look at the history of USB.

Connector situation before USB adoption (before 1996)

Before USB was introduced, PC manufacturers used various proprietary connection methods for data transfer. These included serial ports, parallel ports, special plugs, connectors, and cables, often requiring dedicated drivers or expansion cards. Data transfer speeds were slow, limited to a maximum of 100 kilobytes per second for parallel ports and 450 kilobits per second for serial ports. Additionally, connecting new devices frequently required shutting down or restarting the computer.

Initial USB development began in 1994 by the USB Implementers Forum (USB-IF). The first versions were USB 0.8 and USB 0.9, released as pre-releases but never commercially launched. In 1995, USB 0.99 was announced, but it also never reached the market. These developments were important steps toward later industry standardization.

USB 1.0 debut (1996)

USB 1.0 debuted in early 1996 as the first official USB version. It supported data transfer speeds of 1.5 Mbps in low-speed mode and 12 Mbps in full-speed mode. USB 1.0 featured automatic configuration, eliminating the need for users to manually adjust device settings. It supported hot swapping, so restarting the host computer was unnecessary when replacing devices. However, despite its innovation, adoption was limited and compatible devices were scarce.

USB 1.1 (1998)

In 1998, USB 1.1, an improved version of USB 1.0, was released. While data transfer speeds remained the same, it enabled operation at lower speeds for low-bandwidth devices. As PC manufacturers phased out serial and parallel ports, USB gained broader market attention. Standard connector shapes such as rectangular Type A and square Type B were used.

USB 2.0 (2000)

USB 2.0 was introduced in April 2000 with a maximum data transfer speed of 480 Mbps (actual speed around 280 Mbps). Enhanced plug-and-play support and improved power supply capabilities promoted business use, especially for multimedia and storage devices. The USB On-the-Go function enabled direct data exchange between devices. It was compatible with USB Type A, B, C, and mini/micro A and B connectors. In 2000, the first USB flash drive appeared, further accelerating USB adoption.

Overview of Wireless USB and USB Micro (2005)

Wireless USB (W-USB), announced in 2005, was a short-range wireless network standard supporting 480 Mbps within a 10-meter range, but it is no longer in use. Meanwhile, the USB Micro connector introduced in 2007 was smaller than the Mini-B connector and provided fast charging and data transfer for Android devices. It is a physical connection standard, distinct from the USB communication standard, and contributed to improved connectivity for mobile devices.

USB-C 3.0/3.1/3.2 and the emergence of the Type-C connector (2008-2017)

USB 3.0 (now known as USB 3.2 Gen 1) was released in 2008 to meet growing demand for digital storage and bandwidth, offering transfer speeds up to 5 Gbps (actual around 3 Gbps) with bidirectional data transfer. In 2017, USB 3.2 replaced USB 3.0 and 3.1, introducing USB 3.2 Gen 2x2 with speeds up to 20 Gbps. The USB Type-C connector was also introduced, enabling compact, reversible connections.

This marked the arrival of the Type-C connector.

Latest standard USB4 (2019-)

The latest USB4 standard is now available.

USB 4.0, released in 2019, is based on the Thunderbolt 3 protocol and supports data transfer speeds up to 40 Gbps and power delivery up to 240 W. It uses the existing Type-C connector and is backward compatible with USB 2.0 and 3.2, although speeds may be reduced. Intelligent power delivery enables up to 240 W of bidirectional power flow.

(USB history timeline)

Comparing with conventional connector shapes

From this, you can see that the USB Type-C connector is closest in size to Micro-USB and has a compact, oval shape. The connector on the far left is likely the most familiar to general users: USB Type-A.
USB Type-A is not reversible, and many people have experienced inserting it the wrong way. USB Type-C is reversible, eliminating that inconvenience.

About USB Type-C pin assignment

USB Type-C pin assignment features a clever layout

The Type-C pin assignment is arranged as follows:

There are eight data lanes (TX1+, TX1-, RX1+, RX1-, RX2-, RX2+, TX2-, TX2+). The central D+ and D- are for USB 2.0 data communication. CC1 and CC2 are used for connection detection and configuration, Vbus supplies bus power, and GND is ground. The pin layout is designed so that even if connected upside down, the appropriate signal pins will align correctly.

Comparison of pin assignments by mode and usage

For USB 2.0/1.1

For USB 2.0/1.1 devices, the following lanes are used:

VBUS and GND can supply up to 5V/500mA, using one pair of D+ and D- pins. To connect a USB 2.0/1.1 device to a USB-C host, Rd must be used on the CC pin.

For USB 3.0/3.1/3.2

In USB 3.0/3.1/3.2 mode, the following lanes are used:

Up to four TX/RX high-speed links are used to achieve throughput from 5 to 20 Gbps. One CC pin is used for mode negotiation. In USB 3.1, up to 5V/900mA can be supplied via GND and Vbus, and 5V/3A is also possible.

USB-C is ideal for compact and thin devices

MicroUSB and Mini-USB emerged after USB Type-A because devices became smaller and thinner, making the large USB-A connector difficult to accommodate.

USB-C is about one-third the size of conventional USB Type-A, making it suitable for compact and slim devices.

Alternate Mode simplifies cabling

Various connectors such as HDMI, DisplayPort, VGA, and Thunderbolt 3 are used for video and audio output. USB-C supports an Alternate Mode that accommodates these signals, enabling both power delivery and data/video transmission.

In the example above, the left port charges a smartwatch via USB-A, the center port outputs video to a monitor via HDMI, and the right port supplies power to a smartwatch and laptop. Instead of three separate connections to the laptop, only one is required.

In Alternate Mode, certain lines of a USB-C 3.1 cable are dedicated to transmitting alternate protocol signals from device to host. Four high-speed lanes, two sideband pins, two USB 2.0 data pins, and one configuration pin can be used for Alternate Mode transmission. This mode is configured through the configuration channel using Vendor Defined Messages (VDM).

In 2018, the Alternate Mode Partner specification was defined by five systems. Alternate Mode is optional, and supporting specific alternate modes is not mandatory for USB-C devices. USB-IF works with partners to ensure proper port labeling.

The lanes used in Alternate Mode are shown below:

In Alternate Mode, SBU1 and SBU2 serve as low-speed links, and up to four high-speed links are used as needed. If two high-speed links are unused, a USB 3.0/3.1 link can be established. The CC pin is used for negotiation, and USB 2.0 signals can be obtained from the D+ and D- pins.

Audio Accessory Mode

Some USB-C devices optionally include a USB-C conversion port to support 3.5 mm analog headset adapters while enabling up to 500 mA device charging. This allows users to listen to music with an analog headset while charging a smartphone. In the future, listening to music via USB-C may become standard, potentially eliminating the 3.5 mm jack from smartphones.

Summary

What are the differences compared to commonly known USB-A and USB Micro-B?

• Reversible design (no difference between top and bottom, making insertion easier)
• Higher power supply (from 5.0V/1.5A to 5.0V/3A; up to 100W (20V/5A) with PD support)
• Increased pin count (from 4-5 pins to 24 pins)
• Can be configured as Type-C on both host and device sides
• High-speed data transfer
• Supports video output

Photos and drawings of USB-C

Compared to conventional standards, you can see that usability has significantly improved.

We also manufacture and offer custom support for adapters equipped with USB-C connectors. Please feel free to contact us.

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