What is USB Type-C?

This is a basic explanation of USB Type-C. It also describes the differences from traditional USB-A and USB micro-B. With 24 pin assignments, USB Type-C is a new standard connector that is reversible and can be used for both data communication and power delivery.

What is USB Type-C?

USB Type-C refers to a new connector standard for USB. It is commonly referred to as USB Type-C™ or USB-C™, which are registered trademarks of the USB Implementers Forum, a nonprofit organization responsible for USB specification development.

USB Type-C was officially introduced in 2014. Recently, it has been adopted by PC manufacturers including Apple, and USB-C AC adapters are increasingly seen in everyday life. For example, the recently announced iPhone 11 Pro and iPhone 11 Pro Max include an 18W USB-C compatible adapter.

Power supply and data transfer at the same time

The key feature of the USB Type-C connector is that it allows simultaneous power delivery and data transfer. It is expected to become more widespread as it is used in various products and standards such as USB Power Delivery (PD) and Quick Charge.

Recently, Apple incorporated USB-C in the new iPhone 15, enabling charging from an iPad Pro to devices like an iPhone, which has garnered attention. This could indicate a trend of USB-C eventually replacing Thunderbolt.

Even faster data transfer than previous generations

USB-C supports USB 3.1 Gen 2, which offers about double the theoretical speed of USB 3.0, reaching 10 Gbps. This makes it ideal for high-speed data transfer and taking full advantage of USB-PD features. (Please note, not all USB Type-C connectors support USB 3.1.)

Summary of USB standards history (From 1.0 to USB4)

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

Connector landscape before USB (pre-1996)

Before USB, PC manufacturers used various proprietary connectors for data transfer such as serial ports, parallel ports, special plugs, connectors, and cables, often requiring special drivers or expansion cards. These methods were slow—parallel ports topped out at 100 KB/s and serial ports at 450 Kbps. Connecting new devices often required system shutdowns or reboots.

USB development began in 1994 by the USB Implementers Forum (USB-IF). Early versions USB 0.8 and 0.9 were pre-releases and not commercially launched. USB 0.99 was announced in 1995 but also not deployed. However, these developments paved the way for standardized technologies.

Introduction of USB 1.0 (1996)

In early 1996, USB 1.0 was released with low-speed (1.5 Mbps) and full-speed (12 Mbps) modes. It featured automatic configuration and hot-swapping. Despite being innovative, USB 1.0 was not widely adopted initially due to limited device availability.

USB 1.1 (1998)

USB 1.1, a revised version of 1.0, was released in 1998. Although data speeds remained the same, it supported lower bandwidth devices. It led PC makers to drop serial and parallel ports, boosting USB's market appeal. Type A (rectangular) and Type B (square) connectors became the standard.

USB 2.0 (2000)

In April 2000, USB 2.0 was launched with data transfer speeds up to 480 Mbps (actual ~280 Mbps). It enhanced power supply features and supported plug-and-play for multimedia and storage. USB On-the-Go allowed direct transfer between devices, and was compatible with connectors including Type A, B, C, mini, and micro variants. USB flash drives also debuted, fueling USB’s popularity.

Wireless USB and USB Micro overview (2005)

Wireless USB (W-USB), introduced in 2005, offered short-range wireless connectivity at 480 Mbps over 10 meters but is now obsolete. The 2007 micro USB connector, smaller than mini-B, enabled fast charging and data transfer for Android devices. It was a physical connector standard, not a communication one, and supported mobile device integration.

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

USB 3.0 (now USB 3.2 Gen 1) was introduced in 2008 to meet growing storage and bandwidth demands. It provided up to 5 Gbps (actual ~3 Gbps) and full-duplex data transfer. In 2017, USB 3.2 replaced 3.0 and 3.1, introducing USB 3.2 Gen 2x2 with 20 Gbps speeds, and debuting the reversible USB Type-C connector.

This marked the introduction of the Type-C connector.

Latest standard: USB4.0 (2019–)

The latest standard is USB4.

Released in 2019, USB 4.0 is based on the Thunderbolt 3 protocol and supports up to 40 Gbps data transfer and 240W power delivery. It uses existing Type-C connectors and is backward-compatible with USB 2.0 and 3.2 (with possible speed limitations). Intelligent power delivery allows bi-directional flow of up to 240W.

(USB history timeline)

Comparing past connector shapes

The shape of the USB Type-C connector closely resembles the size of Micro-USB and is compact with an oval design. The leftmost connector in the image is likely the familiar USB Type-A. Unlike Type-A, which is not reversible and often inserted wrongly, USB Type-C is reversible and easier to use.

About USB Type-C pin assignment

USB Type-C pin assignment is well designed

The pinout of Type-C is shown in the following configuration:

The data lanes are TX1+, TX1-, RX1+, RX1-, RX2-, RX2+, TX2-, TX2+. The central D+/D- pair is for USB 2.0 data, CC1/CC2 for connection/configuration detection, Vbus for power, and GND for grounding. The pinout ensures signal pairing even if the connector is inserted upside down.

Pin assignment depending on mode or use

USB 2.0/1.1 devices

Pin usage for USB 2.0/1.1 devices is as follows:

VBUS and GND support up to 5V 500mA. D+/D- pins are used for data. A pull-down resistor (Rd) is needed on the CC pin when connecting a USB-C host to 2.0/1.1 devices.

USB 3.0/3.1/3.2 devices

Pin usage for USB 3.0/3.1/3.2 devices is as follows:

These modes use up to four TX/RX high-speed lanes for throughput between 5 to 20 Gbps. One CC pin is used for mode negotiation. USB 3.1 supports transmission up to 5V 900mA or even 5V 3A.

Ideal for compact and slim devices

MicroUSB and Mini-USB emerged due to the need for smaller connectors as devices became thinner. USB-C is roughly one-third the size of USB-A, making it suitable for compact and slim devices.

Alternate mode support simplifies cable management

Audio/video connectors like HDMI, DisplayPort, VGA, and Thunderbolt 3 each have their own standards. USB-C supports all of them through Alternate Mode, enabling simultaneous power and data/video communication.

In the example above: left port charges a smartwatch via USB-A, center port outputs to a monitor via HDMI, and right port charges a notebook PC and smartwatch—all consolidated by USB-C. Three cables become one.

Alternate Mode uses dedicated lanes from USB 3.1 cables, including four high-speed lanes, two sideband pins, two USB 2.0 data pins, and one configuration pin. It is activated through vendor-defined messages (VDM) via the configuration channel.

In 2018, the Alternate Mode Partner Specification was defined across five systems. This is an optional feature, and not all USB-C devices are required to support it. The USB-IF works with partners to ensure correct labeling of ports with logos.

Alternate Mode pin usage:

In Alternate Mode, SBU1 and SBU2 act as low-speed links while up to four high-speed lanes are used directionally. If only two high-speed lanes are occupied, USB 3.0/3.1 communication can still be established. Pin CC is for negotiation and USB 2.0 uses D+/D- for signal.

Audio accessory mode

Devices with USB-C may include optional adapters for 3.5mm analog audio and support 500mA charging. This enables simultaneous charging and analog audio playback via USB-C. Eventually, 3.5mm jacks may disappear altogether, with USB-C becoming standard for audio.

Summary

What differentiates USB-C from familiar connectors like USB-A or USB Micro-B? Here's a summary:

• Reversible design (no top/bottom orientation simplifies insertion).
• Higher power supply (5.0V/1.5A to 5.0V/3A; up to 100W with PD at 20V/5A).
• Increased pin count (from 4–5 pins to 24 pins).
• Usable on both host and device sides.
• High-speed data transfer.
• Supports video output.

USB-C photos and diagrams

We hope it's clear that USB-C offers improved convenience compared to previous standards.

Our company manufactures and customizes adapters with USB-C terminals. Please feel free to contact us.

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