USB-C: The New Gorilla In The Room

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It’s hard to escape the excitement around the new USB Type C standard and its siblings: USB 3.1 and the USB Power Delivery specification. But what is it and why should you care? Here’s our take.

The Road to USB 3.1 and USB-C

The Universal Serial Bus (USB) specification dates back over 20 years to 1994, when development was started by a group of seven companies including Intel and Microsoft. The current board of directors additionally includes HP, Renesas and STMicroelectronics, collectively known as the USB Implementers Forum (USB-IF).

USB 1.1, introduced in 1998, was the first widely adopted version. The data transfer rate has steadily increased in successive releases, as can be seen in Table 1.

 

Version

Release Date

Speed

1.1

August 1998

Low Speed (1.5Mbps), Full Speed (12Mbps)

2.0

April 2000

High Speed (480Mbps)

3.0

November 2008

SuperSpeed (5Gbps)

3.1

July 2013

SuperSpeed+ (10Gbps)

 

Table 1: USB Releases (Source: Wikipedia)

Before USB-C, there were three basic kinds or sizes related to the USB connectors and types of established connection: the older “standard” size, in its USB 1.1/2.0 and USB 3.0 variants (for example, on USB flash drives), the “mini” size (primarily for the B connector end, such as on many cameras), and the “micro” size, in its USB 1.1/2.0 and USB 3.0 variants (for example, on most current cellphones).

Prior USB standards specify a different kind of connector (an A-type or a B-type) in order to prevent electrical overloads and damaged equipment; only the A-type socket provides power. Each of the different “sizes” requires four different connectors; USB cables have the A-type and B-type plugs, and the corresponding receptacles are on the computer or electronic device. In practice, the A-type connector is usually the full size, and the B-type side can vary as needed.

USB-C Specification

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Figure 1: USB Type-A and USB Type-C comparison. (Source: AliExpress)

The latest USB connector and cable specification is USB-C, which brings several important advances to USB interconnection. Although it’s much thinner than the Type-A (2.4 mm vs. 4.5 mm), as can be seen in Figure 1, it contains 24 pins vs. 5 in earlier versions. The connector is also reversible and can be plugged into a receptacle in either direction without issue.

USB-C is intended to be a common standard for both hosts and receptacles, replacing various Type-A and Type-B connectors. It’s meant to be “future-proof,” with capability for future expansion; it also accommodates other standards with its Alternate Mode, discussed below.

Given the ubiquity of previous versions of USB and the prospects going forward, it has been referred to as “One Standard To Rule Them All,” and for good reason.

What USB-C Is, And Is Not

USB-C is a connector and cable specification and should be distinguished from two other related specifications: USB 3.1 and the USB Power Delivery specification.

If a product features USB-C, that doesn’t necessarily mean that it supports either USB 3.1 or USB Power Delivery. So, for example, a USB-C cable and connector can be used in a standard USB 2.0 system that supports neither USB 3.1 nor USB PD.

This makes good sense: a flash drive for example, may have a Type-A connector and only support USB 2.0, but still needs to plug into a laptop’s USB-C receptacle. But don’t worry, there are numerous adapter cables available.

USB-C Pinout

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Figure 2: USB-C pinout. (Source: Arstechnica)

Figure 2 shows the USB-C pinout. It has five distinct sections:

1)      4 VBUS/GND power and ground pairs

2)      High-Speed Data Path: 4 differential pairs for the USB 3.1 SuperSpeed mode, if implemented. SuperSpeed uses full-duplex communication.

3)      2 USB 2.0 D+/D- pairs:  required to implement USB 2.0 functionality (only 1 pair used)

4)      2 sideband pins: available for Alternate Mode use

5)      2 CC plug configuration pins: used to detect cable orientation and implement the USB Power Delivery Specification

 

How does USB-C achieve connector reversibility? The pins are rotationally symmetrical. The power pins VBUS and GND always match; flipping the connector connects the TX1 pair to TX2, the RX1 pair to RX2, and so on. The two CC pins are used to determine the connector orientation upon insertion into the receptacle; the host device then changes the receptacle pinout accordingly.

USB-C Alternate Mode

Alternate Mode dedicates some of the physical wires in the USB Type-C cable for direct device-to-host transmission of alternate data protocols. The four high-speed lanes, two sideband (SBU) pins, and—for dock, detachable device and permanent cable applications only—two USB 2.0 pins and one configuration pin can be used for Alternate Mode transmission. The modes are configured using vendor-defined messages (VDMs) through the CC pins.

For example, DisplayPort is a popular interface standard for connecting a video source to a display device such as a computer monitor. Its controlling authority VESA and the USB-IF have issued the “DisplayPort Alt Mode for USB Type-C Standard,” which governs its use over USB-C. The DP Alt Mode standard will allow standard USB Type-C connectors and cables to carry native DisplayPort signals by re-purposing up to four SuperSpeed pins (two TX/RX pairs). The Type-C secondary bus pins can also be used for the DisplayPort AUX channel, which is normally used by DisplayPort devices to carry additional non-video data such as audio or touchscreen information.

The USB-C Cable Specification

The USB-C connector can be used with a traditional straight-through cable; there is also a specification for a full-featured USB Type-C cable—an active, electronically marked cable that contains a chip with an ID function based on the configuration data channel and VDMs from the USB Power Delivery 2.0 specification.

USB Type-C devices also support power currents of 1.5 A and 3.0 A over the 5 V power bus in addition to the baseline 900 mA; devices can either negotiate increased USB current through the configuration line, or they can support the full Power Delivery specification.

USB System Design

Many different components are needed to accomplish an efficient, robust and fully compliant USB Type-C design, as illustrated in Figure 3. Some of the blocks are:

Load switches: automatically isolate the system from a faulty source of load. Look for added features like under/over-voltage protection, reverse-current protection, over-temperature protection, and programmable current limits.

USB PD PHY: if your system also complies with the USB Power Delivery specification, a combination controller and protocol responder is required to establish link operation and deliver power.

US PD microcontroller: Type-C functionality requires complex decision-making so a microcontroller and specialized firmware are necessary.

High-performance switches: provide a signal multiplex or de-multiplex function redirecting transmitted signals to the same or different connection ports. These functions can be combined into a cross-point switch to support Alternate Mode functions.

Signal conditioners: regenerate the USB signal, remove jitter, extend channel transmission and reduce the bit error rate (BER).

Interface protection: provides ESD protection, along with Common Mode filters that help eliminate interference from wireless technologies such GSM, LTE and Wi-Fi.

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Figure 3: System solution for USB Type-C connector. (Source: NXP)

The Arrow and NXP partnership

Arrow Electronics is a giant in the distribution space with 2014 sales of $22.8 billion. As a Fortune 150 company with 17,000 employees and a global network of more than 460 locations in 58 countries, we bring technology solutions to customers worldwide, and provide specialized services and expertise across the product lifecycle.

We’re expert at bringing technology to market, with special events, technology forums, custom boards, and more to help our customers become familiar with disruptive technologies such as USB-C. But we go above and beyond—combining technologies from multiple suppliers to put together full solutions so you can get to market faster.

As a longtime leader in USB systems, NXP has been a key part of the USB-C definition team and has the most complete range of products and system solutions for this exciting new market. NXP products for USB-C run the gamut and include ARM-based MCUs with USB-PD firmware; signal conditioners to improve transmission distances and reduce BER; N-channel power switches that automatically isolate a system from a faulty source or load; and the new PUSB3TB6, a very small electrostatic discharge (ESD) protection device designed to protect six ultra-high-speed data lines.

Given this depth and breadth of experience, it is only natural that Arrow and NXP should partner up to make your transition to USB-C as quick and painless as possible. We’re still finalizing the details, but look for unique NXP-Arrow USB-C solutions in the near future.

Conclusion

USB-C, USB 3.1 and USB PD together form the path forward for USB. The innovative aspects of the complete system—the reversible connector, the increased speed, and the new PD format—certainly introduce specific design challenges, as well as new requirements for protecting signals and ensuring performance in all kinds of conditions.

Unlike some other standards that promised much only to fizzle in the marketplace, it’s not an issue of whether USB-C will be adopted, but how quickly. New products are already in stores. The only question really is how long before it’s the only standard you need.

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