Summing Up Circuit Protection for USB 3.0 and USB in Automotive Applications

Following is an excerpt from an article recently published by EECatalog.

 

By VP Pai, ProTek Devices 
As automakers continue to build more and more computing functions into cars, USB will play a big role, whether for data transfer or basic charging.

Version 3.0 of the Universal Serial Bus (USB) specification has been around now since 2008. The technology is now well established across myriad devices requiring high speed data transfer rates. One analyst firm estimated some 70 million USB 3.0 devices shipped in 2011. A further estimate claims this will balloon to more than three billion global USB 3.0 device shipments by 2018. For anyone involved in implementing USB designs, there’s a lot riding on this technology. USB is critical to computing devices that are in turn also critical to everyday business or personal use. Thus proper circuit protection against electrical transients that can break such devices is a must. But, how is it best to implement proper circuit protection for USB 3.0? Also, in general, USB plays a key role in other big applications, like automotive. So, what are some of the key considerations for USB in such an application?

 

Figure 1. TVS Array layout recommendation in USB 3.0+2.0 application

Figure 1. TVS Array layout recommendation in USB 3.0+2.0 application

USB 3.0 Overview
First, a review of the USB 3.0 specification is in order. USB 3.0 offered a generational leap in performance capabilities over USB 2.0. It increased data rates by 10 times. It also expanded transmission lines to three differential pairs (compared to one in the previous 2.0 standard). USB was introduced in 1996 with version 1.0. It provided 1.5Mbit/sec in low-speed (LS) mode and 12Mbit/sec in full-speed (FS) mode. In 2000 USB 2.0 entered the market. The new high-speed (HS) mode then boosted transfer speeds up to 480Mbit/sec. It was downwards compatible to low-speed and full-speed mode.

The USB 2.0 interface is still widely used in consumer electronics. Billions of devices such as camcorders, digital cameras, digital music players, game consoles, DVD/Blue-Ray players and TVs use one or all of these USB standards. It’s also widespread in portable devices such as smartphones and in networking equipment like DSL/router units.

When the USB 3.0 specification was released it demonstrated full USB 2.0 functionality (HS, FS, LS). It also showcased the new separate ultra-high speed data link, called SuperSpeed. The SuperSpeed link works with separate differential data lines for download (host => device, called TX direction). This is also the case for upload in RX direction (device => host). The maximum data rate in SuperSpeed mode is 5Gbit/sec. The combination of USB 2.0 functionality and the new SuperSpeed mode required new cable construction. This new construction had to serve three differential coupled signal lines (TX+/Tx-, RX+/Rx- and D+/D-). The VCC and the GND line complete the cable set. Read the rest at EECatalog.com.

 

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