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Selecting the right USB version for your app

Posted: 04 May 2012 ?? ?Print Version ?Bookmark and Share

Keywords:SuperSpeed USB? PC interfaces? I/O? On-the-Go?

Several new and different "versions" of USB have been released in the past few years. In this article, I discuss how they have been deployed in the market. Also, I address SuperSpeed USB (USB 3.0) and its impact on the USB market. I would also be remiss if I do not address ThunderboltTechnology as well and its impact on PC interfaces moving toward the future. We will close this article by discussing some recently announced new initiatives from the USB-IF aimed to enhance the end consumer experience with USB.

USB 2.0 revisited
As Brian O'Rourke of In-Stat commented many years ago, USB is the most successful I/O in the history of the PC. This remains the case today after over 15 years of life. As discussed in 2007, USB 2.0 is a specification that defines three speed modes: low-speed, full-speed, and high-speed.

All three speeds are still used extensively today for new products. Low-speed continues to be used for most human-interface devices such as keyboards and mice. Full speed still is used in many industrial, medical, and industrial control applications. Finally, high-speed has been the main interface of choice for most of the new content-rich consumer products such as portable media players, digital still cameras, and the ubiquitous flash drives that I do not know how we ever lived without!

USB high-speed products will be the interface that is most impacted by SuperSpeed USB as even greater content is stored and the desire to enhance the sync-and-go experience of the consumer, but more on that later.

The second most significant development (the release of the USB 3.0 specification being the most significant) in the USB market since my original articles is the use of the USB connector for charging battery-powered portable-consumer products. When first released, the USB specification did not really take into account the potential desire to charge batteries with VBUS that is defined as 5V and 500 mA for a host port or a self-powered hub port.

The USB-IF has released a battery-charging addition to the USB specification with the goal of helping to improve the user experience when it comes to charging their devices via a standard USB connection. The battery charging (BC) specification defined a mechanism for the device to negotiate for additional power, if it, as well as the host (hub) port are BC compliant. On the host side, the specification defines three types of ports to support charging:

Standard downstream port (SDP):
???This is the same as any pre-BC downstream port
???Provides up to 100 mA during enumeration
???Provides up to 500 mA after enumeration for charging with data transfer

Charging downstream port (CDP):
???Provides up to 100 mA during enumeration
???Provides up to 1.5A for charging with data transfer

Dedicated charging port (DCP):
???Referred to as wall adaptor charging mode
???Provides up to 1.5A for charging but with no data transfer
???Provides charging even if the host is turned off

In addition to the USB-IF BC specification, there have been other initiatives related to battery charging. The Chinese government has mandated the mobile phones must use a micro-USB receptacle for charging. This is called Chinese Telecom Mode (Standard YD/T 1591-2009) as it relates to battery charging. The mandate is intended to eliminate the need for phone providers to ship a new charger (with proprietary connectors) with every phone.

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