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Grasping the significance of charge detectors

Posted: 21 Nov 2014 ?? ?Print Version ?Bookmark and Share

Keywords:USB? Battery Charging? BC1.2? SDP? DCP?

Aside from generous helpings of coffee, what helps industry decrease time to market, drive down cost, and focus more of the design cycle on innovation? Hint: standardisation. By defining protocols and operating characteristics, standards have impacted all aspects of technology: device package sizes, pin outs, data and communication interfaces, software drivers, connectors, ESD ratings, environmental compliance, test fixtures. The list goes on and on. The more detailed a specification, the better equipped are developers for defining products that serve the marketplace. If there is any doubt about the value of tightly defined standards, go into any two clothing stores and buy the same size shirt.

The best standards grow with technology. Standards consider and then reflect the increasing complexity of an industry, while maintaining support for already established practices. The USB port is an excellent example of a versatile standard. Originally intended to standardise the connectors on a host computer, the USB specification advanced to allow "On the Go" (USB OTG) electronics to act as either the host or peripheral device.

The specification evolved again with the introduction of the USB Battery Charging (BC) Specification1 to account for the incredible boom of cell phones and other portable devices with a USB port. The USB standard is currently undergoing another evolution with the new USB3.1 specification and the innovative, symmetrical Type-C connector. Because of their ability to "keep up with the Joneses,"2 USB ports are now found wherever chargeable devices are foundwhich is everywhere.

The maintenance of a strong standard such as USB can even influence governmental policy. In June of 2009, the European Commission issued a memo intending to mandate a common charger for every data-enabled mobile phone that uses the Micro-USB connector and draws largely on BC1.2.3 In response, a memorandum of understanding (MoU) was signed by major mobile phone manufacturers including Apple, LG, Samsung, and Sony Ericsson, among others.4

The GSM Association, which organises the Mobile World Congress and spans more than 220 countries, also announced intentions to standardise mobile phone charger connections with a USB connector.5 Both the Korean Telecommunications Technology Association and Chinese Ministry of Industry and Information Technology have released technical requirements for the standardisation of mobile phone charging.6

Even the International Telecommunication Union, a specialised agency within the United Nations, published ITU-T L.1000, its recommendation to adopt a universal charger based on requirements from the GSMA, EU, and Chinese proposals.7 With the updated power-delivery provisions added to USB2.0, the introduction of USB3.1 in 2013, and the new Type-C connector in 2014, the adoption of a standard connector will continue to be influenced heavily by USB standards.

Charger detection and ports in BC1.2
Why are standards committees and governing bodies choosing to standardise around USB connectors and the protocols outlined in BC1.2? Establishing a common standard allows interoperability, optimal performance, and safety among any devices using USB. The specification defines how much power can be supplied by any port, as well as a smart way for portable devices to detect how much power can be drawn. Thus, any portable equipment manufacturer can design their product to be compatible with as many USB ports as possible.

Manufacturers will know how best to utilise each USB port and can anticipate what voltages and currents will be applied by the USB port. Given this knowledge, they can design without the risk of electrical overstress. Finally, the increasing the amount of charging current that a device can use significantly reduces the total charge time required. Consequently, charger detection is an important feature that should be built into all rechargeable devices that incorporate a USB port.

Before discussing the charger detection protocol, it is important to know the differences among available USB ports. A downstream port supports USB 2.0 communication, and a charging port can deliver currents larger than 500mA. The BC1.2 outlines three different port types: a standard downstream port (SDP), dedicated charging port (DCP), and charging downstream port (CDP).

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