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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?

Designers looking for a charger detector to drop into existing designs with minimal additional component count and board space will want the MAX14576/MAX14636/MAX14637 family of devices. This class of charger detector is powered directly from the USB VBUS line, so there is no need to add an additional supply. They feature internal SPST switches that are open when performing charger detection and closed when USB data communication is enabled.

Each device has an open-drain I/O to signal whether charging is allowed and the status of the data switches. Some charger detector versions have built-in Apple charger detection in addition to the BC1.2 compliant port detection. Figure 3 shows an example detection circuit that handles the detection protocol. Fewer main processor resources are required and no major modifications need to be made to an existing design.

 MAX14636 charger detector

Figure 3: MAX14636 charger detector block diagram.

Over the last few years, smartphones took the world by storm. One of the major forces driving this sleek technology is form factor. As the list of features continues to increase while overall sizes are shrinking, careful planning and integrated solutions must be implemented to achieve the target shrinking specifications. Take, for example, a mobile phone that uses a single connector for charging; connecting to a PC; connecting to external accessories; or audio playback. To accomplish all of these tasks in a compact manner, system designers can opt to use a charger detection IC such as the MAX14656 (figure 4).

 MAX14656 charger detector

Figure 4: A smartphone application using the MAX14656 charger detector.

This universal charger detection circuitry automatically distinguishes between different BC1.2-compliant ports and supports detection of most of the Apple proprietary chargers (e.g., 500mA, 1A, 2.1A). This device also has integrated DPDT switches, which allows the D+ and D- lines to be shared by a Hi-Speed USB transceiver, audio outputs, or even an internal UART. Using an I2C interface, the embedded processor reads whether a charger has been attached and configures the internal switches for the appropriate mode. When you consider the built-in OVP on the VBUS pin, the ESD protection on the data lines, and the 1.65mm x 1.65mm footprint, this single charger detector adds considerable versatility in a single connector for space-constrained designs.

The promise for portable electronic devices
Charger detection technology is so versatile because the basic charger detector functions can be coupled with a variety of other features to provide highly integrated circuits for manufacturers of portable electronics. Other solutions combine charger detection with Li+ battery-charging control in a single package. Some combine charger detection with USB self-enumeration. Today's newest charger detector chips autonomously monitor the battery charge cycle in accordance with BC1.2, instead of tasking the embedded processor with manually adjusting the total current drawn for the time periods defined in the specification.

When you combine the charger detection and battery charging functions, you have smart battery switch control. This technology automatically switches from battery power to charger power when a charger is present. Consequently, some charger detector chips can both charge a battery and provide full-load current. Devices that do this also support thermal current regulation, which protects against dangerously high temperatures that result from simultaneously charging the battery and providing current to the load. By integrating charger detection and battery charging, the system designer can focus more on the end application and worry less about charging concerns.

Meanwhile, the USB BC1.2 specification continues to drive the electronics industry by providing a standard on which manufacturers can build upon. The large number of BC1.2-compliant chargers available today is only expected to multiply in volume. That fact alone makes incorporating a USB connector into a portable device an attractive option. With the use of charger detection ICs, the USB connector on a portable device becomes a versatile component. The built-in BC1.2 compliance keeps the implementation clean and simple to use. Whether designing a compact and portable product, the wealth of features accompanying charger detection ICs make them an extremely attractive integrated circuit.

References
1. This specification is identified now as BC1.2; see http://www.usb.org/developers/docs/devclass_docs/ )
2. The phrase, "keeping up with the Joneses," is an American English idiom. For some background on the history and evolving meaning of the phrase, see the Wikipedia entry at http://en.wikipedia.org/wiki/Keeping_up_with_the_Joneses . Also The Phrase Finder at http://www.phrases.org.uk/meanings/216400.html.
3. See http://europa.eu/rapid/press-release_MEMO-09-301_en.htm.
4. See http://www.usb.org/press/USB-IF_Press_Releases/CENELEC_USB-IF.PDF. Also http://europa.eu/rapid/press-release_MEMO-09-301_en.htm.
5. See http://www.gsma.com/newsroom/mobile-industry-unites-to-drive-universal-charging-solution-for-mobile-phones/#.U1VOcPly7L8.
6. See China Communications Standards Association, "Technical Requirements and Test Method of Charger and Interface for Mobile Telecommunication Terminal Equipment" (CCSA YD/T 1591C2006, later updated to YD/T 1591C2009). Also Telecommunications Technology Association of South Korea, "Standard on I/O Connection Interface of Digital Cellular Phone" TTAS.KO-06.0028 released in March 2001. Later updated in 2002 (/R2), and in 2007 (/R4).
7. "Press Release: Universal phone charger standard approvedOne-size-fits-all solution will dramatically cut waste and GHG emissions". Itu.int. 22 October 2009. Retrieved 4 November 2009, at http://www.itu.int/newsroom/press_releases/2009/49.html.

About the author
Mohamed Ismail is with Maxim Integrated.


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