USB battery charging rev. 1.2: Important role of charger detectors: Page 5 of 8

November 06, 2014 //By Mohamed Ismail
USB battery charging rev. 1.2: Important role of charger detectors
Mohamed Ismail of Maxim Integrated considers the role of charger detectors in the USB battery charging specification rev. 1.2:
these proprietary chargers identify themselves to end devices by the voltage level set by a resistive-divider between VBUS and ground. Depending on the level of coverage required by a charger detecting circuit, sensing circuitry can be added to detect the voltage levels on D+ and D- and, thus, to identify different manufacturer-specific chargers.

Charger Detection Technology
A USB charger detection IC is a single chip that implements many of the features and intricacies associated with BC1.2 charger detection. It is, admittedly, possible to implement the detection scheme discretely. But the number of components, board space, and time spent getting the discrete system to operate successfully would increase dramatically.
Adding a dedicated charger detection chip requires some additional board space, so manufacturers often combine other necessary or desirable features into the same package. Consequently, charger detection ICs are highly integrated with a myriad of additional features such as built-in switches for USB or UART/audio operation, serial control interfaces, overvoltage protection (OVP), USB OTG support, Li+ battery charging capability, or even the ability to perform USB enumeration.
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.

Figure 3. MAX14636 charger

Design category: 

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