MC34825,pdf datasheet (Micro-U

The MC34825 is designed to support the Universal Charging Solution (UCS) recommended by the OMTP (Open Mobile Terminal Platform), as well as to use the same 5-pin micro or mini-USB connector for other wired accessories. The 34825 supports various types of external power supplies, such as a dedicated ac/dc adapter or a USB port, to charge the battery. It has functions built in to identify the type of the power supply, and sets low or high charging current, based on the current capability of the power supply. The 34825 monitors the power supply, and offers an up to 28 V of over-voltage protection (OVP) to the cell phone against failed power supplies. The 34825 also contains analog switches to multiplex the 5 pins, to support UART and high speed USB data communication, mono or stereo audio headset with or without a microphone and a cord remote controller, manufacturing or research-and-development (R/D) test cables, and other accessories.
The 34825 monitors both the VBUS status and the resistance between the ID pin and the ground to identify the accessory being plugged into the mini or micro-USB connector. A high-accuracy 5-bit ADC is offered to distinguish 32 levels of ID resistance that are assigned to buttons in a cord remote controller or to identification (ID) resistors of accessories. After identifying the attached accessory, the 34825 sends an interrupt signal to a host IC and the host IC can configure the analog switches via an I2C serial bus for further actions. When the accessory is detached from the cell phone, an interrupt signal is also sent to inform the host.