The following overview references various industry standards. TI recommends consulting the most up-to-date standards to ensure the most recent and accurate information. Rechargeable portable equipment requires an external power source to charge batteries. USB ports are a convenient location for charging because of an available 5-V power source. Universally accepted standards are required to ensure host and client-side devices operate together in a system to ensure power-management requirements are met. Traditionally, host ports following the USB-2.0 specification must provide at least 500 mA to downstream client-side devices. Because multiple USB devices can be attached to a single USB port through a bus-powered hub, the client-side device sets the power allotment from the host to ensure the total current draw does not exceed 500 mA. In general, each USB device is granted 100 mA and can request more current in 100-mA unit steps up to 500 mA. The host grants or denies additional current based on the available current. A USB-3.0 host port not only provides higher data rate than a USB-2.0 port but also raises the unit load from 100 mA to 150 mA. Providing a minimum current of 900 mA to downstream client-side devices is required.

Additionally, the success of USB has made the micro-USB and mini-USB connectors a popular choice for wall-adapter cables. A micro-USB or mini-USB allows a portable device to charge from both a wall adapter and USB port with only one connector. As USB charging has gained popularity, the 500-mA minimum defined by USB 2.0, or 900 mA for USB 3.0, has become insufficient for many handset and personal media players, which require a higher charging rate. Wall adapters provide much more current than 500 or 900 mA. Several new standards have been introduced defining protocol handshaking methods that allow host and client devices to acknowledge and draw additional current beyond the 500-mA and 900-mA minimum defined by USB 2.0 and USB 3.0, respectively, while still using a single micro-USB or mini-USB input connector.

The TPS2549-Q1 device supports four of the most-common USB-charging schemes found in popular hand-held media and cellular devices.

• USB Battery Charging Specification BC1.2
• Chinese Telecommunications Industry Standard YD/T 1591-2009
• Divider 3 mode
• 1.2-V mode

The BC1.2 specification includes three different port types:

• Standard downstream port (SDP)
• Charging downstream port (CDP)
• Dedicated charging port (DCP)

BC1.2 defines a charging port as a downstream-facing USB port that provides power for charging portable equipment. Under this definition, CDP and DCP are defined as charging ports.

Table 8-3 lists the difference between these port types.