The following overview references v

The following overview references various industry standards. It is always recommended to consult the most up-to-date standard to ensure the most recent and accurate information. Rechargeable portable equipment requires an external power source to charge its batteries. USB ports are a convenient location for charging because of an available 5V power source. Universally accepted standards are required to make sure 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 500mA to downstream client-side devices. Because multiple USB devices can be attached to a single USB port through a buspowered hub, it is the responsibility of the client-side device to negotiate its power allotment from the host to ensure the total current draw does not exceed 500mA. In general, each USB device is granted 100mA and may request more current in 100mA unit steps up to 500mA. The host may grant or deny based on the available current. A USB 3.0 host port not only provides higher data rate than USB 2.0 port but also raises the unit load from 100mA to 150mA. It is also required to provide a minimum current of 900mA to downstream client-side devices.Additionally, the success of USB has made the mini-USB connector a popular choice for wall adapter cables. This 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 500mA minimum defined by USB 2.0 or 900mA for USB 3.0 has become insufficient for many handset and personal media players which need a higher charging rate. Wall adapters can provide much more current than 500mA/900mA. Several new standards have been introduced defining protocol handshaking methods that allow host and client devices to acknowledge and draw additional current beyond the 500mA/900mA minimum defined by USB 2.0/3.0 while still using a single micro-USB input connector. The PI5USB2546 supports four of the most common USB charging schemes found in popular hand-held media and cellular devices: