The universal serial bus (USB) provides a low cost solution for attaching peripheral devices to a host, such as a host computer or host server, so that the peripheral devices and the host can communicate with each other. Devices that are attached to a USB bus are automatically detected, and software automatically configures the devices for immediate use typically without user intervention. The USB devices/peripherals may include devices such as printers, scanners, keyboards, a mouse, digital cameras, digital video cameras, data acquisition devices, modems, speakers, telephones or video phones, storage devices such as ZIP drives, or other peripherals or devices. A USB bus can be extended with a hub which permits additions peripherals, or other hubs, to be coupled to a USB bus.
The USB specification entitled “Universal Serial Bus Revision 2.0 Specification” available at www.usb.org, the disclosure of which is hereby incorporated by reference in its entirety, dictates various requirements and protocols for devices connected with a USB bus. For example, issues relating to power management are included in the USB specification. In particular, the USB specifications define that devices may be low power devices drawing up to 100 mA of power from the USB connection or high power devices drawing up to 500 mA of power from the USB connection.
Recently, several extensions were added to the USB specification including an “on the go” (OTG) feature. The OTG feature permits two USB devices coupled to one another to communicate without the presence of a host computer. Another extension was added to delineate protocol for dedicated battery chargers, use of USB host as battery chargers, and a “No Dead Battery” provision to allow USB devices to temporarily draw power during connection to each other. Several different configurations have been produced to integrate the aforementioned USB protocol extensions. However, the configurations either introduce additional external hardware, which increases board area, or do not operate independently off of a battery or other external power supply.