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Power equals voltage times current. A USB port that draws 500 mA (0.5 A) at 5 volts is drawing 2.5 watts of power. In Bus-powered USB hubs, each USB port can supply power as well as transfer data. A self-powered hub takes its power from an external power supply unit and can therefore provide full power (up to 500 mA) to every port. Self-powered ...
A number of extensions to the USB Specifications have progressively further increased the maximum allowable V_BUS voltage: starting with 6.0 V with USB BC 1.2, [43] to 21.5 V with USB PD 2.0 [44] and 50.9 V with USB PD 3.1, [44] while still maintaining backwards compatibility with USB 2.0 by requiring various forms of handshake before ...
All devices must act as low-power devices when starting out as unconfigured. For USB devices up to USB 2.0 a unit load is 100 mA (or 500 mW), while USB 3.0 defines a unit load as 150 mA (750 mW). Full-featured USB-C can support low-power devices with a unit load of 250 mA (or 1250 mW).
V BUS and GND provide 5 V up to 500 mA of current. However, to connect a USB 2.0/1.1 device to a USB-C host, use of pull-down resistors Rd [63] on the CC pins is required, as the source (host) will not supply V BUS until a connection is detected through the CC pins.
As with earlier versions of USB, USB 3.0 provides power at 5 volts nominal. The available current for low-power (one unit load) SuperSpeed devices is 150 mA, an increase from the 100 mA defined in USB 2.0. For high-power SuperSpeed devices, the limit is six unit loads or 900 mA (4.5 W)—almost twice USB 2.0's 500 mA.
The written USB 3.0 specification was released by Intel and its partners in August 2008. The first USB 3.0 controller chips were sampled by NEC in May 2009, [4] and the first products using the USB 3.0 specification arrived in January 2010. [5] USB 3.0 connectors are generally backward compatible, but include new wiring and full-duplex operation.