Patent ID: 7383452

Claim:
An electronic device capable of deriving power from a host computing device when connected to said host computing device through a Universal Serial Bus (USB) connection, said electronic device comprising: a processor; a power supply connection for connecting the electronic device to a power supply comprising any of an insertable battery pack, an alternating current (AC) power supply and an auxiliary power supply comprising a host computing device; a power management unit (PMU) coupled to the power supply connection and the processor for managing power allocated to the processor from the power supply; and a timing unit connected to the PMU and the power supply connection for sending electrical signals to the PMU for initiating power-up of the processor, the timing unit being adapted to send the electrical signals to input terminals of the PMU in response to any of the insertable battery pack, the AC power supply and the auxiliary power supply being connected to the electronic device; wherein the timing unit is further adapted to send the electrical signals after a time t 1 from a time when any of the insertable battery pack, the AC power supply and the auxiliary power supply is connected to the electronic device, the time t 1 being selected to be compatible with an operating specification of the PMU as a time required for the PMU to register a voltage transition at the input terminals of the PMU but within a power-up time starting from the time when any of the insertable battery pack, the AC power supply and the auxiliary power supply is connected to the electronic device, where the power-up time is less than a 100 ms time period allowed for the processor to power-up during an enumeration period defined by the USB standard for the electronic device to identify itself to the host computing device and negotiate power distribution from the host computing device.