Apparatus and method to support USB enumeration of a bus powered handheld device

摘要

The proposed solution relates to enumeration of a handheld device by a host controller in a laptop, and more particularly to a method and apparatus to support USB enumeration of such a handheld device where greater than 100 mA is required to enumerate the chipset associated with the handheld device. The proposed solution comprises a handheld device with an added USB microcontroller. In operation, the integrated USB microcontroller is only powered up when the USB charging cable is plugged in and the rechargeable battery level is below the threshold required to power up the handheld device with less than 100 mA pre-enumeration USB current. The integrated USB microcontroller performs USB enumeration with the host controller using the pre-enumeration 100 mA current, so that the charging current can be increased to 500 mA post enumeration. Once the rechargeable battery is charged to above the threshold for the handheld device's chipset or when 500 mA current can be drawn from it, the chipset of the handheld device is powered up to take over USB communication from the USB microcontroller.