Method and apparatus for handling a charging state in a mobile electronic device

1. A method for charging a mobile electronic device from a Universal Serial Bus (USB) host upon coupling the mobile electronic device to the USB host, comprising:

detecting that the mobile electronic device is in a device suspend state upon coupling of a USB interface of the device to the USB host;

sensing an input voltage from the USB host;

entering a device charging state in response to sensing the input voltage;

powering a processing device in the mobile electronic device from the input voltage while the mobile electronic device is in the device charging state;

enabling the processing device to receive and process control signals from the USB host;

requesting enumeration from the USB host; and

if an enumeration acknowledgement is not received from the USB host within a predetermined time period, then entering the device suspend state.

2. The method of claim 1 , wherein the predetermined time period is at least 100 ms.

3. The method of claim 1 , further comprising:

transmitting a time dependent enable signal to a battery charger circuitry in response to sensing the input voltage, the time dependent enable signal causing the mobile electronic device to enter the device charging state.

4. The method of claim 3 , further comprising:

receiving a device suspend state control signal from the USB host; and

in response to the device suspend state control signal, disabling the battery charger circuitry to enter the device suspend state.

5. A mobile electronic device, comprising:

a rechargeable power source;

a processing device configured to control the operation of the mobile electronic device;

a Universal Serial Bus (USB) interface for coupling the rechargeable power source and the processing device to a USB host;

the processing device being coupled to the rechargeable power source and the USB interface, wherein the processing device receive power from the rechargeable power source and from the USB host via the USB interface;

the USB interface being configured to detect that the mobile electronic device is in a device suspend state upon coupling of the USB interface to the USB host, and in response to detecting that the mobile electronic device is in the device suspend state when coupled to the USB host, power the processing device from the USB host for a predetermined time period while an enumeration request is transmitted to the USB host; and

the USB interface being further configured to disable power to the processing device from the USB host if an enumeration acknowledgement is not received from the USB host within the predetermined time period.

6. The mobile electronic device of claim 5 , wherein the USB interface comprises:

a battery charger circuitry that receives a power input from the USB host and generates a power output to the rechargeable power source and the processing device; and

a voltage supervisor and reset module configured to enable and disable the power output from the battery charger circuitry.

7. The mobile electronic device of claim 6 , wherein the voltage supervisor and reset module is further configured to receive a device suspend state control signal from the USB host causing the voltage supervisor and reset module to disable the battery charger.

8. The mobile electronic device of claim 6 , wherein the voltage supervisor and reset module is configured to detect the power input from the USB host.

9. The mobile electronic device of claim 8 , wherein the voltage supervisor and reset module is configured to activate a timer in response to detecting the power input from the USB host, wherein the timer is configured to determine when the predetermined time period has elapsed.

10. The mobile electronic device of claim 9 , wherein the voltage supervisor and reset module is configured to disable the battery charger is the timer expires before the voltage supervisor and reset module receives a signal from the processing device indicating that an enumeration acknowledgement has been received from the USB host.

11. The mobile electronic device of claim 5 , wherein the predetermined time period is at least 100 ms.