Mechanism for charging portable device with USB dock

1. A Universal Serial Bus (USB) dock, comprising:

a plurality of downstream ports; and

a upstream port, for connecting the USB dock to a portable device, wherein the upstream port comprises an On-the-go (OTG) ID pin and a differential pair; and

a microcontroller, configured to detect operating states of the portable device,

wherein when it is detected that the portable device is in a USB OTG host mode and has entered a suspend state, the microcontroller controls the portable device to switch from the USB OTG host mode to a USB device mode by toggling a state of the USB OTG ID pin, thereby charging the portable device via the upstream port.

2. The USB dock as claimed in claim 1 , wherein the upstream port is implemented by the USB micro A/B interface.

3. The USB dock as claimed in claim 1 , wherein the upstream port is compatible with the USB micro A/B interface.

4. The USB dock as claimed in claim 1 , further comprising: a first button for toggling the portable device to switch from the USB device mode to the USB OTG host mode.

5. The USB dock as claimed in claim 1 , further comprising: a second button for controlling the portable device to enter the suspend state when the portable device is in the OTG host mode.

6. The USB dock as claimed in claim 1 , wherein when the portable device is in the USB OTG host mode, the microcontroller performs data transmission between the portable device and USB accessories connected to the downstream ports of the USB dock.

7. The USB dock as claimed in claim 1 , wherein the portable device issues a suspend command to the microcontroller when the portable device has entered the suspend state, and the microcontroller disconnects the differential pair and then re-activates the differential pair when the microcontroller has received the suspend command, such that the portable device enters the USB device mode from the USB OTG host mode.

8. The USB dock as claimed in claim 1 , wherein the microcontroller further shorts the differential pair to enable a rapid-charging mode when the portable device has entered the USB device mode.

9. The USB dock as claimed in claim 6 , wherein when a user sends a trigger signal by utilizing one of the USB accessories connected to the USB dock, the USB dock controls the portable device to enter the USB OTG host mode from the USB device mode in response to the trigger signal.

10. A method for charging a portable device with a USB dock, wherein the USB dock comprises a plurality of downstream ports and an upstream port, the method comprising:

connecting the USB dock to the portable device via the upstream port, wherein the upstream port comprises an On-the-go (OTG) ID pin and a differential pair;

detecting operating states of the portable device; and

controlling the portable device to switch from the USB OTG host mode to a USB device mode by toggling a state of the USB OTG ID pin to charge the portable device via the upstream port when it is detected that the portable device is in the USB OTG host mode and has entered a suspend state.

11. The method as claimed in claim 10 , wherein the upstream port is implemented by the USB micro A/B interface.

12. The method as claimed in claim 10 , wherein the upstream port is compatible with the USB micro A/B interface.

13. The method as claimed in claim 10 , wherein the USB dock further comprises a first button, and the method further comprises:

toggling the portable device to switch from the USB device mode to the USB OTG host mode by pushing the first button.

14. The method as claimed in claim 10 , wherein the USB dock further comprises a second button, and the method further comprises:

controlling the portable device to enter the suspend state when the portable device is in the OTG host mode by pushing the second button.

15. The method as claimed in claim 10 , further comprising:

performing data transmission between the portable device and USB accessories connected to the downstream ports of the USB dock when the portable device is in the USB OTG host mode.

16. The method as claimed in claim 10 , further comprising:

issuing a suspend command to a microcontroller by the portable device when the portable device has entered the suspend state; and

disconnecting the differential pair and then re-activating the differential pair by the microcontroller when the microcontroller has received the suspend command, such that the portable device enters the USB device mode from the USB OTG host mode.

17. The method as claimed in claim 10 , further comprising: shorting the differential pair to enable a rapid-charging mode when the portable device has entered the USB device mode.

18. The method as claimed in claim 15 , further comprising:

when a user sends a trigger signal by utilizing one of the USB accessories connected to the USB dock, controlling the USB dock to control the portable device to enter the USB OTG host mode from the USB device mode in response to the trigger signal.