Electronic device charging via an audio jack

1. A system comprising:

an electronic device comprising power management circuitry and comprising a universal serial bus (USB) connector having a first contact and a second contact, wherein:

in a first mode of operation, said power management circuitry is configured to output one or more audio signals via one or both of said first contact and said second contact; and

in a second mode of operation, said power management circuitry is configured to output a signal for delivering supply current via one or both of said first contact and said second contact;

said electronic device comprises circuitry operable to:

sense whether a second electronic device connected to said first contact and said second contact is capable of receiving a supply current via said first contact and said second contact; and

determine whether to transition between said first and second modes of operation based on an amount of current output by said power management circuitry.

2. The system of claim 1 , wherein:

while said electronic device is in said first mode of operation, a gain and/or volume limit of audio processing circuitry in said electronic device is set to a first level; and

while said electronic device is in said second mode of operation, said gain and/or volume limit of said audio processing circuitry is set to a second level that is higher than said first level.

3. The system of claim 2 , wherein said first level is determined compatible with speakers in said second device and said second level is determined incompatible with said speakers.

4. The system of claim 1 , wherein said signal for outputting said supply current is a sine wave having a frequency higher than 20 kHz.

5. The system of claim 1 , wherein said electronic device is operable to indicate to said second electronic device a desired mode of operation.

6. The system of claim 1 , wherein said second electronic device has a battery, wherein the electronic device is configured to:

when said electronic device is operating in said second mode, charge said battery using said supply current output via said one or both of said first contact and said second contact; and

when said electronic device is operating in said first mode, output said audio signals via said one or both of said first contact and said second contact.

7. A method comprising:

performing by circuitry of an electronic device that comprises a universal serial bus (USB) connector having a first contact and a second contact:

while said circuitry is in a first mode of operation, outputting one or more audio signals carrying via one or both of said first contact and said second contact; and

while said circuitry in a second mode of operation, outputting a signal for delivering supply current via one or both of said first contact and said second contact;

sensing whether a second electronic device coupled to said first contact and said second contact is capable of receiving a signal delivering a supply current; and

determining whether to transition between said first and second modes of operation based on an amount of current output by said circuitry.

8. The method of claim 7 , wherein:

while said circuitry is in said first mode of operation, setting a gain and/or volume limit of said circuitry to a first level; and

while said circuitry is in said second mode of operation, setting said gain and/or volume limit of said circuitry to a second level that is higher than said first level.

9. The method of claim 8 , wherein said first level is determined compatible with speakers in said second electronic device and said second level is determined incompatible with said speakers.

10. The method of claim 7 , wherein said signal for delivering said supply current is a sine wave having a frequency higher than 20 kHz.

11. The method of claim 7 , wherein said electronic device is operable to indicate to said second electronic device a desired mode of operation.

12. A system comprising:

an electronic device comprising power management circuitry and comprising a universal serial bus (USB) connector having a first contact and a second contact, wherein:

in a first mode of operation, said power management circuitry is configured to output one or more audio signals carrying music and/or voice via said one or both of said first contact and said second contact; and

in a second mode of operation, said power management circuitry is configured to output a signal for delivering supply current via said one or both of said first contact and said second contact;

said power management circuitry is operable to:

sense whether a second electronic device connected to said first contact and said second contact is capable of receiving said supply current via said first contact and said second contact; and

determine whether to transition between said first and second modes of operation based on an amount of current output by said power management circuitry.

13. The system of claim 12 , wherein:

while said electronic device is in said first mode of operation, a gain and/or volume limit of audio processing circuitry in said electronic device is set to a first level; and

while said electronic device is in said second mode of operation, said gain and/or volume limit of said audio processing circuitry is set to a second level that is higher than said first level.