MPS generation system and method

1. A powered device (PD) interface comprising:

a first terminal and a second terminal arranged for connection towards a power supply equipment;

a maintain power signature (MPS) circuitry;

a current sense circuitry arranged to sense the magnitude of a current flowing therethrough; and

a control circuitry in communication with said current sense circuitry, said MPS circuitry responsive to said control circuitry,

wherein said MPS circuitry is arranged, at a predetermined frequency, responsive to said control circuitry, to alternately:

output a first current pulse for a predetermined first time period; and

not output said first current pulse for a predetermined first off time period,

upon completion of said output second current pulse, not output either of said first current pulse or said second current pulse for a predetermined second off time period having a length that is generally equal to the length of said predetermined first off time period; and

upon completion of said second off time period, output said first current pulse;

wherein said control circuitry is arranged, responsive to said sensed current magnitude, to determine the magnitude of a current drawn by an input capacitor of a direct-current to direct-current (DC to DC) converter, and

wherein said control circuitry is arranged, responsive to said determined input capacitor current magnitude, to control said MPS circuitry to output a second current pulse for a predetermined second time period during said predetermined first off time period.

2. The PD interface of claim 1 , wherein said current sense circuitry is coupled between said MPS circuitry and one of said first terminal and said second terminal, and

wherein said input capacitor current magnitude determination comprises a comparison of said sensed current magnitude with the magnitude of said first current pulse.

3. The PD interface of claim 1 , wherein said current sense circuitry is coupled between said MPS circuitry and the DC to DC converter input capacitor.

4. The PD interface of claim 1 , wherein said predetermined second time period is greater than said predetermined first time period.

5. A maintain power signature (MPS) generation method, the method comprising:

at a predetermined frequency, alternately outputting between a first terminal and a second terminal a first MPS current pulse for a predetermined first time period and not outputting said first MPS current pulse for a predetermined first off time period;

during said first time period, determining the magnitude of a current drawn by an input capacitor of a direct-current to direct-current (DC to EXT) converter;

responsive to said determined input capacitor current magnitude, outputting between the first terminal and the second terminal a second MPS current pulse for a predetermined second time period during said predetermined first off time period;

upon completion of said output second current pulse, not outputting either of said first current pulse or said second current pulse for a predetermined second off time period having a length that is generally equal to the length of said predetermined first off time period; and

upon completion of said predetermined second off time period, outputting said first current pulse.

6. The method of claim 5 , wherein said input capacitor current magnitude determination comprises:

sensing the magnitude of a combination of said output first MPS current pulse and the input capacitor current; and

comparing said sensed combination current magnitude with the magnitude of said output first MPS current pulse, said second current pulse output only in the event that said sensed combination current magnitude is less than said current pulse magnitude for a predetermined evaluation time period.

7. The method of claim 5 , wherein said input capacitor current magnitude determination comprises sensing the magnitude of current being drawn by the input capacitor.

8. The method of claim 5 , wherein said predetermined second time period is greater than said predetermined first time period.

9. A powered device (PD) interface comprising:

a first terminal and a second terminal arranged for connection towards a power supply equipment;

a maintain power signature (MPS) circuitry;

a current sense circuitry arranged to sense the magnitude of a current flowing therethrough; and

a control circuitry in communication with said current sense circuitry, said MPS circuitry responsive to said control circuitry,

wherein said MPS circuitry is arranged, at a predetermined frequency, responsive to said control circuitry, to alternately:

output a first current pulse for a predetermined first time period; and

not output said first current pulse for a predetermined first off time period,

wherein said control circuitry is arranged, responsive to said sensed current magnitude, to determine the magnitude of a current drawn by an input capacitor of a direct-current to direct-current (DC to DC) converter, and

wherein said control circuitry is arranged, responsive to said determined input capacitor current magnitude, to control said MPS circuitry to output a second current pulse for predetermined second time period during said predetermined first off time period;

wherein said MPS circuitry is further arranged to:

upon completion of said output second current pulse, not output either of said first current pulse or said second current pulse for a predetermined second off time period having a length set such that said predetermined frequency is maintained; and

upon completion of said second off time period, output said first current pulse.

10. The PD interface of claim 9 , where in said current sense circuitry is coupled between said MPS circuitry and one of said first terminal and said second terminal, and

wherein said input capacitor current magnitude determination comprises a comparison of said current magnitude with the magnitude of said first current pulse.

11. The PD interface of claim 9 , wherein said current sense circuitry is coupled between said MPS circuitry and the DC to DC converter input capacitor.

12. The PD interface of claim 9 , wherein said predetermined second time period is greater than said predetermined first time period.

13. A maintain power signature (MPS) generation method, the method comprising:

at a predetermined frequency, alternately outputting between a first terminal and a second terminal a first MPS current pulse for a predetermined first time period and not outputting said first MPS current pulse for a predetermined first off time period;

during said first time period, determining the magnitude of a current drawn by an input capacitor of a direct-current to direct-current (DC to EXT) converter;

responsive to said determined input capacitor current magnitude, outputting between the first terminal and the second terminal a second MPS current pulse for a predetermined second time period during said predetermined first off time period;

upon completion of said output second current pulse, not outputting either of said first current pulse or said second current pulse for a predetermined second off time period having a length set such that said predetermined frequency is maintained; and

upon completion of said predetermined second off time period, outputting said first current pulse.

14. The method of claim 13 , wherein said input capacitor current magnitude determination comprises:

sensing the magnitude of a combination of said output first MPS current pulse and the input capacitor current; and

comparing said sensed combination current magnitude with the magnitude of said output first MPS current pulse, said second current pulse output only in the event that said sensed combination current magnitude is less than the magnitude of said output first MPS current pulse for a predetermined evaluation time period.

15. The method of claim 13 , wherein said input capacitor current magnitude determination comprises sensing the magnitude of current being drawn by the input capacitor.

16. The method of claim 13 , wherein said predetermined second time period is greater than said predetermined first time period.