Method and apparatus for operating a DC/DC converter

1. A method of operating a DC/DC converter in a continuous-conduction mode (CCM) or in a discontinuous-conduction mode (DCM) to produce an output voltage, the DC/DC converter setting a pulse width modulation in CCM based on a COMP signal that varies as a function of the output voltage, the method comprising:

capturing the COMP signal utilizing a digital-to-analog converter at a transition between CCM and DCM; and

varying a frequency of operation of the DC/DC converter in DCM based on the captured COMP signal, by comparing a difference between the captured COMP signal with the actual COMP signal during every cycle of the DC/DC converter.

2. The method of claim 1 , wherein varying the frequency of operation of the DC/DC converter in DCM based on the captured COMP signal comprises generating an error voltage based on the output voltage and a reference voltage, and varying the COMP signal in DCM based on the error voltage and the captured COMP signal.

3. The method of claim 1 , wherein capturing the COMP signal utilizing a digital-to-analog converter at a transition between CCM and DCM comprises generating a digital representation of the COMP signal, and converting the digital representation of the COMP signal to the captured COMP signal with the digital-to-analog converter.

4. The method of claim 3 , wherein generating a digital representation of the COMP signal comprises comparing the COMP signal to the captured COMP signal, and outputting a result of the comparison to an N-bit up/down counter, the N-bit up/down counter configured to generate the digital representation of the COMP signal from the result of the comparison.

5. The method of claim 3 , further comprising converging the captured COMP signal to the COMP signal during CCM operation of the DC/DC converter.

6. The method of claim 1 , wherein capturing the COMP signal utilizing a digital-to-analog converter at a transition between CCM and DCM comprises generating a digital representation of the COMP signal based on the output voltage Vout divided by a constant K.

7. A method of operating a DC/DC converter in a continuous-conduction mode (CCM) or in a discontinuous-conduction mode (DCM) to produce an output voltage, the DC/DC converter setting a pulse width modulation in CCM based on a COMP signal that varies as a function of the output voltage, the method comprising:

capturing the COMP signal utilizing a digital-to-analog converter at a transition between CCM and DCM; and

varying a frequency of operation of the DC/DC converter in DCM based on the captured COMP signal, wherein varying the frequency of operation of the DC/DC converter in DCM based on the captured COMP signal comprises generating an error voltage based on the output voltage and a reference voltage, and varying the COMP signal in DCM based on the error voltage and the captured COMP signal and wherein varying the frequency of operation of the DC/DC converter in DCM based on the captured COMP signal further comprises generating a rising ramp RAMPr signal and a falling ramp RAMPf signal based on the captured COMP signal, comparing the falling ramp RAMPf signal to the varied COMP signal to generate a START_ON_TIME signal, and varying the frequency of operation of the DC/DC converter based on the START_ON_TIME signal.

8. The method of claim 7 , wherein varying the frequency of operation of the DC/DC converter in DCM based on the captured COMP signal further comprises comparing the rising ramp RAMPr signal to a voltage signal derived from the captured COMP signal to generate an END_ON_TIME signal, generating a PWM_DCM control signal based on the START_ON_TIME signal and the END_ON_TIME signal, and varying the frequency of operation of the DC/DC converter based on the PWM_DCM control signal.

9. The method of claim 8 , further comprising comparing the rising ramp RAMPr signal to the COMP signal to generate a PWM_CCM control signal, and controlling operation of the DC/DC converter in CCM based on the PWM_CCM control signal.

10. A DC/DC converter that operates in a continuous-conduction mode (CCM) or in a discontinuous-conduction mode (DCM) to produce an output voltage, the DC/DC converter setting a pulse width modulation in CCM based on a COMP signal that varies as a function of the output voltage, comprising:

a digital-to-analog converter that captures the COMP signal at a transition between CCM and DCM; and

a driver configured to vary the frequency of operation of the DC/DC converter in DCM based on the captured COMP signal, by comparing a difference between the captured COMP signal with the actual COMP signal during every cycle of the DC/DC converter.

11. The DC/DC converter of claim 10 , further comprising an error amplifier configured to generate an error voltage based on the output voltage and a reference voltage.

12. The DC/DC converter of claim 10 , further comprising an N-bit up/down counter configured to generate a digital representation of the COMP signal captured at the transition from CCM to DCM, wherein the digital-to-analog converter converts the digital representation of the COMP signal to the captured COMP signal.

13. The DC/DC converter of claim 12 , further comprising a fourth comparator configured to compare the COMP signal to the captured COMP signal, and output a result of the comparison to the N-bit up/down counter, the N-bit up/down counter configured to generate the digital representation of the COMP signal from the result of the comparison.

14. The DC/DC converter of claim 13 , wherein the N-bit up/down counter and the digital-to-analog converter are configured to converge the captured COMP signal to the COMP signal during CCM operation of the DC/DC converter.

15. A DC/DC converter that operates in a continuous-conduction mode (CCM) or in a discontinuous-conduction mode (DCM) to produce an output voltage, the DC/DC converter setting a pulse width modulation in CCM based on a COMP signal that varies as a function of the output voltage, comprising:

a digital-to-analog converter that captures the COMP signal at a transition between CCM and DCM; and

a driver configured to vary the frequency of operation of the DC/DC converter in DCM based on the captured COMP signal

further comprising:

a voltage level generator configured to generate a falling RAMP lower limit voltage, a lower limit error voltage, and a CCM/DCM boundary COMP voltage;

an error amplifier configured to generate an error voltage based on the output voltage and a reference voltage; and

an error voltage controller configured to vary the COMP signal in DCM based on the error voltage and the lower limit error voltage.

16. The DC/DC converter of claim 15 , further comprising:

a ramp generator configured to generate a rising ramp RAMPr signal and a falling ramp RAMPf signal;

a first comparator configured to compare the falling ramp RAMPf signal to the varied COMP signal to generate a START_ON_TIME signal;

a second comparator configured to compare the rising ramp RAMPr signal to the CCM/DCM boundary COMP voltage to generate an END_ON_TIME signal; and

logic configured to receive the START_ON_TIME signal and the END_ON_TIME signal and to generate a PWM_DCM control signal.

17. The DC/DC converter of claim 16 , further comprising a third comparator configured to compare the rising ramp RAMPr signal to the COMP signal to generate a PWM_CCM control signal.

18. The DC/DC converter of claim 17 , further comprising a switch controller configured to vary the frequency of operation of the DC/DC converter in DCM based on the PWM_CCM control signal.

19. The DC/DC converter of claim 18 , wherein the switch controller is further configured to control operation of the DC/DC converter in CCM based on the PWM_CCM control signal.