Capacitor DC-DC converter with PFM and gain hopping

• US 6,055,168 A
• Filed: 05/28/1999
• Issued: 04/25/2000
• Est. Priority Date: 03/04/1998
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: McIntyre, William J., Kotowski, Jeff, Parry, John P.
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/322,322
• Time in Patent Office: 333 Days
• Field of Search: 363/59, 363/60, 307/109, 307/110, 323/209
• US Class Current: 363/60
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps

Abstract

A structure and method are provided for converting unregulated DC voltages to regulated DC voltages using pulse frequency modulation (PFM) and a switched capacitor array capable of multiple gains, where gain selection is based on the output voltage. The selected gain is maintained at or above a minimum gain determined from the input voltage. A regulated voltage, which is equal to or greater than a desired output voltage, is thus available to the load over a wider range of inputs and with greater conversion efficiency.

Claims

1. A DC-DC converter having an input to be connected to a power source and an output to be connected to a load, said converter comprising:

a switched capacitor array circuit including at least one capacitor and switching circuitry coupled to the capacitor, with the array circuit being switchable between a first gain state and a second gain state greater than the first gain state, with each gain state having first and second phases;

pump control circuitry coupled to the switching circuitry and configured to control switching of the capacitor array circuit between the first and second phases; and

gain change circuitry configured to control the gain state of the switched capacitor array circuitry, with the gain change circuitry operating to change the gain state of the switched capacitor array circuit from the first gain state to the second gain state based upon a number of times the switched capacitor array circuit has been switched between the first and second phases when in the first gain state.

2. The converter of claim 1 wherein the array circuit is further switchable between a third gain state and the second gain state, with the third gain state being greater than the second gain state and wherein the gain change circuitry further operates to change the gain state of the switched capacitor array circuit from the second gain state to the third gain state based upon a number of times the switched capacitor array circuit has been switched between the first and second phases when in the second gain state.

3. The converter of claim 1 further including compare circuitry configured to produce a compare signal switchable between a first signal state when an output voltage at the output of the converter has a magnitude less than a magnitude of a target voltage and a second signal state when the output voltage magnitude is greater than the magnitude of the target voltage and wherein the gain change circuitry changes the gain from the first to the second gain state based upon a duration of the compare signal in the first signal state.

4. The converter of claim 3 wherein the gain change circuitry further operates to change the gain state of the switched capacitor array circuit from the second gain state to the first gain state based upon a duration of the compare signal in the second signal state.

5. The converter of claim 4 wherein the pump control circuitry causes the switched capacitor array circuit to switch between the first and second phases K number of times when the compare signal is in the first signal state and wherein the gain change circuitry operates to change the switched capacitor array circuit from the first gain state to the second gain state when K reaches a predetermined value.

6. The converter of claim 5 wherein the pump control circuitry causes the switched capacitor array circuit to switch between the first and second phases every first time interval when the compare signal is in the first signal state and wherein the gain change circuitry operates to change the switched capacitor array circuit from the second gain state to the first gain state when the compare signal is in the second state for a duration equal to M number of the first time intervals.

7. The converter of claim 6 wherein the gain change circuitry includes a counter for determining a value of K.

8. The converter of claim 7 wherein the gain change circuitry includes a counter for determining a value of M.

9. The converter of claim 8 wherein the gain change circuitry includes an up/down counter for determining the values of K and M.

10. The converter of claim 9 wherein the gain change circuitry is further configured to prevent the switched capacitor array circuit from switching from the second gain state to the first gain state in response to converter operating conditions and independent of the compare signal.

11. The converter of claim 10 wherein the converter operation conditions includes the magnitude of the input voltage.

12. A DC-DC converter having an input to be connected to a power source and a regulated output, said converter comprising:

compare circuitry configured to produce a compare signal indicative of a relative magnitude of an output voltage of the converter and a target voltage;

a switched capacitor array circuit including at least one capacitor and switching circuitry coupled to the capacitor, with the array circuit being switchable between a first gain state and a second gain state greater than the first gain state, with each gain state having first and second phases;

pump control circuitry coupled to the switching circuitry and configured to control, in response to the compare signal, switching of the capacitor array circuit between the first and second phases; and

gain change circuitry configured to control the gain state of the switched capacitor array circuitry and to change the switched capacitor array circuit from the first to the second gain state in response to the compare signal and to change the switched capacitor array circuit from the second to the first gain state in response to the compare signal.

13. The converter of claim 12 wherein the pump control circuitry causes the switched capacitor array circuit to switch between the first and second phases when the compare signal is in a first signal state indicating that the output voltage magnitude is less than the target voltage magnitude and prevents the switched capacitor array circuit from switching between the first and second phases when the compare signal is in a second signal state indicating that the output voltage magnitude is greater than the target voltage magnitude.

14. The converter of claim 13 wherein the pump control circuitry causes the switched capacitor array circuit to switch between the first and second phases K number of times when the compare signal is in the first signal state and wherein the gain change circuitry operates to change the switched capacitor array circuit from the first gain state to the second gain state when K reaches a predetermined value.

15. The converter of claim 14 wherein the pump control circuitry causes the switched capacitor array circuit to switch between the first and second phases every first time interval when the compare signal is in the first state and wherein the gain change circuitry operates to change the switched capacitor array circuit from the second gain state to the first gain state when the compare signal is in the second state for a duration equal to M number of the first time intervals.

16. The converter of claim 15 wherein the gain change circuitry includes a counter for determining a value of K.

17. The converter of claim 16 wherein the gain change circuitry includes a counter for determining a value of M.

18. The converter of claim 17 wherein the gain change circuitry includes an up/down counter for determining the values of K and M.

19. The converter of claim 18 wherein the gain change circuitry is further configured to prevent the switched capacitor array circuit from switching from the second gain state to the first gain state in response to converter operating conditions and independent of the compare signal.

20. The converter of claim 19 wherein the converter operating conditions include the magnitude of the input voltage.

21. A DC-DC converter having an input to be connected to a power source and an output to be connected to a load, said converter comprising:

a switched capacitor array circuit including at least two capacitors and switching circuitry coupled to the capacitors, with the array circuit being switchable to first, second and third gain states of differing gain magnitudes and with the array circuit being switchable between phases in each of the gain states so that the array circuit receives charge from the power source and so that the array transfers charge to the load;

pump control circuitry coupled to the switching circuitry and configured to control switching of the capacitor array circuit between the phases;

compare circuitry configured to produce a compare signal indicative of a relative magnitude of an output voltage of the converter and a single target voltage; and

gain change circuitry configured to switch the switched capacitor array from any one of the first, second and third gain states to another one of the first, second and third gains states based upon the compare signal.

22. The converter of claim 21 wherein the compare signal is in a first signal state when the output voltage magnitude is less than the target voltage magnitude and a second signal state when the output voltage magnitude is greater than the target voltage magnitude and wherein the gain change circuitry operates to increase the gain magnitude when the compare signal is in the first signal state.

23. The converter of claim 22 wherein the gain change circuitry operates to increase the gain magnitude when the compare signal is in the first signal state longer than a first predetermined time period.

24. The converter of claim 23 wherein the gain change circuitry operates to decrease the gain magnitude when the compare signal is in the second signal state longer than a second predetermined time period.

25. The converter of claim 22 wherein the pump control circuitry causes the switched capacitor array circuit to switch between the phases once every unit time period when the compare signal is in the first gain state and wherein the gain change circuitry operates to increase the gain magnitude when the compare signal is in the first signal state for a duration of more than K number of the time periods.

26. The converter of claim 25 wherein the gain change circuitry operates to decrease the gain magnitude when the compare signal is in the second signal state for a duration of more than M number of the time periods.

27. The converter of claim 26 wherein K is greater than M.

28. The converter of claim 21 wherein the gain change circuitry further includes minimum gain circuitry configured to prevent the switched capacitor array circuit from switching from the second gain state to the first gain state based upon one of the input voltage magnitude and the output voltage magnitude.

29. The converter of claim 28 wherein the minimum gain circuitry operation is based upon both of the input and output voltage magnitudes.

30. The converter of claim 29 wherein the minimum gain circuitry operation is based upon a ratio of the input and output voltage magnitudes.

34. The converter of claim 30 wherein the switched capacitor array circuit switches between phases one every time period and wherein the gain change circuitry operates to increase the gain state when the compare signal is in the first signal state for a duration of more than K number of the time periods.

35. The converter of claim 34 wherein the gain change circuitry operates to decrease the gain state when the compare signal is in the second state for a duration of more than M number of the time periods.

31. A DC-DC converter having an input to be connected to a power source and an output to be connected to a load, said converter comprising:

a switched capacitor array circuit including at least two capacitors and switching circuitry coupled to the capacitors, with the array circuit being switchable to first, second and third gain states, with the first gain state providing a gain less than one, the third gain state providing a gain of greater than one and the second gain state providing a gain intermediate the first and second gain states and with the array circuit being switchable between phases in each of the gain states so that the array circuit receives charge from the power source and so that the array transfers charge to the load;

pump control circuitry coupled to the switching circuitry and configured to control switching of the switched capacitor array circuit between the phases;

compare circuitry configured to produce a compare signal indicative of a magnitude of an output voltage of the converter relative to a single target voltage; and

gain change circuitry operable to switch the switched capacitor array circuit between any of the first, second and third gain states in response to the compare signal.

32. The converter of claim 31 wherein the pump control circuitry causes the switched capacitor array circuit to switch between the phases when the compare signal is in a first signal state and where the pump control circuitry ceases to switch between the phases when the compare signal is in a second signal state different from the first signal state.

33. The converter of claim 32 wherein the gain change circuitry operates to increase the gain state of the switched capacitor array circuit when the compare signal is in the second signal state for more than a first predetermined time period and to decease the gain state when the compare signal is in the first signal state for more than a second predetermined time period.

36. A DC-DC converter having an input to be connected to a power source and an output to be connected to a load, said converter comprising:

a switched capacitor array circuit including at least one capacitor and switching circuitry coupled to the capacitor, with the array circuit being switchable between a first gain state and a second gain state greater than the first gain state, with each gain state having first and second phases, with the first and second phases comprising one pump cycle;

pump control circuitry coupled to the switching circuitry and configured to control switching of the capacitor array circuit; and

gain change circuitry configured to switch the switched capacitor array circuit from the first gain state to the second gain state when the switched capacitor array circuit has been switched more that a predetermined number of consecutive pump cycles when in the first gain state.

37. The converter of claim 36 wherein each of the consecutive pump cycles has a first time period and wherein the gain change circuitry is further configured to switch from the second gain state to the first gain state when the switched capacitor array circuit has not been switched for more than a predetermined number of the first time periods.

38. The converter of claim 36 further comprising compare circuitry configured to produce a compare signal having a first signal state when a magnitude of an output voltage of the converter is less than a magnitude of a target voltage and having a second signal state when the magnitude of the output voltage is greater than the magnitude of the target voltage and wherein the switched capacitor array circuit is switched between phases only when the compare signal is in the first signal state.

39. A DC-DC converter having an input to be connected to a power source and an output to be connected to a load, said converter comprising:

a switched capacitor array circuit including at least one capacitor and switching circuitry coupled to the capacitor, with the array circuit being switchable between a first gain state and a second gain state greater than the first gain state, with each gain state having first and second phases, with the first and second phases comprising one pump cycle;

pump control circuitry coupled to the switching circuitry and configured to control switching of the capacitor array circuit between the first and second phases;

compare circuitry configured to produce a compare signal of a first signal state when an output voltage magnitude is less than a target voltage magnitude and of a second signal state when the output voltage magnitude is greater than the target voltage magnitude; and

gain change circuitry configured to switch the switched capacitor array circuit from the first gain state to the second gain state when a ratio of a duration of the compare signal in the first signal state to a duration of the compare signal is the second signal state is greater than a first predetermined value.

40. The converter circuit of claim 39 wherein the gain change circuitry is configured to switch the switched capacitor array circuit from the second gain state to the first gain state when the ratio is less than a second predetermined value.

41. The converter of claim 40 wherein the switched capacitor array circuit switches between the first and second phases once every first time interval and wherein the gain change circuitry causes the switched capacitor array circuit to switch from the first gain state to the second gain state when the compare signal is in the first signal state for a duration greater than K number of the first time intervals.

42. The converter of claim 41 wherein the gain change circuitry causes the switched capacitor array circuit to switch from the second gain state to the first gain state when the compare signal is in the second signal state for a duration greater than M number of the first time periods.

43. A method of controlling a switched capacitor array circuit of a DC-DC converter, with the switched capacitor array circuit including at least two capacitors and switching circuitry coupled to the capacitors, with the array circuit being switchable to first, second and third gain states, with the first gain state providing a gain less than one, the third gain state providing a gain of greater than one and the second gain state providing a gain intermediate the first and second gain states and with the array circuit being switchable between phases in each of the gain states so that the array circuit receives charge from the power source and so that the array transfers charge to the load, said method comprising:

coupling a power source to an input of the switched capacitor array circuit;

coupling a load to an output of the switched capacitor array circuit;

producing a compare signal indicative of a magnitude of an output voltage of converter;

switching the switched capacitor array circuit between phases when the compare signal is in a first signal state;

not switching the switched capacitor array circuit between phases when the compare signal is in a second signal state, different than the first signal state; and

increasing the gain state of the switched capacitor array circuit when the compare signal is in the first signal state for longer than a first predetermined time period.

44. The method of claim 43 further including decreasing the gain state when the compare signal is in the second signal state for longer than a second predetermined time period.

45. The method of claim 44 further including preventing the gain state from being decreased below a minimum gain value, with the minimum gain value being determined by one of the input voltage of the switched capacitor array circuit and the output voltage of the switched capacitor array circuit.

46. The method of claim 45 wherein the preventing is determined by both the input and the output voltages.

47. A method of controlling a switched capacitor array circuit of a DC-DC converter, with the switched capacitor array circuit including at least one capacitor and switching circuitry coupled to the capacitor, with the array circuit being switchable between a first gain state and a second gain state greater than the first gain state, with each gain state having first and second phases, said method comprising:

coupling a power source to an input of the switched capacitor array circuit;

coupling a load to an output of the switched capacitor array circuit;

producing a compare signal indicative of a magnitude of an output voltage of converter;

switching the switched capacitor array circuit between the first and second phases when the compare signal is in a first signal state;

not switching the switched capacitor array circuit between the first and second phases when the compare signal is in a second signal state, different than the first signal state; and

increasing the gain state of the switched capacitor array circuit when the switched capacitor array circuit has been switched for K number of times prior to the compare signal changing from the first signal state to the second signal state.

48. The method of claim 47 further including decreasing the gain state of the switched capacitor array circuit when the compare signal has been in the second signal state for more that a predetermined time period.

49. The method of claim 48 where the switched capacitor array circuit is switched between the first and second phases once every first time period and wherein the decreasing occurs when M number of the first time periods have elapsed prior to the compare signal changing from the second signal state to the first signal state.