Bounded power supply voltage positioning

• US 6,472,856 B2
• Filed: 03/09/2001
• Issued: 10/29/2002
• Est. Priority Date: 03/09/2001
• Status: Expired due to Fees

• Current Assignee: Semtech Corporation
• Original Assignee: Semtech Corporation
• Inventors: Groom, Terry J., Pullen, Stuart
• Primary Examiner(s): Han, Jessica
• Application Number:
  US09/803,689
• Publication Number:
  US 20020125871A1
• Time in Patent Office: 599 Days
• Field of Search: 323/222, 323/282, 323/284, 323/285, 323/908
• US Class Current: 323/284
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load

Abstract

A voltage positioning technique allows a power supply controller to more fully exploit active voltage positioning as a way of maintaining supply voltage within the limits defined for an associated electrical load. The supply voltage is allowed to “droop” as a function of load current. Droop may be implemented in linear proportion to load current, or as a discrete droop function once load current exceeds a given threshold. In either case, the droop circuitry of the supply controller implements a bounding function that establishes an accurately known maximum droop voltage magnitude. This maximum droop voltage limit establishes a reliable lower limit for the supply voltage independent of increasing load current. This accurately set lower bound for the droop voltage enables the controller to more aggressively position the supply voltage at the lower voltage limit of the load, which minimizes voltage overshoot and load power consumption.

Claims

1. A bounded droop voltage circuit for use with a power supply providing a regulated output voltage signal to a load, said droop voltage circuit comprising:

a first circuit to generate a droop current signal proportional to a load current drawn from said regulated output voltage signal; and

a second circuit to generate a droop voltage signal based on said droop current signal to cause the power supply to reduce said regulated output voltage signal by an amount corresponding to said droop voltage signal, said second circuit including a limiting circuit to bound said droop voltage signal to a maximum value independent of the load current.

2. The bounded droop voltage circuit of claim 1 wherein said second circuit comprises a resistive circuit coupled at a first end to said first circuit to receive said droop current signal and coupled at a second end to said regulated output voltage signal, such that a regulation feedback voltage signal at said first end of said resistive circuit is the sum of said droop voltage signal which is developed across said resistive circuit and said regulated output signal.

3. The bounded droop voltage circuit of claim 2 wherein said limiting circuit comprises a current limiting circuit to fix a maximum value for said droop current signal based on a bounding voltage signal provided to said current limiting circuit.

4. The bounded droop voltage circuit of claim 2 wherein said limiting circuit comprises a voltage clamping circuit to fix a maximum value for said droop voltage signal developed across said resistive circuit.

5. The bounded droop voltage circuit of claim 4 wherein said voltage clamping circuit comprises a clamping diode coupled in parallel with said resistive circuit.

6. The bounded droop voltage circuit of claim 1 wherein said first circuit comprises a current source to generate said droop current signal in proportion to the load current.

7. The bounded droop voltage circuit of claim 6 wherein said current source comprises:

a transconductance amplifier to generate a reference current signal proportional to a differential input voltage signal that is dependent upon the load current; and

an operational amplifier circuit to generate said droop current signal proportional to said reference current signal.

8. The bounded droop voltage circuit of claim 7 wherein said current source further comprises gain setting resistors to set a current gain for said droop current signal relative to said reference current signal.

9. The bounded droop voltage circuit of claim 8 wherein at least one of said gain setting resistors comprises a user-selectable resistor element to permit setting said current gain as desired.

10. The bounded droop voltage circuit of claim 7 wherein said operational amplifier circuit comprises:

an operational amplifier with a first input terminal coupled to a first voltage signal determined by said reference current signal and a second input terminal coupled to a second voltage signal determined by said droop current signal; and

a pass transistor in a feedback loop of said operational amplifier to control said droop current signal responsive to an output signal of said operational amplifier such that a difference between said first and second voltage signals is minimized.

11. The bounded droop voltage circuit of claim 10 wherein said limiting circuit comprises a bounding circuit to override control of said pass transistor by said operational amplifier when said second voltage signal reaches the value of a bounding voltage signal.

12. The bounded droop voltage circuit of claim 11 wherein said bounding circuit comprises an amplifier to retard the on-bias of said pass transistor independent of biasing control from said operational amplifier such that said droop current signal is constrained to a maximum current value based on the value of said bounding voltage signal and irrespective of continued increases in said reference current signal stemming from increases in the load current.

13. The bounded droop voltage circuit of claim 11 further comprising a voltage reference to generate said bounding voltage signal.

14. The bounded droop voltage circuit of claim 11 wherein said bounding voltage signal is derived from a supply voltage signal that also determines the absolute value of said second voltage signal such that the value of said bounding voltage signal moves in proportion to changes in said second voltage signal arising from changes in the supply voltage signal.

15. The bounded droop voltage circuit of claim 1 wherein said first circuit comprises:

a transconductance amplifier to generate said droop current signal in proportion to a differential voltage signal developed as a function of the load current; and

a resistor through which said droop current signal is sourced to generate a first voltage signal determined by the voltage drop across said resistor arising from said reference current.

16. The bounded droop voltage circuit of claim 15 wherein said second circuit comprises:

a comparator to generate a control signal based on comparing said first voltage signal with a threshold voltage signal;

a voltage divider circuit to provide the full value of a regulation voltage reference signal to a regulation control circuit of the power supply in a first mode, and to provide a determined fraction of the regulation voltage reference signal in a second mode, said voltage divider circuit thus acting as said limiting circuit;

a switch coupled to a terminal end of said voltage divider circuit to set said voltage divider circuit in one of said first and second modes responsive to said control signal from said comparator circuit;

said determined fraction of said regulation reference voltage signal establishing the amount of output voltage droop allowed by said bounded droop voltage circuit when said first voltage signal falls below said threshold voltage signal.

17. The bounded droop voltage circuit of claim 15 wherein said second circuit comprises:

a comparator to generate a control signal based on comparing said first voltage signal with a threshold voltage signal;

a resistor coupled at a first end to a regulation voltage reference signal, and coupled at a second end to a regulation control circuit input of the power supply;

a switched current source responsive to said control signal from said comparator to reduce the value of the regulation control voltage reference signal provided to the regulation control circuit of the power supply by an amount determined by the value of said resistor and the magnitude of the current signal generated by said current source when said first voltage signal falls below said threshold voltage signal.

18. The bounded droop voltage circuit of claim 17 wherein said switched current source comprises a trimmable current source responsive to a trim signal to set a desired value of said current signal, thereby establishing the amount of voltage droop applied to said regulated output voltage signal by said power supply when said first voltage signal falls below said threshold voltage signal.

19. A power supply circuit comprising:

a control circuit to regulate an output voltage signal provided to a load powered by said power supply circuit at a first voltage level based on the relative values of a feedback signal derived from the output voltage signal and a reference signal corresponding to the first voltage level; and

a bounded droop voltage circuit to droop the output voltage signal by an amount determined by a droop voltage signal generated by said bounded droop voltage circuit based on a load current provided to said load, said bounded droop voltage circuit comprising;

a first circuit to generate a droop current signal proportional to the load current; and

a second circuit to generate said droop voltage signal based on said droop current signal to cause the power supply circuit to reduce said output voltage signal by an amount corresponding to said droop voltage signal, said second circuit including a limiting circuit to bound said droop voltage signal to a maximum value independent of the load current.

20. The power supply circuit of claim 19 wherein said second circuit comprises a resistive circuit coupled at a first end to said first circuit to receive said droop current signal and coupled at a second end to said regulated output voltage signal, such that a regulation feedback voltage signal at said first end of said resistive circuit is the sum of said droop voltage signal which is developed across said resistive circuit and said regulated output signal.

21. The power supply circuit of claim 20 wherein said limiting circuit comprises a current limiting circuit to fix a maximum value for said droop current signal based on a bounding voltage signal provided to said current limiting circuit.

22. The power supply circuit of claim 20 wherein said limiting circuit comprises a voltage clamping circuit to fix a maximum value for said droop voltage signal developed across said resistive circuit.

23. The power supply circuit of claim 22 wherein said voltage clamping circuit comprises a clamping diode coupled in parallel with said resistive circuit.

24. The power supply circuit of claim 19 wherein said first circuit comprises a current source to generate said droop current signal in proportion to the load current.

25. The power supply circuit of claim 24 wherein said current source comprises:

a transconductance amplifier to generate a reference current signal proportional to a differential input voltage signal that is dependent upon the load current; and

an operational amplifier circuit to generate said droop current signal proportional to said reference current signal.

26. The power supply circuit of claim 25 wherein said current source further comprises gain setting resistors to set a current gain for said droop current signal relative to said reference current signal.

27. The power supply circuit of claim 26 wherein at least one of said gain setting resistors comprises a user-selectable resistor element to permit setting said current gain as desired.

28. The power supply circuit of claim 25 wherein said operational amplifier circuit comprises:

an operational amplifier with a first input terminal coupled to a first voltage signal determined by said reference current signal and a second input terminal coupled to a second voltage signal determined by said droop current signal; and

a pass transistor in a feedback loop of said operational amplifier to control said droop current signal responsive to an output signal of said operational amplifier such that a difference between said first and second voltage signals is minimized.

29. The power supply circuit of claim 28 wherein said limiting circuit comprises a bounding circuit to override control of said pass transistor by said operational amplifier when said second voltage signal reaches the value of a bounding voltage signal.

30. The power supply circuit of claim 29 wherein said bounding circuit comprises an amplifier to retard the on-bias of said pass transistor independent of biasing control from said operational amplifier such that said droop current signal is constrained to a maximum current value based on the value of said bounding voltage signal and irrespective of continued increases in said reference current signal stemming from increases in the load current.

31. The power supply circuit of claim 29 further comprising a voltage reference to generate said bounding voltage signal.

32. The power supply circuit of claim 29 wherein said bounding voltage signal is derived from a supply voltage signal that also determines the absolute value of said second voltage signal such that the value of said bounding voltage signal moves in proportion to changes in said second voltage signal arising from changes in the supply voltage signal.

33. The power supply circuit of claim 19 wherein said first circuit comprises:

a transconductance amplifier to generate said droop current signal in proportion to a differential voltage signal developed as a function of the load current; and

a resistor through which said droop current signal is sourced to generate a first voltage signal determined by the voltage drop across said resistor arising from said reference current.

34. The power supply circuit of claim 33 wherein said second circuit comprises:

a comparator to generate a control signal based on comparing said first voltage signal with a threshold voltage signal;

a voltage divider circuit to provide the full value of a regulation voltage reference signal to a regulation control circuit of the power supply in a first mode, and to provide a determined fraction of the regulation voltage reference signal in a second mode, said voltage divider circuit thus acting as said limiting circuit;

a switch coupled to a terminal end of said voltage divider circuit to set said voltage divider circuit in one of said first and second modes responsive to said control signal from said comparator circuit;

said determined fraction of said regulation reference voltage signal establishing the amount of output voltage droop allowed by said bounded droop voltage circuit when said first voltage signal falls below said threshold voltage signal.

35. The power supply circuit of claim 33 wherein said second circuit comprises:

a comparator to generate a control signal based on comparing said first voltage signal with a threshold voltage signal;

a resistor coupled at a first end to a regulation voltage reference signal, and coupled at a second end to a regulation control circuit input of the power supply;

a switched current source responsive to said control signal from said comparator to reduce the value of the regulation control voltage reference signal provided to the regulation control circuit of the power supply by an amount determined by the value of said resistor and the magnitude of the current signal generated by said current source when said first voltage signal falls below said threshold voltage signal, said switched current source thus acting as said limiting circuit.

36. The bounded voltage droop circuit of claim 35 wherein said switched current source comprises a trimmable current source responsive to a trim signal to set a desired value of said current signal, thereby establishing the amount of voltage droop applied to said regulated output voltage signal by said power supply when said first voltage signal falls below said threshold voltage signal.

37. A method o providing voltage droop in a regulated output voltage provided by a power supply while maintaining a lower bound on said regulated output voltage, the method comprising:

generating a droop current proportional to a load current;

generating a droop voltage based on said droop current to adjust said regulated output voltage provided to a load; and

bounding said droop voltage to a maximum value to establish an accurate lower bound for said regulated output voltage.

38. The method of claim 37 wherein generating a droop voltage based on said droop current comprises passing said droop current through a droop resistor coupled in series to said regulated output voltage to generate an output feedback signal that is offset above said regulated output voltage by the value of said droop voltage.

39. The method of claim 38 wherein clamping said droop voltage to a maximum magnitude irrespective of further increases in the load current to establish a well defined lower bound for said regulated output voltage comprises placing a voltage clamp across said droop resistor, said voltage clamp configured to limit said droop voltage to a desired maximum value.

40. The method of claim 37 wherein clamping said droop voltage to a maximum magnitude irrespective of further increases in the load current to establish a well defined lower bound for said regulated output voltage comprises limiting a current source providing said droop current to a maximum output current magnitude irrespective of any further increases in said load current.

41. The method of claim 40 wherein said current source comprises a variably biased pass transistor sourcing said droop current from a supply voltage, the method further comprising:

generating a bias voltage for said pass transistor proportionate to said load current; and

limiting said bias voltage to a maximum value corresponding to a maximum desired droop voltage irrespective of further increases in said load current.

42. The method of claim 37 wherein adjusting the relative values of a feedback signal associated with said regulated output voltage and a reference signal corresponding to an initial value desired for said regulated output signal based on said droop voltage comprises:

feeding back said regulated output voltage as a first signal; and

adding said droop voltage to said first signal to generate said feedback signal.

43. The method of claim 42 further comprising regulating said regulated output voltage based on comparing said reference signal to said feedback signal, said reference signal corresponding to the desired initial value for said regulated output voltage absent any droop voltage compensation.