Stability methods and structures for current-mode DC-DC voltage converters

• US 8,552,706 B2
• Filed: 03/29/2011
• Issued: 10/08/2013
• Est. Priority Date: 03/29/2011
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Wu, Guoming
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): NASH, GARY A
• Application Number:
  US13/074,984
• Publication Number:
  US 20120249106A1
• Time in Patent Office: 924 Days
• Field of Search: 323/284, 323/285, 323/288
• US Class Current: 323/288
• 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 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

DC-DC voltage converter structures and methods are provided that employ first and second transistors which are switched to control currents through an inductor and a capacitor to thereby provide an output voltage substantially equal to a predetermined reference voltage. Preferably included is a voltage feedback loop in which an error voltage is fed back to a loop comparator and further included is a current feedback loop that provides to the comparator a first voltage ramp whose amplitude is proportional to the amplitude of the converter'"'"'s input current. The output signal of the comparator sets the duty cycles of the first and second transistors. In each converter period, the first and second transistors of the voltage converter respectively control, through the inductor, a first current with a rising slope and a second current with a falling slope. Finally, converter stability is enhanced by providing a second voltage ramp having a slope related to a fraction (e.g., ½) of the falling slope and then comparing the error voltage of the voltage feedback loop to the sum of the first and second voltage ramps.

Claims

1. A voltage converter system to thereby generate an output voltage at an output port in response to an input voltage at an input port, comprising:

a switching voltage converter arranged to switch through a first transistor a first current with a rising slope and subsequently switch through a second transistor a second current with a falling slope;

a voltage feedback circuit arranged to generate an error voltage in response to the difference between said output voltage and a reference voltage;

a current feedback circuit arranged to provide a feedback voltage ramp in proportional response to said rising slope; and

a controller configured to sum a compensation voltage ramp having a compensation rising slope with said feedback voltage ramp to provide a summed voltage ramp to compare with said error voltage to thereby control duty cycles of said first and second transistors;

wherein the compensation rising slope of said compensation voltage ramp is less than said falling slope.

2. The system of claim 1, wherein said compensation rising slope is between 30 and 70 percent of said falling slope.

3. The system of claim 1, wherein said compensation rising slope is one half of said falling slope.

4. The system of claim 1, wherein said first transistor is switched on for a controlled time period to obtain said output voltage and wherein said controller includes:

a current generator to provide a compensation current related to said controlled time period;

a capacitor to provide said compensation voltage ramp in response to said compensation current; and

a summer to provide said summed voltage ramp in response to said feedback voltage ramp and said compensation voltage ramp.

5. The system of claim 4, wherein said current feedback circuit includes:

a resistor coupled to said input port to sense said first current; and

a differential amplifier to provide said feedback voltage ramp in response to a voltage across said resistor.

6. The system of claim 1, wherein said first and second transistors are coupled together to form a switching node and said switching voltage converter further includes:

a capacitor coupled across said output port; and

an inductor coupled between said switching node and said capacitor.

7. The system of claim 1, wherein said first and second transistors are coupled together to form a switching node and said switching voltage converter further includes:

a capacitor coupled across said output port and coupled to said second transistor; and

an inductor coupled between said input port and said switching node.

8. The system of claim 1, wherein said first and second transistors are coupled between said input and output ports and coupled together to form a switching node and said switching voltage converter further includes:

a capacitor coupled across said output port; and

an inductor coupled to said switching node.

9. A voltage converter system to thereby generate an output voltage at an output port in response to an input voltage at an input port, comprising:

a switching voltage converter arranged to switch through a first transistor a first current with a rising slope and subsequently switch through a second transistor a second current with a falling slope;

a voltage feedback circuit arranged to generate an error voltage in response to the difference between said output voltage and a reference voltage;

a current feedback circuit arranged to provide a feedback voltage ramp in proportional response to said rising slope; and

a controller configured to sum a compensation voltage ramp having a compensation rising slope with said feedback voltage ramp to provide a summed voltage ramp to compare with said error voltage to thereby control duty cycles of said first and second transistors;

wherein said first transistor is switched on for a controlled time period to obtain said output voltage and wherein said controller includes;

a current generator to provide a compensation current related to said controlled time period;

a capacitor to provide said compensation voltage ramp in response to said compensation current; and

a summer to provide said summed voltage ramp in response to said feedback voltage ramp and said compensation voltage ramp;

wherein said current feedback circuit includes;

a resistor coupled to said input port to sense said first current; and

a differential amplifier to provide said feedback voltage ramp in response to a voltage across said resistor; and

wherein said capacitor has a capacitance C, said resistor has a resistance R, said rising slope has an amplitude that is a portion r of a maximum current I_max at said output port, k is a constant less than one, and said current generator is configured to provide said compensation current in accordance with the relationship;

10. The system of claim 9, wherein said constant k is substantially one half.

11. A voltage converter system to thereby generate an output voltage at an output port in response to an input voltage at an input port, comprising:

a switching voltage converter arranged to switch, for a controlled time period, through a first transistor a first current with a rising slope and subsequently switch through a second transistor a second current with a falling slope;

a voltage feedback circuit arranged to generate an error voltage in response to the difference between said output voltage and a reference voltage;

a current feedback circuit arranged to provide a feedback voltage ramp in proportional response to said rising slope;

a duty generator configured to obtain a controlled time period during which said first transistor is switched on;

a current generator coupled to provide a compensation current related to said controlled time period;

a capacitor coupled to provide, in response to said compensation current, a compensation voltage ramp having a compensation rising slope; and

a summer to provide, in response to said feedback voltage ramp and said compensation voltage ramp, a summed voltage ramp to compare with said error voltage to thereby control duty cycles of said first and second transistors;

wherein the compensation rising slope of said compensation voltage ramp is less than said falling slope.

12. The system of claim 11, wherein said current feedback circuit includes:

a resistor coupled to said input port to sense said first current; and

a differential amplifier to provide said feedback voltage ramp in response to a voltage across said resistor.

13. The system of claim 11, wherein said compensation rising slope is between 30 and 70 percent of said falling slope.

14. The system of claim 11, wherein said compensation rising slope is one half of said falling slope.

15. A method to generate an output voltage at an output port in response to an input voltage at an input port, comprising the steps of:

switching through a first transistor a first current with a rising slope and subsequently switch through a second transistor a second current with a falling slope;

with a voltage feedback circuit, generating an error voltage in response to the difference between said output voltage and a reference voltage;

with a current feedback circuit, providing a feedback voltage ramp in proportional response to said rising slope; and

summing a compensation voltage ramp having a compensation rising slope with said feedback voltage ramp to provide a summed voltage ramp to compare with said error voltage to thereby control duty cycles of said first and second transistors;

wherein the compensation rising slope of said compensation voltage ramp is less than said falling slope.

16. The method of claim 15, wherein said compensation rising slope is one half of said falling slope.

17. The method of claim 15, further including the steps of:

switching said second transistor on for a controlled time period to obtain said output voltage;

a current generator to providing a compensation current that is inversely proportional to said controlled time period;

with a capacitor, providing said compensation voltage ramp in response to said compensation current; and

summing said feedback voltage ramp and said compensation voltage ramp to provide said summed voltage ramp.