Adaptive slope compensation for switching regulators

• US 7,479,778 B1
• Filed: 07/23/2007
• Issued: 01/20/2009
• Est. Priority Date: 11/07/2003
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: De Stasi, Frank John, Broach, Michael Eugene
• Primary Examiner(s): Hollington; Jermele M
• Application Number:
  US11/781,817
• Time in Patent Office: 547 Days
• Field of Search: None
• US Class Current: 324/117.00R
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: Y10S 323/901 Starting circuits

Abstract

A system, method, and apparatus are arranged to provide adaptive slope compensation in a switching regulator that includes an inductor. A control loop of the switching regulator is responsive to a ramp signal. A ramp generator that includes a capacitor circuit and a current source provides the ramp signal, where at least one of the current level of the current source and the value of the capacitor circuit are adjusted to vary the slope of the ramp signal. The adjustment of the ramp signal is responsive to at least one of: a set point for the output voltage of the switching regulator, a feedback voltage that is related to the output voltage, and a measured parameter associated with the inductor in the switching regulator. By dynamically adjusting the slope of the ramp signal, slope compensation is provided for a range of inductor values that can dynamically change during operation.

Claims

1. An apparatus for adjusting slope compensation in a switching regulator that includes an inductor, the apparatus comprising:

a first current source that is arranged to provide a first current (I₁) that is associated with the an output voltage (V_OUT) of the switching regulator, wherein the first current source is configured such that the first current (I₁) is proportional to V_REF·

K, wherein V_REF is proportional to the output voltage (V_OUT) of the switching regulator and K is a proportionality constant;

a second current source that is arranged to provide a second current (I₂) that is related to a measured value (V₁) associated with the inductor; and

a capacitor circuit that is arranged to receive a charging current to provide a ramp signal, wherein the ramp signal has a slope (m_e) that is related to the first and second currents via the charging current such that the slope is dynamically adjusted in response to changes in the output voltage (V_OUT) of the switching regulator and the measured value (V₁) associated with the inductor.

2. The apparatus of claim 1, further comprising a current divider circuit that is configured responsive to the first current (I₁) and the second current (I₁), and arranged to provide a divide current that is proportional to the ratio of the first current (I₁) to the second current (I₂) such that the charging current for the capacitor circuit is responsive to the divide current.

3. The apparatus of claim 2, the current divider circuit comprising:

a first transistor that is configured responsive to the first current (I₁), a second transistor that is configured to cooperate with the first transistor to provide a control signal, a third transistor that is arranged responsive to the control signal and the second current (I₂), and a fourth transistor that is arranged to cooperate with the third transistor to provide the divide current.

4. The apparatus of claim 1, wherein the second current source is configured such that the second current (I₂) is proportional to V₁·

K, wherein V₁ is proportional to the measured inductance value associated with the inductor and K is a proportionality constant.

5. The apparatus of claim 1, further comprising a third current source that is arranged to provide a third current that is proportional to an input voltage (V_IN) of the switching regulator, wherein the apparatus is arranged to subtract the third current from the first current (I₁) to provide a difference signal (DIFF) such that the slope (m_e) of the ramp signal is proportional to (DIFF·

K)/(V₁·

C), where K is a proportionality constant, and C is a value associated with the capacitance circuit.

6. The apparatus of claim 1, wherein the first current source is configured such that the first current (I₁) is proportional to V_REF·

K_R·

K_I, the second current source is configured such that the second current (I₂) is proportional to V₁·

K₁·

K_I, the slope (m_e) of the ramp signal is determined by the ratio of (V_REF·

K_R·

K_I) to (V₁·

K₁·

K_I·

C), wherein V_REF is proportional to the output voltage (V_OUT) of the switching regulator, V₁ is proportional to the measured inductance value associated with the inductor, K_R, K₁, and K_I are proportionality constants, and C is a capacitance value associated with the capacitance circuit.

7. The apparatus of claim 1, further comprising a third current source that is configured to provide a third current that is responsive to an input voltage (V_IN) of the switching regulator, wherein the first current source is coupled to the third current source and configured such that a difference is generated by the first current source and the third current source, wherein the first current source is configured such that the first current (I₁) is proportional to V_REF·

K_R·

K_I, wherein the second current source is configured such that the second current (I₂) is proportional to V₁·

K₁·

K_I, wherein the third current source is configured such that the third current is proportional to V_IN·

K_V·

K_I, wherein the difference is given as [(V_REF·

K_R·

K_I)−

(V_IN·

K_V·

K_I)] and the slope (m_e) of the ramp signal is proportional to a ratio of [(V_REF·

K_R·

K_I)−

(V_IN·

K_V·

K_I)] to (V₁·

K₁·

K₁·

C), wherein V_REF is proportional to the output voltage (V_OUT) of the switching regulator, V₁ is proportional to the measured inductance value associated with the inductor, K_R, K₁, and K_I are proportionality constants, and C is a capacitance value associated with the capacitance circuit.

8. The apparatus of claim 1, further comprising a feedback circuit that is arranged to provide a control voltage (V_REF) for the first current source in response to an output voltage (V_OUT) of the switching regulator.

9. The apparatus of claim 8, wherein the feedback circuit is a resistor divider circuit.

10. An apparatus for adjusting slope compensation in a switching regulator that includes an inductor, the apparatus comprising:

a first current source includes a first terminal configured to provide a first current (I₁) at the first terminal that is proportional to a first voltage (V_REF);

a second current source that includes a second terminal configured to provide a second current (I₂) at the second terminal that is proportional to a second voltage (V₁) that is proportional to a measured inductance value for the inductor;

a first current mirror circuit that includes a third terminal and a fourth terminal, wherein the third terminal is coupled to the first terminal and the first current mirror circuit is configured such that a first reflected current is provided at the fourth terminal that is proportional to the first current (I₁);

a current divider circuit that includes a fifth terminal, a sixth terminal and a seventh terminal, wherein the fifth terminal is coupled to the fourth terminal, the sixth terminal is coupled to the second terminal and the current divider is arranged to generate a third current at the seventh terminal that is proportional to a division of the first current (I₁) by the second current (I₂);

a second current mirror circuit that includes an eighth terminal and a ninth terminal, wherein the eighth terminal is coupled to the seventh terminal and the second current mirror circuit is configured such that a fourth current is provided at the ninth terminal that is proportional to the third current; and

a capacitor circuit that includes a tenth terminal that is coupled to the ninth terminal, wherein the capacitor circuit is arranged to receive the fourth current as a charging current to provide a ramp signal, wherein the ramp signal has a slope (m_e) that is proportional to the division of the first current (I₁) and the second current (I₂) via the charging current such that the slope is dynamically adjusted in response to changes in the first voltage (V_REF) and the second voltage (V₁) that is proportional to a measured inductance value for the inductor.

11. The apparatus of claim 10, the current divider circuit comprising a first transistor that is configured to respond to the first current (I₁), a second transistor that is configured to cooperate with the first transistor to provide a control signal, a third transistor that is configured to receive the control signal and the second current (I₂), and a fourth transistor that is arranged to cooperate with the third transistor and the second current source to provide the third current.

12. The apparatus of claim 10, the current divider circuit comprising:

a third current source includes a tenth terminal configured to provide a bias current (I_BIAS) at the tenth terminal;

a first transistor that includes a first collector that is coupled to the fourth terminal, a first base that is coupled to the tenth terminal, and a first emitter that is coupled to a first power supply terminal;

a second transistor that includes a second collector that is coupled to a second power supply terminal that is different from the first power supply terminal, a second base that is coupled to the fourth terminal, and a second emitter that is coupled to the tenth terminal;

a third transistor that includes a third collector that is coupled to the second power supply terminal, a third base that is coupled to the fourth terminal, and a third emitter that is coupled to the tenth terminal; and

a fourth transistor that includes a fourth collector that is coupled to the eighth terminal, a fourth base that is coupled to the tenth terminal, and a fourth emitter that is coupled to the first power supply terminal.

13. The apparatus of claim 10, wherein the first input signal (V_REF) corresponds to either a constant signal that represents a desired output voltage of the switching regulator, or a feedback signal that is directly proportion to an output voltage (V_OUT) of the switching regulator.

14. The apparatus of claim 10, further comprising a feedback circuit that is arranged to provide the first input signal (V_REF) in response to an output voltage (V_OUT) of the switching regulator.

15. The apparatus of claim 14, wherein the feedback circuit is a resistor divider circuit.

16. The apparatus of claim 10, wherein the first current source is configured such that the first current (I₁) is proportional to V_REF·

K, wherein V_REF is proportional to the output voltage (V_OUT) of the switching regulator and K is a proportionality constant.

17. The apparatus of claim 10, wherein the second current source is configured such that the second current (I₂) is proportional to V₁·

K, wherein V₁ is proportional to the measured inductance value associated with the inductor and K is a proportionality constant.

18. The apparatus of claim 10, further comprising a third current source that is coupled to the first terminal and arranged to provide a third current at the first terminal that is proportional to an input voltage (V_IN) of the switching regulator, wherein the apparatus is arranged to subtract the third current from the first current (I₁) to provide a difference signal (DIFF) such that the slope (m_e) of the ramp signal is proportional to (DIFF·

K)/(V₁·

C), where K is a proportionality constant, and C is a value associated with the capacitance circuit.

19. The apparatus of claim 10, further comprising a third current source that is coupled to the first terminal and configured to provide a third current that is responsive to an input voltage (V_IN) of the switching regulator, wherein the first current source is arranged in cooperation with the third current source such that a difference is generated at the first terminal, wherein the first current source is configured such that the first current (I₁) is proportional to V_REF·

K_R·

K_I, wherein the second current source is configured such that the second current (I₂) is proportional to V₁·

K₁·

K_I, wherein the third current source is configured such that the third current is proportional to V_IN·

K_V·

K_I, wherein the difference is given as [(V_REF·

K_R·

K_I)−

(V_IN·

K_V·

K_I)] and the slope (m_e) of the ramp signal is proportional to a ratio of [(V_REF·

K_R·

K_I)−

(V_IN·

K_V·

K_I)] to (V₁·

K₁·

K_I·

C), wherein V_REF is proportional to the output voltage (V_OUT) of the switching regulator, V₁ is proportional to the measured inductance value associated with the inductor, K_R, K_{1, and} K_I are proportionality constants, and C is a capacitance value associated with the capacitance circuit.

20. An apparatus for adjusting slope compensation in a switching regulator that includes an inductor, the apparatus comprising:

a first current source that is arranged to provide a first current (I₁) that is associated with the an output voltage (V_OUT) of the switching regulator;

a second current source that is arranged to provide a second current (I₂) that is related to a measured value (V₁) associated with the inductor, wherein the second current source is configured such that the second current (I₂) is proportional to V₁·

K, wherein V₁ is proportional to the measured inductance value associated with the inductor and K is a proportionality constant; and

a capacitor circuit that is arranged to receive a charging current to provide a ramp signal, wherein the ramp signal has a slope (m_e) that is related to the first and second currents via the charging current such that the slope is dynamically adjusted in response to changes in the output voltage (V_OUT) of the switching regulator and the measured value (V₁) associated with the inductor.