Non-linear control techniques for improving transient response to load current step change

• US 7,863,875 B1
• Filed: 04/23/2008
• Issued: 01/04/2011
• Est. Priority Date: 04/23/2008
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Guo, Yigang, Carobolante, Francesco
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US12/108,435
• Time in Patent Office: 986 Days
• Field of Search: 323222-226, 323268-277, 323/282, 323285-288
• US Class Current: 323/275
• CPC Class Codes: H02M 3/1584 with a plurality of power processing stages connected in parallel

Abstract

A voltage regulator may be configured to detect variation in load current and control transient response when the load current has a high slew rate or varies at high repetition rates. A linear control circuit may be employed to control charging of an output capacitor and a load of the regulator. Upon detection of high load current step-up change at high slew rates, a non-linear control circuit may be activated. The fast load current step change may be detected by comparing an output voltage of the regulator to a feedback input of an error amplifier of the linear control circuit. The output of the error amplifier may be clamped to prevent output voltage ring-back when using the non-linear control circuit or to control load release dip. Output voltage overshoot may be controlled by turning OFF a top switch that charges the output capacitor before the inductor current becomes zero.

Claims

1. A method of operating a voltage regulator, the method comprising:

using a linear control circuit to control a switch of a voltage regulator to charge an output capacitor and provide power to a load;

detecting a step change of a load current drawn by the load from the regulator;

responding to the step change of the load current by clamping an output voltage of a voltage error amplifier of the linear control circuit to control transient response of the regulator to the step change of the load current.

2. The method of claim 1 wherein the step change results in the load current having a step size equal to or greater than a pre-determined non-linear control threshold.

3. The method of claim 1 wherein detecting the step change of the load current drawn by the load from the regulator comprises:

comparing an output voltage of the regulator with a feedback voltage at an input of the voltage error amplifier of the linear control circuit, the error amplifier generating a comparison signal based on a difference between the feedback voltage and a reference voltage.

4. The method of claim 1 wherein the clamping of the output of the voltage error amplifier of the linear control circuit turns OFF the switch when using a non-linear control circuit to control the switch.

5. The method of claim 1 wherein the clamping of the output of the voltage error amplifier of the linear control circuit to prevents output voltage load release dip.

6. The method of claim 1 further comprising:

turning OFF the switch before inductor current flowing through an output inductor of the regulator reduces to zero to prevent the output voltage from overshooting.

7. A voltage regulator comprising:

a first switch and a second switch;

a linear control circuit configured to control the first and second switches to control charging of a load and an output capacitor coupled to a load;

a non-linear control circuit configured to charge the output capacitor and a load upon occurrence of a step change of a load current drawn by the load;

a clamping circuit configured to adaptively clamp an output of an error amplifier of the linear control circuit, wherein the clamping circuit comprises a first buffer configured to receive the output of the error amplifier and output a reference error amplifier signal, a filter coupled to delay the reference error amplifier signal, and a second buffer configured to receive the delayed reference error amplifier signal and output the delayed reference error amplifier signal to a PWM comparator of the regulator.

8. The regulator of claim 7 further comprising:

a load current detector configured to compare an output voltage of the regulator with a feedback input of an error amplifier of the linear control circuit to sense the dynamic load current step change.

9. The regulator of claim 7 wherein the clamping circuit is configured to clamp the output of the error amplifier when the non-linear control circuit is activated or when the load release dip happens.

10. The regulator of claim 8 wherein the non-linear control threshold is pre-determined.

11. A method of operating a voltage regulator, the method comprising:

controlling switching of a pair of synchronously switched transistors by pulse width modulation (PWM) using a linear control circuit;

detecting step change of load current drawn by a load from the regulator; and

controlling transient response of the regulator to the step change of the load current by clamping an output of a voltage error amplifier of the linear control circuit to turn OFF a top switch of the synchronously switched transistors.

12. The method of claim 11 wherein detecting the step change of the load current drawn by the load from the regulator comprises:

comparing an output voltage of the regulator with a feedback voltage input of an error amplifier of the linear control circuit, the error amplifier generating a comparison signal based on a difference between the feedback voltage and a reference voltage.

13. The method of claim 11 wherein the error amplifier is coupled to a voltage loop of the regulator.

14. The method of claim 11 further comprising controlling transient response of the regulator to the step change of the load current using a non-linear control circuit.

15. The method of claim 11 further comprising:

switching an input to a PWM comparator of the linear control circuit depending on whether the synchronously switched transistors is controlled using the linear control circuit or a non-linear control circuit, the PWM comparator being coupled to a current loop of a current mode control loop of the regulator.