Method for Operational Amplifier Output Clamping for Switching Regulators

• US 20060279268A1
• Filed: 06/10/2005
• Published: 12/14/2006
• Est. Priority Date: 06/10/2005
• Status: Abandoned Application

• Current Assignee: Advanced Analogic Technologies Incorporated (Skyworks Solutions Incorporated)
• Original Assignee: Advanced Analogic Technologies Incorporated (Skyworks Solutions Incorporated)
• Inventors: Yu, Tim Wen Hui
• Application Number:
  US11/160,161
• Publication Number:
  US 20060279268A1
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A switching regulator includes a feedback network that generates a voltage V_ea that is proportional to the difference between the output of the switching regulator and a reference voltage. A comparator is used to compare V_ea to a sawtooth voltage to generate a voltage V_pwm. The voltage V_pwm drives a high-side switching transistor that controls the output of the regulator. A first clamping transistor that provides a variable gain connection between the voltage V_ea and ground. As V_ea rises above a predefined level, the clamping circuit increases the connection between V_ea and ground, preventing V_ea from substantially exceeding V_t. As a result, transient performance of the regulator is improved.

Claims

1. A method for controlling a switching regulator that includes a high-side switching transistor, the method comprising:

generating a voltage V_ea that is proportional to the difference between the output of the switching regulator and a reference voltage;

generating a sawtooth voltage V_t that is proportional to the current passing through the high-side switching transistor;

modulating a variable gain connection between the voltage V_ea and ground as a function of V_ea to limit the degree to which V_ea is allowed to exceed V_t; and

comparing V_ea and V_t to generate a PWM signal to drive the high-side switching transistor.

2. A method as recited in claim 1 that further comprises:

modulating a variable gain connection between the voltage V_ea and the input voltage to the switching regulator as a function of V_ea to limit the degree to which V_ea is allowed to fall below V_t.

3. A method as recited in claim 1 in which the step or modulating a variable gain connection between the voltage V_ea and ground further comprises:

generating a voltage proportional to the difference between V_ea and a voltage generated by a current source; and

using the proportional voltage to control a transistor that connects V_ea to ground.

4. A method as recited in claim 2 in which the step or modulating a variable gain connection between the voltage V_ea and the input voltage to the switching regulator further comprises:

generating a voltage proportional to the difference between V_ea and a voltage generated by a current source; and

using the proportional voltage to control a transistor that connects V_ea to the input voltage to the switching regulator.

5. A circuit for controlling a switching regulator that includes a high-side switching transistor, the circuit comprising:

a first op amp that generates a voltage V_ea that is proportional to the difference between the output of the switching regulator and a reference voltage;

a current sensing circuit that that generates a sawtooth voltage V_t that is proportional to the current passing through the high-side switching transistor;

a first clamping transistor that provides a variable gain connection between the voltage V_ea and ground;

a second op amp that drives the first clamping transistor as a function of V_ea to limit the degree to which V_ea is allowed to exceed V_t; and

a third op amp that compares V_ea and V_t to generate a voltage V_pwm to drive the high-side switching transistor.

6. A circuit as recited in claim 5 that further comprises:

a second clamping transistor that provides a variable gain connection between the voltage V_ea and the input voltage to the switching regulator; and

a fourth op amp that drives the second clamping transistor as a function of V_ea to limit the degree to which V_ea is allowed to fall below V_t.

7. A switching regulator that comprises:

a high-side switching transistor;

a feedback network that generates a voltage V_ea that is proportional to the difference between the output of the switching regulator and a reference voltage;

a comparator that compares V_ea to a sawtooth voltage to generate a voltage V_pwm to drive the high-side switching transistor;

a first clamping transistor that provides a variable gain connection between the voltage V_ea and ground; and

a first op amp that drives the first clamping transistor as a function of V_ea to limit the degree to which V_ea is allowed to exceed V_t.

8. A switching regulator as recited in claim 7 that further comprises:

a second clamping transistor that provides a variable gain connection between the voltage V_ea and the input voltage to the switching regulator; and

a second op amp that drives the second clamping transistor as a function of V_ea to limit the degree to which V_ea is allowed to fall below V_t.