Control circuit and associated method for switching converter

Patent metadata

Field	Value
Publication number	US-9774253-B2
Application number	US-201514789921-A
Country	US
Kind code	B2
Filing date	Jul 1, 2015
Priority date	Jul 2, 2014
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

A control circuit for switching converter has an ON signal generating circuit, a current sensing circuit, an OFF signal generating circuit, a logic circuit and an OFF threshold generating circuit. The ON signal generating circuit provides an ON signal based on a reference signal and a feedback signal. The current sensing circuit provides a current sensing signal based on a current flowing through a power switch of the converter. The OFF signal generating circuit provides an OFF signal based on an OFF threshold signal and the current sensing signal. The logic circuit provides a control signal based on the ON signal and the OFF signal. The OFF threshold generating circuit adjusts the OFF threshold signal based on the difference between a frequency of the switching signal and a preset frequency, so as to make the frequency of the switching signal substantially equal or larger than the preset frequency.

First claim

I claim:

1. A control circuit for a switching converter with at least a power switch, the control circuit comprising:
an ON signal generating circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive a reference signal, and wherein the second input terminal is configured to receive a feedback signal indicating an output voltage or a load current of the switching converter, and wherein based on a comparison result between the reference signal and the feedback signal, the ON signal generating circuit provides an ON signal at the output terminal, wherein the ON signal generating circuit comprises a first amplifier having a first input terminal, a second input terminal and an output terminal, and wherein the first input terminal is utilized as the first input terminal of the ON signal generating circuit, and wherein the second input terminal is utilized as the second input terminal of the ON signal generating circuit, and wherein the ON signal generating circuit further comprises a first comparator having a first input terminal, a second input terminal and an output terminal, and wherein the first input terminal is coupled to the output terminal of the first amplifier, and wherein the second input terminal is coupled to the second input terminal of the first amplifier, and wherein the output terminal is utilized as the output terminal of the ON signal generating circuit;
a current sensing circuit having an input terminal and an output terminal, wherein based on a current flowing through the power switch, the current sensing circuit provides a current sensing signal;
an OFF signal generating circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive an OFF threshold signal, and wherein the second input terminal is configured to receive the current sensing signal, and wherein based on a comparison result between the OFF threshold signal and the current sensing signal, the OFF signal generating circuit provides an OFF signal at the output terminal;
a logic circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive the ON signal, and wherein the second input terminal is configured to receive the OFF signal, and wherein based on the ON signal and the OFF signal, the logic circuit provides a switching signal at the output terminal, and wherein the switching signal is configured to control the power switch; and
an OFF threshold generating circuit having an input terminal and an output terminal, wherein the input terminal is configured to receive the switching signal, and wherein the output terminal is configured to provide the OFF threshold signal, and wherein the OFF threshold generating circuit adjusts the OFF threshold signal based on a difference between a frequency of the switching signal and a preset frequency, so as to make the frequency of the switching signal substantially equal or larger than the preset frequency; wherein
the OFF threshold generating circuit further comprises a clamping circuit configured to set a maximum value for the OFF threshold signal.

2. The control circuit according to claim 1 , wherein the switching converter is configured in a BUCK converter.

3. The control circuit according to claim 2 , wherein the power switch has a first terminal, a control terminal and a second terminal, and wherein the first terminal is configured to receive an input voltage, and wherein the control terminal is configured to receive the switching signal, and wherein the switching converter further comprises:
a low side switch having a first terminal, a control terminal and a second terminal, wherein the first terminal is coupled to the second terminal of the power switch, and wherein the second terminal is connected to ground; and
an inductor having a first terminal and a second terminal, wherein the first terminal is coupled to the second terminal of the power switch, and wherein the second terminal is configured to provide the output voltage.

4. The control circuit according to claim 1 , wherein the ON signal generating circuit comprises a first comparator having a first input terminal, a second input terminal and an output terminal, and wherein the first input terminal is utilized as the first input terminal of the ON signal generating circuit, and wherein the second input terminal is utilized as the second input terminal of the ON signal generating circuit, and wherein the output terminal is utilized as the output terminal of the ON signal generating circuit.

5. The control circuit according to claim 1 , wherein the OFF threshold generating circuit comprises a PLL circuit, wherein the PLL circuit is configured to receive a reference clock signal and the switching signal, and wherein the PLL circuit provides the OFF threshold signal based on a frequency difference between the reference clock signal and the switching signal.

6. The control circuit according to claim 1 , wherein the OFF threshold generating circuit comprises:
a first capacitor having a first terminal and a second terminal, wherein the second terminal is connected to ground;
a first current source;
a first switch having a first terminal, a second terminal and a control terminal, wherein the first terminal receives a first voltage via the first current source, and wherein the second terminal is coupled to the first terminal of the first capacitor;
a second switch having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the first terminal of the first capacitor, and wherein the second terminal is connected to ground;
a second capacitor having a first terminal and a second terminal, wherein the second terminal is connected to ground;
a second current source;
a third switch having a first terminal, a second terminal and a control terminal, wherein the first terminal receives a second voltage via the second current source, and wherein the second terminal is coupled to the first terminal of the second capacitor;
a third current source;
a fourth switch having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the first terminal of the first capacitor, and wherein the second terminal is coupled to ground via the third current source;
a third comparator having a first input terminal, a second input terminal and an output terminal, and wherein the first input terminal is coupled to the first terminal of the first capacitor, and wherein the second input terminal is configured to receive a second reference signal; and
a second logic circuit having a first input terminal, a second input terminal, a first output terminal and a second output terminal, wherein the first input terminal is coupled to the output terminal of the third comparator, and wherein the second input terminal is configured to receive the switching signal, and wherein the second logic circuit is configured to provide a plurality of control signals to control the first switch, the second switch, the third switch and the fourth switch.

7. The control circuit according to claim 6 , wherein the second logic circuit further comprise a pulse generating circuit, and wherein the pulse generating circuit is configured to generate a pulse signal the frequency of which is substantially the same as the frequency of the switching signal.

8. The control circuit of claim 6 , wherein the second logic circuit is configured to provide a first control signal and a second control signal, and wherein the first control signal is configured to control the first switch and the third switch, and wherein t

Assignees

• Chengdu Monolithic Power Sys

Inventors

• Xu Li

Classifications

• H02M3/156 Primary

  with automatic control of output voltage or current, e.g. switching regulators · CPC title

• H02M2001/0009

  Electricity · mapped topic

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title