Auto calibration method used in constant on-time switching converter

A controller used in a switching converter with constant on-time control, wherein the switching converter includes a main transistor, and is configured to convert an input voltage into an output voltage, the controller comprises:

• an oscillator configured to generate a periodical clock signal with a predetermined duty cycle;
• an on-time control circuit having a first input terminal, a second input terminal, a third input terminal and an output terminal, wherein the first input terminal is configured to receive a first voltage, the second input terminal is configured to receive a second voltage, and wherein based on the first and second voltage, the on-time control circuit generates an on-time control signal at the output terminal to determine the on-time of the main transistor;
• a logic circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to the output terminal of the on-time control circuit, the second input terminal is coupled to the oscillator to receive the clock signal, and wherein based on the on-time control signal and the clock signal, the logic circuit generates a switch control signal at the output terminal to drive the main transistor;
• and
• a duty cycle detection circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to the oscillator, the second input terminal is coupled to the output terminal of the logic circuit, the output terminal is coupled to the third input terminal of the on-time control circuit, and wherein the duty cycle detection circuit compares the duty cycle of the switch control signal with the duty cycle of the clock signal, and generates a calibration code signal at the output terminal to adjust circuit parameters of the on-time control circuit.

A switching converter with constant on-time control, comprising:

• a first transistor having a first terminal, a second terminal and a control terminal, wherein the first terminal is configured to receive an input voltage;
• a second transistor having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the second terminal of the first transistor, the second terminal is coupled to a reference ground;
• an inductor having a first terminal and a second terminal, wherein the first terminal is coupled to the second terminal of the first transistor and the first terminal of the second transistor, the second terminal is configured to provide an output voltage;
• an oscillator configured to generate a periodical clock signal with a predetermined duty cycle;
• an on-time control circuit having a first input terminal, a second input terminal, a third input terminal and an output terminal, wherein the first input terminal is configured to receive a first voltage, the second input terminal is configured to receive a second voltage, and wherein based on the first and second voltage, the on-time control circuit generates an on-time control signal at the output terminal;
• a logic circuit coupled to the oscillator and the output terminal of the on-time control circuit, wherein based on the on-time control signal and the clock signal, the logic circuit generates a switch control signal drive the first and second transistors;
• and
• a duty cycle detection circuit coupled to the oscillator, the logic circuit and the third input terminal of the on-time control circuit, wherein the duty cycle detection circuit compares the duty cycle of the switch control signal with the duty cycle of the clock signal, and generates a calibration code signal to adjust circuit parameters of the on-time control circuit.