Constant on-time switching converter with adaptive ramp compensation and control method thereof

A switching converter comprising:

• a first switch having a first terminal, a second terminal and a control terminal, wherein the first terminal is configured to receive an input voltage;
• a second switch having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the second terminal of the first switch, 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 switch and the first terminal of the second switch, the second terminal is configured to provide an output voltage;
• an output capacitor coupled between the second terminal of the inductor and the reference ground;
• an on-time control circuit configured to generate an on-time control signal;
• a ramp compensation generator coupled to the inductor in parallel and configured to generate a compensation signal, wherein the ramp compensation generator includes a variable resistor and a ramp capacitor serially coupled to the variable resistor;
• a comparing circuit coupled to the ramp compensation generator, wherein the comparing circuit compares the sum of the compensation signal and a feedback signal indicative of the output voltage with a reference signal to generate a comparison signal;
• a logic circuit coupled to the on-time control circuit and the comparing circuit, wherein based on the on-time control signal and the comparison signal, the logic circuit generates a control signal with a duty cycle;
• a driving circuit coupled to the logic circuit, wherein based on the control signal, the driving circuit provides a first driving signal and a second driving signal respectively to the control terminals of the first switch and the second switch;
• and
• a feed forward circuit, wherein based on the input voltage or the control signal, the feed forward circuit generates a compensation control signal to adjust the variable resistor in the ramp compensation generator.

A method for controlling a switching converter, wherein the switching converter includes a first switch, a second switch, an inductor and an output capacitor, and is configured to convert an input voltage into an output voltage, the control method comprises:

• generating an on-time control signal;
• generating a compensation signal;
• comparing the sum of the compensation signal and a feedback signal indicative of the output voltage with a reference signal to generate a comparison signal;
• generating a control signal with a duty cycle based on the on-time control signal and the comparison signal;
• generating a first driving signal and a second driving signal based on the control signal to respectively drive the first switch and the second switch;
• generating a compensation control signal based on the duty cycle of the control signal;
• and
• adjusting the compensation signal in accordance with the compensation control signal, so the amplitude of the compensation signal can follow a critical value proportional to the difference between the duty cycle and the square of the duty cycle.