Buck converter with quasi-fixed-frequency constant on-time architecture and on-timing circuit

An on-timing circuit, wherein the on-timing circuit is configured for a buck converter with a quasi-fixed-frequency constant on-time architecture, and allowed to output a turn-off signal for turning off an upper power transistor of the buck converter, wherein the on-timing circuit comprises a current generation module, an inversion delay counteracting module, a capacitor, and a comparator,

• wherein an input end of the current generation module is coupled to a switch node of the buck converter, an output end of the current generation module is coupled to a ramp voltage node, the upper power transistor in the buck converter and an inductor are coupled at the switch node, and the current generation module is configured to generate a charging current in direct proportion to a voltage of the switch node after the upper power transistor is turned on;
• an input end of the inversion delay counteracting module is coupled to the ramp voltage node, an output end of the inversion delay counteracting module is coupled to a first end of the capacitor, the inversion delay counteracting module is configured to generate a first delay for counteracting an inversion delay of the comparator according to a variable resistance unit and the capacitor, and a resistance value of the variable resistance unit is controlled by an input voltage of the buck converter;
• a second end of the capacitor is coupled to a ground terminal, and the capacitor is configured to be charged by the charging current after the upper power transistor is turned on;
• and
• a positive input end of the comparator is coupled to the ramp voltage node, a negative input end of the comparator is coupled to a first voltage, the comparator is configured to compare a ramp voltage corresponding to the ramp voltage node with the first voltage and generate the turn-off signal, and the first voltage is a reference voltage in proportion to an output voltage of the buck converter.