| 主权项 |
1. A controller used in a constant on-time switching converter, wherein the switching converter comprises a switching circuit having a high-side switch, a low-side switch, an inductor, and an output capacitor connected in parallel with a load, wherein the switching circuit is configured to convert an input voltage into an output voltage to drive the load, the controller comprises:
an on-time control circuit configured to generate an on-time control signal which is used to control the on-time of the high-side switch; an ultrasonic mode determination circuit configured to provide a flag signal indicating whether the switching converter enters into an ultrasonic mode, wherein when the switching frequency of the switching circuit approaches an audible range, the switching converter enters into the ultrasonic mode; a slope compensation module coupled to the ultrasonic mode determination circuit to receive the flag signal and configured to generate a slope compensation signal based on the flag signal; a comparison circuit coupled to the slope compensation module and the switching circuit, wherein the comparison circuit compares a feedback signal indicative of the output voltage of the switching circuit with a sum of a reference voltage and the slope compensation signal, and generates a comparison signal; and a logic circuit coupled to the on-time control circuit, the comparison circuit and the ultrasonic mode determination circuit, wherein based on the on-time control signal, the comparison signal and the flag signal, the logic circuit generates a high-side control signal for controlling the high-side switch and a low-side control signal for controlling the low-side switch; wherein when the switching converter enters into the ultrasonic mode, the low-side switch is turned ON by the logic circuit to discharge the output capacitor until the feedback signal decreases to reach the sum of the reference voltage and the slope compensation signal, and wherein the slope compensation signal has two parts: a normal slope compensation signal and an additional slope compensation signal, wherein the additional slope compensation signal is generated during the discharge of the output capacitor to eliminate the double pulses due to the ultrasonic mode and the value of the additional slope compensation signal increases during the discharge of the output capacitor. |
