A constant on-time control buck converter using adaptive ramp compensation (ARC) was proposed. Two slope voltages were introduced to detect the falling slope of the inductor current. The compensation slope was adjusted through a negative feedback loop, so that the compensation slope followed the falling slope of the inductor current. Finally, the extra poles brought by slope compensation were fixed, making it easier to compensate the design. On this basis, the transient enhancement circuit was introduced to improve the load step response speed. Under 5 V output, when the load was stepped from 3 A to 100 mA, the output voltage overshoot was reduced by 150 mV, and the recovery time was shortened by 10 μs. When the load was stepped from 100 mA to 3 A, the output voltage undershoot was reduced by 130 mV, and the recovery time was shortened by 12 μs.