A novel adaptive voltage positioning (AVP) buck regulator using adaptive on-time (AOT) control targeted for applications with low-ESR output capacitors is proposed. In this work, AOT control is adapted to keep the system's switching frequency quasi-fixed or independent of the input supply voltage and the AVP mechanism is realized without the need to use conventional error amplifier compensator or extra current-sensing circuit. For ensuring the system's switching frequency not entering the range of acoustic frequency at light load, an AEAF (avoid entering acoustic frequency) circuit is also proposed. For comparison purpose, the implemented buck regulator can be set to operate under AVP or non-AVP mode. This work has been fabricated and verified with a standard 0.18μm CMOS technology. Experimental results show excellent transient recovery time of 4μs (under AVP mode), ±0.11% switching frequency variation (for the specified input voltage range), and 91% peak conversion efficiency.