For controlling DC-DC converters, variable switching frequency controllers have the advantage of fast transient response since the switching cycles can instantaneously change during the transient condition. However, these control techniques generally suffer significant steady-state switching frequency variation when the input voltage and output voltage are varied. Such drawback complicates the design of input and output filters. Therefore, this paper presents a current mode adaptive on-time control scheme. The proposed controller can dynamically adjust the turn-on time of power switches according to the changes of input voltage and output voltage in steady-state operation and can change switching cycles instantaneously in transient operation. Through the proposed control scheme, the DC-DC converters can accomplish fast transient response with the capability of mitigating the switching frequency variation. Full chip simulation results are provided to verify the proposed method. Comparisons with other control techniques are also presented.