A new fast-response current-mode buck converter with improved I²-controlled techniques is presented in this paper. First, the proposed converter uses the improved I²-controlled techniques to design a new current-mode buck converter. The current-sensing circuit can fully sense the inductor current. The sensing current is divided into two paths; one is flown through the dynamic-acceleration circuit, and the other is transferred to hysteretic comparator to compare with dynamic-acceleration output. The I²-controlled techniques increase the bandwidth of the converter's closed-loop gain that will speed up the converter's transient response. Second, the converter uses the phase- frequency-controlled techniques to lock the switching frequency of the adaptive on-time generator of the proposed converter and reduce the difficulty of the output filter. Third, the circuit does not need slope compensation, so that it is very simple to implement. Fourth, the proposed buck converter was implemented with TSMC 0.35-μm CMOS 2P4M processes, which is a low-cost process. The experimental results show that the maximum load current can be up to 600 mA, the input voltage range is 2.6-4 V, the output voltage is regulated at 1.8 V, the maximum power efficiency is up to 90%, and the transient response times are 2.5 and 2.8 μs at rising and falling edges, respectively.