This paper presents a novel high-efficiency and fast-transient current-voltage-dual-mode (CVDM) dc-dc buck converter using adaptive clock controller (ACC). The proposed CVDM control can stably switch the control method between current mode and voltage mode to improve the performance according to different situations. By using the ACC technique, the circuit can dynamically and smoothly adjust the switching frequency during the transient response to improve the undershoot, overshoot voltage, and recovery time. In this work, only an output inductor, capacitor, and feedback resistors are outside the system on chip (SoC). The transient recovery time and undershoot voltage are less than 5μs and 60mV, respectively, for the load current change from 50mA to 500mA. The maximum conversion efficiency is 95% at 100mA load current. Above 90% conversion efficiency can be achieved for load current from 30mA to 600mA. With the proposed techniques, the performance of the dc-dc converter is improved significantly.