The aim of this paper is to present a superior transient response of a digital peak current mode dc-dc converter in order to address input voltage fluctuation. In the dc power feeding system, a quick response is important for not only load fluctuation but also input voltage fluctuation. Since the proposed peak current mode control method can detect the peak current in real time, the transient response can improve compared with the conventional digital voltage mode PID control. As a result, the convergence time and undershoot of output voltage is suppressed by more than 50%.