The purpose of this paper is to present a novel digital peak current mode dc-dc converter and its control characteristics. The proposed method can detect the peak current in real time. The proposed peak current detection circuit is composed of RC integrator and comparator as the A-D converter. The design of RC integrator has a large effect on regulation characteristics and the transient response of the proposed method. In this paper, the influence of circuit parameters of the RC integrator is clarified. As a result, it is confirmed that the proposed method shows a superior transient response by selecting optimal parameters. The convergence time and undershoot are suppressed by 67% and 34% compared with the conventional digital voltage mode control method, respectively.