A Novel Capacitor Current Constant on-Time Controlled Buck Converter at 4-MHz Switching Frequency

Abstract

Ripple-based constant on-time (RBCOT) controlled buck converter is widely used in power conversion system, such as voltage regulator module (VRM) or point of load (POL), but it has instability problem caused by using the ceramic capacitor (low ESR) as its output capacitor. To solve this issue, this paper proposed a novel capacitor current constant on-time (C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> COT) controlled buck converter, and it can achieve both fast transient response and be stable even if using the ceramic output capacitor. Moreover, the proposed dynamic on-time generator and novel minimum off-time generator for faster response and smaller chip area are introduced. The proposed control methodology was realized with 0.18um CMOS, operated at 4-MHz switching frequency and performed transient responses of settling time=200ns and 100ns at load current whose slew rate=1.3A/500ns step-up and step-down, respectively, in measurement results. Total chip size is only 1140.87um*993.08um with pad ring.