Reduction of Equivalent Series Inductor Effect in Delay-Ripple Reshaped Constant On-Time Control for Buck Converter with Multi-layer Ceramic Capacitors

The time constant, which is the product of the output capacitor and its equivalent series resistance (ESR), limits the stability of conventional constant on-time control buck converter. To meet the expected requirements, SP-CAP is mostly used as output capacitor although it deteriorates the performance of converter. On the other hand, the multi-layer ceramic capacitors (MLCC) features low cost and small equivalent series resistance (ESR) and is widely used in commercial power management ICs. However, the stability often suffers from the sub-harmonic problem due to small time constant. This paper proposes a differential-zero compensator with the noise margin enhancement (DZC-NME) technique in constant on-time control buck DC-DC converter with ceramic output capacitor. The proposed DZC-NME technique not only eliminates the limit of large time constant but also tolerates the existence of equivalent series inductor (ESL) effect. Simulation result demonstrates the function and shows smaller output ripple of 10mV and high efficiency of 91 % with ESR which smaller than 1m Omega.