| Summary: | 碩士 === 國立臺灣大學 === 電機工程學研究所 === 107 === V2 constant on-time (V2COT) controlled buck converter is widely used to power microprocessors and digital loads, but there is an instability issue when ceramic capacitors are used as the converter’s output capacitors. Various COT control schemes have been reported in the literature to address the instability issue. However, these reported schemes have problems of needing trade-off between stability and transient response.
To these issues, a capacitor current constant on-time (C2COT) scheme is proposed in this thesis for buck converters. This scheme not only does not have the instability issue when using ceramic output capacitors but also allowing the decoupling of the stability and the transient response of the converters. A small-signal model was developed to theoretical prove the above statements, and are proved in simulation. The proposed scheme has no instability issue with the ceramic output capacitor; also, stability and fast transient response can be achieved without trade-off. A dynamic on-time generator is also proposed to further improve transient response and achieve accurate on-time at the high switching frequency.
The proposed control scheme was implemented in a monolithic IC using 0.18μm CMOS process with 4-MHz switching frequency. The experiment shows that output voltage equaling to 1-Volt and near-optimal load transient responses with 800ns settling time and null-response for both load current step-up and step-down, respectively. Total chip size is only 1140.87 μm by 993.08 μm with pad ring.
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