Design Of A Buck Converter Based On Constant On-time Control Mode

Currently, due to the rapid development of technology, portable electronics such as smart phone and tablet have been gaining popularity and becoming a necessary part of our life. Power supply as the motor of all the electronics, determines their performance life. Solving the power problem is the key to enhance the performance of electronics and save natural resource. Power supply can be classified into linear and switching power supplies. The former due to its low efficiency has being replaced by the latter. Switching power supply gains widespread application for its low power consumption, high conversion efficiency, low cost and so on. DC/DC converter is a vital part of switching power supply, which includes various circuit topologies, buck, boost, buck-boost, Cuk and so on. For its flexibility, it has been widely utilized in all kinds of electronic products including smart phone, tablet and digital cameras.Buck DC/DC converter of traditional control mode can be categorized into current mode and voltage mode, which both have error amplifier and loop compensation network, decreasing the loop bandwidth and harm system transient response. Nevertheless, Buck DC/DC converter of constant on-time mode does not need error amplifier and take the output voltage ripple as the PFM control signal to the input of the open loop loop comparator. Therefore, compared to traditional control mode, it boasts the advantages of simple system configuration, fast transient response.A Buck DC/DC converter adopting constant on-time control mode is proposed in this thesis. According to heavy or light load current, it has two working modes, one is continuous conduction mode(CCM), and the other is discontinuous conduction mode(DCM). This converter has a wide input voltage range of 4.2 V ~ 16 V, an adjustable output voltage range of 0.8 V ~ 13 V by external devices, an efficiency of 95% with heavy load and an efficiency of over 82% with light load. It integrates under voltage protection, short circuit protection, thermal protection, and over current protection, ensuring its performance.This thesis introduces the development of switching power supply, analyzes different kinds of topologies, and further discusses the function characteristics, system architecture and its performance, as well as sub circuits design of bandgap voltage reference, bias, over temperature protection and loop comparator. Simulation has been completed with 0.6μm HVCD model by Hspice. The simulation results prove that this converter has good transient characteristics and conversion efficiency.