Design Of Fast Transient Response High Frequency Buck Converter

Nowdays, the portable electric devices have been widely applied to different fields. And they make strict demand on energe efficiency. Therefore, the different working modes are often needed, which are corresponding to quite different load currents.In this case, to maintainthe operating voltage supplied by the switching mode power supply steady during mode switching, a good dynamic response for the power supply is demanded. It makes the design of fast transient response switching mode power supply becomes one of hot topics in research on portable device power supplies. In this thesis, a fast transient response high frequency buck converter was proposed. Different from the voltage control mode, the adopted peak current control mode offers better dynamic response. To ensure fast system response, the switching frequency is set to 5MHz to get a large enough system loop bandwidth. In the other hand, as the core module in dc-dc converter, the slew rate of the error amplifier directly determines the dynamic response of the system. Thus, the design of the high slew rate error amplifier becames the key to implement of fast system dynamic response. The thesis proposed a novel high slew rate error amplifier that introduces a special slew rate enhancement circuit. In comparison with traditional slew rate enhancement circuits, it could provide higher slew rate for error amplifier and thus brings better transient response to switching mode power supply.The fast transient response high frequency buck converter proposed in this thesis is designed in TSMC 0.35um CMOS process. The system and modules are simulated in Cadence Spectre environment. The input voltage of the buck converter is 1.2V to 6V, its output voltage is from 1V to 3V, and the switching frequency is set to 5MHz. The simulation results showed that the output ripple of the buck converter is about 2% and the system efficiency is about 80%. Meanwhile, the output load current is up to 500mA. In addition, the slew rate of the error amplifier is improved by 6 times due to the proposed slew rate enhancement circuit. The simulation results also showed that by applying the novel slew rate enhancement circuit to the fast transient time high frequency buck converter, the system transient time is reduced to about 20% that is much less than 40% of the traditional high slew rate error amplifier. It indicates that the proposed buck converter could provide a better transient response.