电源是电子设备的重要组成部分，其性能的优劣直接影响着电子设备的稳定性和可靠性。随着电子技术的发展，电子设备的种类越来越多，其对电源的要求也更加灵活多样。BUCK DC/DC变换器由于电路结构简单、调整方便、可靠性高等优点，在降压式场合一直得到广泛的应用。 BCD工艺是将DMOS与低压BiCMOS工艺结合起来的一种新型工艺，具有功耗低、集成度高、驱动能力强等优点。本论文针对此优点应用专用集成电路的设计方法，根据BUCK DC/DC变换器的工作原理及电流模式的PWM控制技术，设计了一款基于BCD工艺的单片BUCK DC/DC变换器芯片。文中对该变换器芯片各功能模块，如基准电压电路、过热保护电路、偏置电路、误差放大电路、电压比较电路、锯齿波振荡发生电路、自举驱动电路、欠压保护电路、电流检测电路等进行了设计并给出了仿真验证结果。该芯片具有变频保护功能：正常工作时工作频率恒定；输出过载或短路时不仅工作频率急剧降低而且占空比也变小，大大降低了短路电流和短路损耗，同时也保证了用户系统的安全。当使能端的电压为低电平时，芯片处于关断状态，静态电流及静态功耗很小。通过对使能端的控制可方便地实现芯片的遥控、定时、开关控制等功能。该芯片只需外接少数元件就可构成一高性能的单片BUCK DC/DC开关电源，可广泛应用于分布式电源系统、电池充电器等。 通过对变换器芯片应用电路的Hspice仿真，验证了设计方案和理论分析的可行性和正确性，同时在芯片电路设计的基础上，应用台湾汉磊0.8μm BCD工艺设计规则完成了芯片版图的绘制，编写了DRC、LVS文件并验证了版图的正确性。所设计的基于BCD工艺的单片BUCK DC/DC变换器芯片达到了预期的要求。

Power supply is one of the important elements of the electronic equipment; its influence on the stability and reliability of electronic equipments is becoming stronger amd stronger. With the development of electronic technology, the type of electronic equipments is becoming more and more, therefore, the requirements for power supply are various. With advantages of simple structure, convenient regulation and high reliability, BUCK DC/DC converter is widely used in voltage step-down situation. BCD process is a novel one that combines DMOS and low voltage BiCMOS process together; its advantages are low power dissipation, high integrity and strong drive. According to design method of ASIC, operation principle of BUCK DC/DC converter and pulse width modulation technique of current mode, a monolithic BUCK DC/DC converter IC based on BCD process is designed, which is integrated with many function modules, such as band-gap reference voltage circuit, over-thermal protection circuit, error amplifier, voltage comparator, saw-tooth oscillator, bootstrap drive circuit, under voltage lockout circuit, current sensing circuit and over-current protection circuit, etc. all these circuit structures and operation principles are designed and simulated. This chip features its unique frequency conversion proection, which can reduce duty cycle and operation frequency so as to decrease short-circuit current and power dissipation and guarantee the safety of the power supply when output is short-circuited. When the EN pin is low voltage, the chip operates in shutdown mode and its static current and power dissipation is low, so it is easy to realize remote and timing control. This chip can constitute a BUCK DC/DC converter with a minimum number of external components; thus, it can be widely used in distributed power systems, battery chargers and pre-regulators for linear regulators. The feasibility and validity of design method and theory analysis are proved by the simulation results of the chip’s application circuit with Hspice offered by EDA tools. On the basis of circuits of each function module, layout of the IC is completed according to EPISIL BCD 0.8um process design rules, DRC and LVS documents are compiled to confirm the validity of the layout. The monolithic BUCK DC/DC converter IC based on BCD process in the thesis can realize the target expected.