一款基于ACOT控制模式的降压型变换器XD7252的设计

发布时间：2018-01-01 02:33

本文关键词：一款基于ACOT控制模式的降压型变换器XD7252的设计　出处：《西安电子科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：随着互联网技术的飞速发展,便携式用电设备开始日益普及,电源作为这些电子产品不可缺少的关键部分,它的利用效率越来越受到人们关注。由于同一产品中的不同组件可能需要不同的供电电压,所以开关电源芯片的应用也越加普遍。同时随着数字芯片、微处理器应用日益普遍,对变换器而言,它们是一类在工作中非常容易发生变动的负载,负载电流的变化率较高,这就要求DC-DC变换器芯片能够具有极快速的负载瞬态响应速度。为了达到这些要求,人们开始研究和关注开关电源芯片的恒定导通控制模式,它具有极快速的瞬态响应。本论文首先对开关电源芯片的背景知识做了简单描述和介绍,接着对设计一款降压型DC-DC变换器所必需的基本原理和关键技术进行了详细的论述。通过分析设计了XD7252的整体结构和模块划分,制订相关模块的性能指标,接着对关键子模块进行了设计及仿真,最后对芯片的整体电路进行了仿真分析。本论文中采用ACOT控制模式,这种模式具有极快速的负载瞬态响应,但其平均工作频率还是受负载和输入电压的影响较大,故在芯片中设计了环路锁频模块,该模块通过检测实际的工作频率,将此频率转成电压后与预设的电压值相比较,利用比较的结果调整导通时间的长短,通过反馈回路使频率稳定在预设的范围之内,该设计思想可以很好的应用于其他恒定导通控制模式的芯片中。在恒定导通控制模式下使用陶瓷电容作为输出滤波电容时,容易产生次谐波振荡而引起系统的不稳定,本论文提出一种产生虚拟电感电流纹波的新结构,补偿了通常借助输出电容ESR生成的输出纹波电压信号,这种结构在不额外增加芯片引脚的情况下有效避免了次谐波振荡,增强了系统稳定性。本文设计的变换器XD7252采用0.18μm BCD工艺,利用Cadence软件下的HspiceS工具对其进行电路的设计和仿真验证。仿真结果表明,芯片的各项指标符合设计要求。
[Abstract]:With the rapid development of Internet technology, portable electrical equipment is becoming more and more popular. Power supply is an indispensable part of these electronic products. Because different components of the same product may need different power supply voltage, the application of switching power supply chip is more and more common. At the same time, with the digital chip. Microprocessor is becoming more and more popular. For converters, they are a kind of load which is easy to change in operation, and the change rate of load current is higher. This requires the DC-DC converter chip to have extremely fast load transient response speed. In order to achieve these requirements, people began to study and pay attention to the on-on-on-control mode of switching power supply chip. It has very fast transient response. Firstly, the background of switching power supply chip is briefly described and introduced in this paper. Then the basic principle and key technology of designing a step-down DC-DC converter are discussed in detail. The overall structure and module partition of XD7252 are designed and analyzed. Then the key sub-modules are designed and simulated. Finally, the whole circuit of the chip is simulated and analyzed. In this paper, the ACOT control mode is adopted. This mode has extremely fast load transient response, but its average operating frequency is still greatly affected by the load and input voltage, so the loop frequency locking module is designed in the chip. By detecting the actual working frequency, the module converts the frequency to the voltage and compares it with the preset voltage value, and adjusts the length of the conduction time by using the comparison results. The frequency is stabilized within the preset range by the feedback loop. The design idea can be well applied to other constant on-control mode chips. When the ceramic capacitor is used as the output filter capacitor in the constant on-on control mode. It is easy to produce sub-harmonic oscillation and cause the instability of the system. This paper proposes a new structure to generate virtual inductor current ripple, which compensates the output ripple voltage signal usually generated by output capacitance ESR. This structure can effectively avoid the sub-harmonic oscillation and enhance the stability of the system without adding additional chip pins. The converter XD7252 designed in this paper adopts 0.18 渭 m BCD technology. The circuit design and simulation are carried out by using the HspiceS tool of Cadence software. The simulation results show that each index of the chip meets the design requirements.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM46

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