AOT架构Buck变换器中保护电路的研究与设计

发布时间：2018-05-17 04:30

  本文选题：自适应导通时间 + 降压型变换器　； 参考：《西南交通大学》2017年硕士论文

【摘要】：近年来,手机、平板电脑等电子产品更新换代的速度越来越快,随着其性能的不断提升,它们对电源管理芯片在输出电压、功耗、安全性等诸多方面提出了更高的要求。在众多的电源管理芯片中,AOT(自适应导通时间)架构的Buck变换器以其简洁稳定的控制环路、快速的瞬态响应和相对稳定的工作频率正成为降压型电源管理芯片中的主流类型。电源管理芯片对电子产品中的电能进行转换,保证其安全性是至关重要。在所有电源管理芯片的故障中,发生过流、过温是最主要的两种情况,可能直接导致芯片被烧毁。为此,本文主要对AOT架构的Buck变换器中的过流保护电路和过温保护电路进行了研究。本论文首先对电源管理芯片及其保护电路的研究背景、近年来国内外的最新研究成果和发展趋势进行了简要的介绍,然后对电源管理芯片,尤其是AOT架构Buck变换器的工作原理进行了较为详细的论述。随后,本论文对适用于AOT架构Buck变换器的过流保护电路进行了深入研究,针对现有的过流保护电路中MOS管RDS电流检测中存在的过流保护阈值随温度变化较大的问题,本论文对传统MOS管RDs电流检测中过流比较器输入端的参考电压VREF进行了改进,用一个PMOS管的漏源电压VDS提供参考电压给过流比较器,取代了通常使用的基准电压源。这样使得温度对载流子迁移率μ以及两个MOS管的导通压降的影响相互抵消,得到了一个基本不随温度变化的过流保护阈值,始终把电感电流限制在3.2A以下。为了尽可能减小过流保护过程中电路的功耗,本论文还在限流方式中引入了打嗝模式(Hiccup Mode),在短时间过流时采取恒定输出电流的限流方式,一旦过流故障得到排除,输出电流能迅速恢复正常;在长时间过流时采取降低输出电流的限流方式,每隔一段时间重复进行一次软启动,大大降低了平均输出电流,降低了功耗。在过温保护电路的设计中,本论文用工作在亚阈值区的MOSFET取代通常使用的BJT来产生PTAT正温度系数电压和CTAT负温度系数电压,降低了保护电路的静态功耗至5uA。同时,在自偏置PTAT和CTAT电流源中对低压宽摆幅共源共栅电流镜进行了改进,用两个电阻为共源共栅电流镜的MOSFET提供偏置,在提高PTAT、CTAT电流源精度的同时进一步降低了所需的电源电压,HSPICE仿真得出该过温保护电路在1.5V-7V的电源电压下都能正常工作,不同电源电压下的过温保护阈值容差仅0.1275℃C。
[Abstract]:In recent years, the speed of upgrading electronic products such as mobile phones, tablets and so on is getting faster and faster. With the continuous improvement of their performance, they put forward higher requirements on the output voltage, power consumption, security and other aspects of power management chips. In many power management chips, AOT (adaptive on-time) architecture Buck converter is becoming the mainstream type of the step-down power management chip with its simple and stable control loop, fast transient response and relatively stable operating frequency. It is very important for power management chip to convert electric energy in electronic products to ensure its safety. In all the faults of power management chips, overcurrent and overheating are the two most important cases, which may directly lead to the chip being destroyed. In this paper, the overcurrent protection circuit and the over-temperature protection circuit in the Buck converter with AOT architecture are studied in this paper. In this paper, the research background of power management chip and its protection circuit, the latest research results and development trend at home and abroad in recent years are briefly introduced, and then the power management chip is introduced. Especially, the working principle of AOT Buck converter is discussed in detail. Then, the overcurrent protection circuit suitable for Buck converter with AOT architecture is studied in this paper. Aiming at the problem of overcurrent protection threshold of RDS current detection of MOS transistor in the existing over-current protection circuit, the threshold value of overcurrent protection varies greatly with temperature. In this paper, the reference voltage VREF of the input of the over-current comparator in the traditional MOS tube RDs current detection is improved. The reference voltage is provided to the over-current comparator by the drain voltage VDS of a PMOS tube, which replaces the reference voltage source commonly used. In this way, the effect of temperature on carrier mobility 渭 and on voltage drop of two MOS transistors is counteracted, and an over-current protection threshold is obtained, which limits the inductance current below 3.2A. In order to reduce the power consumption of the circuit in the process of over-current protection as much as possible, this paper also introduces the hiccup mode in the current limiting mode, and adopts the constant output current limiting mode in the short time overcurrent, once the over-current fault is eliminated. The output current can be restored to normal rapidly, and the current limiting mode is adopted to reduce the output current for a long time, and the soft start is repeated every other time, which greatly reduces the average output current and reduces the power consumption. In the design of over-temperature protection circuit, the PTAT positive temperature coefficient voltage and the CTAT negative temperature coefficient voltage are generated by replacing the usual BJT with the MOSFET working in the sub-threshold region. The static power consumption of the protection circuit is reduced to 5 UA. At the same time, the low voltage wide swing cascode current mirror is improved in self-biased PTAT and CTAT current sources. Two resistors are used to provide bias for the MOSFET of the common gate current mirror. The simulation results show that the over-temperature protection circuit can work normally under the power supply voltage of 1.5V-7V, and the threshold tolerance of over-temperature protection is only 0.1275 鈩，

本文编号：1899937