摘要
分析了基于National系列的半导体电源芯片．这一系列新型电源芯片大致可以分为两大类：低压差线性稳压器（LDO，low-dropout regulator）和开关稳压器．LDO是电流控制型稳压器，其输入-输出压差降至0．5～0．6V以下，相对传统的三端稳压器它具有更高的性能．它是一个自功耗很低的微型片上系统，具有极低的静态电流，稳压十分精确，外围应用电路十分简单方便．且它具有极低的自有噪音和较高的电源纹波抑制，具有快捷的使能控制功能，给它一个高（或者低）的电平可使它进入工作状态或睡眠状态，具有较好的性能／功率比，最适合用于需要低噪音和节电的电子设备．而开关稳压器的特点是高效节能，它代表着稳压电源的发展方向，现在已成为稳压电源的主流产品．开关电源内部的关键元器件工作在高频开关状态，本身消耗的能量很低，电源效率可达80％～90％，比普通线性稳压电源提高近一倍．此外，开关工作频率高，滤波电容、电感数值较小，因此开关电源具有重量轻，体积小等特点．由于功耗小，机内温升低，从而提高了整机的稳定性和可靠性，而且其对电网的适应能力也有较大的提高．这些芯片采用先进的制作工艺，体积极小，适用于各种便携设备，如移动手机、掌上／膝上电脑等．本文将分析芯片的各项输入输出参数、功能及典型应用电路．
This paper analyzes power products from National Semiconductor. They can be separated into two kinds approximately： low-dropout regulator （LDO） and switching regulator. LDO is current-controlling regulator. Its input to output voltage drop is reduced below 0. 5-0. 6V. It has better performance compared with traditional 3-terminal regulator. It is a mini-size systerrron-chip, which has low cost. It has very low quiescent current and its output voltage is very accurate. The application circuit is very simple, and its requirements of output capacitor and induetors are low. The LDO provides very low noise performance with low grand pin current in an extremely small package. It enables low voltage ripper. Also it has simple and fast enable control. A high （or low） level can make it working or shutting down. It has a high proportion of capability and power, and is very suitable for electronic equipments, which need low noise and low cost. The feature of switching regulator is high efficiency and saving power. It leads the developing direction of stabilized voltage power supplies, and it has been the main products in voltage regulators. Switching regulator utilizes field effect tube （FET） as a switch. It regulates the output voltage by Controlling duty ratio of the switch. Using power transistor as an example, voltage drop between the collector and the emitter is close to zero when FET fully turns on. And its current in the collector is zero when FET turns off. The key components in switching regulator are operated at high switching frequency, so the power consumption is very low, and the efficiency can achieve 80%-90%. These products use advanced architects and have very small package. It enables low voltage ripper on both the input and the output. With a very high switching frequency, the inductors and output capacitor can be physically small and low cost. The conductors hawe the features of small area and light weight. High efficiency is achieved through the use of FET. And because of low cost, the temperature increasing is light. It increases stability and reliability of the whole circuit. Because of different energy-storage elements, the switching regulator can be divided into two kinds. One is DC/ DC converter based on the inductor, the other is converter based on the capacitor. DC/DC converter based on the inductor has integrated switch FET. It utilizes an input and output inductor to storage energy. And it provides relatively high power converting efficiency in all DC/DC converting methods. But it needs more area compared with most linear methods and some methods based on the capacitor in the condition of the same output current. It is very suitable for the applications whose current is over 300 mA. And it can carry out voltage buck, boost or buck-boost topology. DC/DC converter based on the capacitor utilizes switching array, logical circuit and comparing controller to step up the voltage. And it uses capacitor to storage energy. The inductor is not needed in this kind of regulator. Its working frequency is very high, so mini-type capacitor （lμF） can be used. It needs small area and low using cost. Inner FET switching array controls ＂fast＂ voltage charge and discharge of the capacitor. So output voltage can be gained from input voltage by multiplying modulus such as 0. 5, 2, 3, 4 and so on. This method can achieve efficiency up to 90%. The converter can supply output voltage ±2 times as the input voltage only using outside capacitor. Its cost is mainly from the ESR （equivalent series resistance） of the capacitor and RDS（ON） of the inner switching transistor. And because the converter based on capacitor dose not need inductor, its radiation can be neglected. Battery charge management and LED light driver are also introduced in this paper. Take LP3947 as an example. It is a complete charge management system that safely charges and maintains a Li-Ion battery from either USB power source or AC adaptor. In USB mode, the LP3947 supports charging in low power or high power mode. Alternatively, the LP3947 can take charge from AC adaptor. In both USB and AC adaptor modes, charge current, battery regulation voltage, and End of Charge （EOC） point can be selected via I^2C interface. The charger also has under-voltage and over-voltage protection as well as an internal 5. 6 hr timer to protect the battery. And conductor such as LP3943 is an integrated device capable of independently driving LEDs. This device also contains an internal precision oscillator that provides all the necessary timing required for driving each LED. Two prescaler registers along with two PWM registers provide a versatile duty cycle control. The LP3943 contains the ability to dim LEDs in SMBUS/I^2C applications where it is required to cut down on bus traffic. They can do well in modern portable applications such as mobile telephone and palmtop/laptop computer and so on. The input and output parameter, function and typical application circuit will be analyzed in this paper.
出处
《南京大学学报（自然科学版）》
CAS
CSCD
北大核心
2007年第1期35-46,共12页
Journal of Nanjing University（Natural Science）
基金
国家自然科学基金(60472026)
