一款高效率大功率4路白光LED驱动芯片XD1420的研究

发布时间：2018-05-09 16:31

本文选题：开关电源 + 高效率　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：LED由于其环保、节能、亮度高、发展空间大等优点,正逐渐成为LCD背光光源的理想选择。在背光LED驱动方式的发展过程中,与传统的电荷泵驱动方式相比,基于开关电源的串联升压式驱动方案更适合当今的LCD背光应用。首先BOOST架构保证了芯片能应用在锂电池供电的低压系统中,并且输出电压可根据LED串联个数自动调整,然后恒流式驱动方式保证了串联LED之间亮度的一致性,消除了制造工艺带来的偏差。而电荷泵由于其输出电压固定、并联驱动方式以及有限的带载能力,导致LED规模较小,亮度不均匀,只能应用在一些低成本、小尺寸的LCD背光应用中。本论文以“电源管理类集成电路关键技术理论研究与设计”项目为背景,结合背光LED驱动的需求,设计了一款高效率、大功率白光LED驱动电路XD1420,驱动类型属于升压型开关电源、恒流式驱动方式。电路设计基于某公司的0.18μmBCD工艺,仿真软件为Cadence、Hspice。XD1420属于典型的大功率LED驱动,电流最高可达350mA,为了增加应用的灵活性,LED电流设计为片外可编程。为了满足不同尺寸的LCD显示需要,LED电流可扩展到四个通道。系统的输出电流最大可达1.4A,应用时只需选择合适的外围器件参数即可保证系统在大范围负载内正常工作。芯片集成了完善的保护机制,确保每一个通道有足够的电压工作,并且一个通道在发生故障后会被移除,不会影响其它通道工作。每路电流之间经过了精确的匹配,误差可达到1%以内。四个通道的反馈电压的校正值随LED电流可调,有效地避免了固定的校正电压额外造成的功率损耗,实现了轻载高效,在60mA LED电流应用中,效率可达90%以上。为了满足控制亮度的一般需求,设计了模拟调光和PWM调光两种调光模式,亮度调节范围为最大亮度的0~100%。论文详细研究了系统的应用方案与电路关键功能的实现。首先研究了系统外围设计,讨论了器件选择的依据并展示出了器件参数的计算过程;其次对系统环路的稳定性进行了分析,基于“平均开关模型思想”对功率级电路进行建模,并对LED负载进行建模以获得LED的小信号模型,据此提出了一种补偿方法并给出了详细的补偿步骤和相关计算,确保了环路在各种电源输入及不同负载情况下的稳定性;然后研究了调光功能的实现,分析了PWM调光对LED电流的影响并提出了改进方法;最后针对系统启动时引入的电流过冲问题,提出了一种改善方法。所有电路模块均使用Hspice软件进行了仿真验证,并给出了相关的仿真波形,仿真结果证明芯片性能良好。
[Abstract]:Because of its advantages of environmental protection, energy saving, high brightness and large development space, LED is becoming an ideal backlight source for LCD. In the development of backlight LED drive mode, compared with the traditional charge pump drive mode, the series boost drive scheme based on switching power supply is more suitable for the application of LCD backlight nowadays. First, the BOOST architecture ensures that the chip can be used in the low voltage system powered by lithium battery, and the output voltage can be automatically adjusted according to the number of LED series, then the constant current drive ensures the consistency of the brightness between the series LED. The deviation caused by manufacturing process is eliminated. Because of its fixed output voltage, parallel drive mode and limited load capacity, the charge pump can only be used in low cost and small size LCD backlight applications because of its small scale and uneven brightness. In this paper, a high efficiency, high power white light LED drive circuit XD1420 is designed based on the project of "Research and Design of key Technologies of Power Management IC". The driving type belongs to boost switching power supply. Constant current drive mode. The circuit design is based on the 0.18 渭 mBCD process of a company. The simulation software is Cadence Hspice.XD1420, which is a typical high-power LED driver with a maximum current of 350 mA. in order to increase the flexibility of application, the mBCD current is designed as off-chip programmable. LCD current can be extended to four channels in order to meet different sizes of LCD display. The maximum output current of the system can be up to 1.4 A. in application, it is necessary to select appropriate peripheral device parameters to ensure the system to work normally in a wide range of loads. The chip integrates perfect protection mechanism to ensure that each channel has enough voltage to work, and one channel will be removed after failure, which will not affect the operation of other channels. After a precise match between each current, the error can reach less than 1%. The correction value of the feedback voltage of the four channels can be adjusted with the LED current, which can effectively avoid the power loss caused by the fixed correction voltage, and achieve light load and high efficiency. In the application of 60mA LED current, the efficiency can reach more than 90%. In order to meet the general requirement of brightness control, two dimming modes, analog dimming and PWM dimming, are designed. The application scheme of the system and the realization of the key function of the circuit are studied in detail. Firstly, the peripheral design of the system is studied, the basis of device selection is discussed and the calculation process of device parameters is shown. Secondly, the stability of the system loop is analyzed, and the power level circuit is modeled based on the idea of "average switch model". The LED load is modeled to obtain the small signal model of LED. Based on this, a compensation method is proposed and detailed compensation steps and relevant calculations are given to ensure the stability of the loop under various power input and load conditions. Then, the realization of dimming function is studied, the influence of PWM dimming on LED current is analyzed and the improvement method is put forward. All the circuit modules are verified by Hspice software, and the relevant simulation waveforms are given. The simulation results show that the chip has good performance.
【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】：2014
【分类号】：TM46;TM923.34

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