Boost开关电源型白光LED驱动芯片的研究与设计
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摘要
作为小尺寸液晶显示屏首选背光源的白光发光二极管,在手机、数码相机等便携电子设备上得到日益广泛的应用。而白光LED(Light Emitting Diode,发光二极管)驱动芯片,作为白光LED背光照明系统中的关键组成部分,其电路设计面临严峻挑战。这是因为目前便携电子设备小型化的趋势要求白光LED驱动芯片具备高效率、高可靠性和高功率密度等特点。
本文首先系统地研究了现有的白光LED驱动芯片设计技术,从中总结出三种不同的LED驱动设计方案。然后根据课题的设计要求选择了基于Boost DC/DC开关电源原理的驱动方案,并结合方案所涉及到的关键技术对芯片整体架构进行了设计。接下来,对芯片中的三个主要子模块——带隙基准源电路、斜坡补偿电路和数字接口电路的设计进行了详细讨论,并利用HSPICE仿真工具结合UMC 0.6μm BCD工艺库对所设计电路进行了仿真验证。在带隙基准电路的设计中,成功实现了一种新颖的带隙核结构,从而简化了电路架构,并同时达到了较高的电气性能;在斜坡补偿电路的设计中,创造性地提出了一种动态斜坡补偿电路,利用该电路可以简单有效地解决Boost DC/DC中容易出现的过补偿问题;数字接口电路的引入,使得所设计的白光LED驱动芯片具有数字调光功能,和传统PWM调光相比,该功能的实现能有效降低处理器的功耗。
最后,建立了典型应用电路,在选取合适的外部器件模型的基础上,用HSPICE对芯片进行了全局仿真。结果表明:在典型应用条件下,芯片启动时间在300μs以内,在10～40mA驱动电流范围内电源转换效率可达80%以上,能实现数字亮度调光和PWM调光功能,芯片的主要电气性能基本达到预期指标要求。
As the best choice of small-size LCD’s backlights, white LEDs have been used more and more in portable applications such as mobile phones and digital cameras. Meanwhile, white LED driver IC, which is the key component of LCD backlighting system, is facing critical challenge in its design. Because of the demand on small size for handheld devices, white LED driver IC should have the figures of high efficiency, high reliability and high power density.
In this thesis, with the in-deep study of current technique for white LED drivers, three main driving methods are proposed firstly. According to the application demands for this research, one of these methods is chosen for the design, which is based on Boost DC/DC switching power supply. And then, the key interrelated technique for Boost DC/DC is studied and the whole chip structure is constructed. The main subcircuits such as bandgap reference(BGR), ramp compensation and digital interface are designed and implemented with UMC 0.6μm BCD process, and the simulation results are also presented. A novel bandgap core structure is used in the BGR. Compared with conventional bandgap reference circuit, this bandgap structure is more immune to errors caused by current offset; a dynamic ramp compensation technology is used so that the over compensation problem in Boost DC/DC can be solved; the unique digital brightness control function can save processor power and battery life.
Finally, the whole chip simulation results by HSPICE are given: in typical application condition, the start-up time of the chip is only 300μs; the efficiency is above 80% when the LED current ranges from 10mA to 40mA; the digital brightness control and PWM dimming functions can be operated properly. In a whole, the results show that the main electrical characteristics of this chip matched the specification.
本文首先系统地研究了现有的白光LED驱动芯片设计技术,从中总结出三种不同的LED驱动设计方案。然后根据课题的设计要求选择了基于Boost DC/DC开关电源原理的驱动方案,并结合方案所涉及到的关键技术对芯片整体架构进行了设计。接下来,对芯片中的三个主要子模块——带隙基准源电路、斜坡补偿电路和数字接口电路的设计进行了详细讨论,并利用HSPICE仿真工具结合UMC 0.6μm BCD工艺库对所设计电路进行了仿真验证。在带隙基准电路的设计中,成功实现了一种新颖的带隙核结构,从而简化了电路架构,并同时达到了较高的电气性能;在斜坡补偿电路的设计中,创造性地提出了一种动态斜坡补偿电路,利用该电路可以简单有效地解决Boost DC/DC中容易出现的过补偿问题;数字接口电路的引入,使得所设计的白光LED驱动芯片具有数字调光功能,和传统PWM调光相比,该功能的实现能有效降低处理器的功耗。
最后,建立了典型应用电路,在选取合适的外部器件模型的基础上,用HSPICE对芯片进行了全局仿真。结果表明:在典型应用条件下,芯片启动时间在300μs以内,在10～40mA驱动电流范围内电源转换效率可达80%以上,能实现数字亮度调光和PWM调光功能,芯片的主要电气性能基本达到预期指标要求。
As the best choice of small-size LCD’s backlights, white LEDs have been used more and more in portable applications such as mobile phones and digital cameras. Meanwhile, white LED driver IC, which is the key component of LCD backlighting system, is facing critical challenge in its design. Because of the demand on small size for handheld devices, white LED driver IC should have the figures of high efficiency, high reliability and high power density.
In this thesis, with the in-deep study of current technique for white LED drivers, three main driving methods are proposed firstly. According to the application demands for this research, one of these methods is chosen for the design, which is based on Boost DC/DC switching power supply. And then, the key interrelated technique for Boost DC/DC is studied and the whole chip structure is constructed. The main subcircuits such as bandgap reference(BGR), ramp compensation and digital interface are designed and implemented with UMC 0.6μm BCD process, and the simulation results are also presented. A novel bandgap core structure is used in the BGR. Compared with conventional bandgap reference circuit, this bandgap structure is more immune to errors caused by current offset; a dynamic ramp compensation technology is used so that the over compensation problem in Boost DC/DC can be solved; the unique digital brightness control function can save processor power and battery life.
Finally, the whole chip simulation results by HSPICE are given: in typical application condition, the start-up time of the chip is only 300μs; the efficiency is above 80% when the LED current ranges from 10mA to 40mA; the digital brightness control and PWM dimming functions can be operated properly. In a whole, the results show that the main electrical characteristics of this chip matched the specification.
引文
[1]徐德平. LED照亮世界.中国科技奖励. 2005, 10: 44-47
[2]王海鸥.认识照明LED.中国照明电器, 2004, 2: 1-3
[3]艾朝霞,姬妍. LED照明光源前景展望.榆林学院学报, 2006, 16(4): 40-42
[4]平立.白光LED驱动综述.现代显示, 2006, 6: 44-48
[5] Falin Jeff. LCD显示屏的核心(WLED)供电.电子产品世界, 2004, 12: 140-142
[6] Michael. Day. LED Driver Considerations. http://focus.ti.com/lit/an/slyt084/ slyt084.pdf
[7]景卫兵,王宇华,张波.基于电荷泵的高效白光LED驱动电路设计.中国集成电路, 2005, 6: 48-51.
[8] National Semiconductor. LM2793 Low Noise White LED Constant Current Supply with Dual Function Brightness Control. http://www.national.com/search/search.cgi/ main?keywords=lm2793
[9] Maxim. 125mA 1x/1.5x Charge Pumps for 5 White LEDs in 3mm x 3mm TDFN. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4722
[10] Linear Technology. 100mA Ultralow Noise Charge Pump LED Supply with Output Current Adjust. http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003, C1039,C1133,P2132
[11]郑正一.升压式高亮度LED背光驱动电路设计.照明工程师社区, 2006, 4: http://www.5izm.net/article.php/6983
[12] National Semiconductor. LM3500 Synchronous Step-up DC/DC Converter for White LED Applications. http://www.national.com/search/search.cgi/main?key-words=LM35 00
[13] Maxim. High-Efficiency, 32V Step-Up Converters with TA Derating Option for 2 to 8 White LEDs. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4391
[14] Linear Technology . White LED Driver with Integrated Schottky in SC70 and 2mm×2mm DFN. http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003,C1042, C1031,C1061,P18152
[15] Texas Instrument. CONSTANT CURRENT LED DRIVER WITH DIGITAL AND PWM BRIGHTNESS CONTROL. http://focus.ti.com/docs/prod/folders/print/ tps61062.html
[16] Maxim. High-Voltage, 350mA, High-Brightness LED Driver with PWM Dimming and 5V Regulator. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4883
[17] Doug Varghn.白光LED驱动方案.电子产品世界, 2002, 6: 50-52
[18]吴富昌. LED与LED驱动器的搭配设计.国际照明与灯饰, 2006, 4: http://www. ys-lighting.net/wpscms/html/2006-4/20064201218551.htm.
[19]华伟.通信开关电源的五种PWM反馈控制模式研究.通信电源技术, 2001, 6: 8-12
[20]高原,邱新芸,汪晋宽.峰值电流控制开关电源斜坡补偿的研究.仪器仪表学报, 2003, 24(4): 118-120
[21] Pressman, A.开关电源设计(第二版).王志强(译).北京:电子工业出版社, 2005: 106-108
[22]周志敏,周纪海.开关电源实用技术——设计与应用.北京:人民邮电出版社, 2003: 55-58
[23]张占松,蔡宣三.开关电源的原理与设计(修订版).北京:电子工业出版社,2004: 178
[24] Acker Brian, Sullivan C R, Sanders S R. Synchronous Rectification with Adaptive Timing Control. in: Power Electronics Specialists Conference, 1995. PESC’95 Record., 26th Annual IEEE, 1995, 6: 88-95
[25]赵睿,张波.同步整流关键技术及其主要拓扑分析.电路与系统学报, 2004, 9(3): 100-104
[26]陆鸣.智能功率集成电路的核心技术——BCD集成工艺简述.见:华东地区第二届电源技术研讨会论文集.南京: 2002: 163-171
[27] Alan Hastings.模拟电路版图的艺术(影印本).北京:清华大学出版社, 2004: 417-420
[28] Tham K M, Nagaraj K. A Low Supply Voltage High PSRR Voltage Reference in CMOS process. IEEE Journal of Solid-State Circuits, 1995, 30: 31-35
[29] Pease, R. A. The design of band-gap reference circuits: trials and tribulations. in: IEEE Proceedings of the 1990 Bipolar Circuits and Technology Meeting. Minneapolis, MN, 1990. 214-218
[30]史侃俊,许维胜,余有灵. CMOS带隙基准电压源中的曲率校正方法.现代电子技术, 2006, 5: 113-116
[31]李浩亮,何乐年.一种高精度能隙基准电压电路.固体电子学研究与进展, 2005,25(1): 77-80
[32] Kevin Scoones, Munich. Voltage Reference Circuit with Increased Intrinsic Accuracy . US 6642777 B2. 2003
[33] Razavi B.模拟CMOS集成电路设计.陈贵灿,程军,张瑞智等(译).西安:西安交通大学出版社, 2000: 314
[34]杨汝.峰值电流控制模式中斜坡补偿电路的设计.电力电子技术, 2001, 35(3): 35-38
[35]赵辉,王洪君.具有最小开关损耗的DC-DC升压变换器.山东工业大学学报, 2000, 30(3): 292-296
[36] coilcraft. SPICE Model-ME3220. http://www.coilcraft.net/pdfs/spice_me-3220.pdf
[37] eCircuit Center. Capacitor Model. http://www.ecircuitcenter.com/Circuits/cmodel1/ cmodel1.htm
[38]钱恩学.高速PCB设计电容的应用. http://www.dz863.com/all-technology/EDA-PCB/ PCB-capacitances-2.htm
[39] TAIYO YUDEN. EMK212BJ105KD-T datasheet. http://www2.yuden.co.jp/hp/com/ main/php/ct_detail.php?lang=CS
[40] TAIYO YUDEN. EMK107BJ224KA-T datasheet. http://www2.yuden.co.jp/hp/com/ main/php/ct_detail.php?lang=CS
[41] microsemi. High Brightness White LED. www.microsemi.com/datasheets/upwledxx. pdf
[2]王海鸥.认识照明LED.中国照明电器, 2004, 2: 1-3
[3]艾朝霞,姬妍. LED照明光源前景展望.榆林学院学报, 2006, 16(4): 40-42
[4]平立.白光LED驱动综述.现代显示, 2006, 6: 44-48
[5] Falin Jeff. LCD显示屏的核心(WLED)供电.电子产品世界, 2004, 12: 140-142
[6] Michael. Day. LED Driver Considerations. http://focus.ti.com/lit/an/slyt084/ slyt084.pdf
[7]景卫兵,王宇华,张波.基于电荷泵的高效白光LED驱动电路设计.中国集成电路, 2005, 6: 48-51.
[8] National Semiconductor. LM2793 Low Noise White LED Constant Current Supply with Dual Function Brightness Control. http://www.national.com/search/search.cgi/ main?keywords=lm2793
[9] Maxim. 125mA 1x/1.5x Charge Pumps for 5 White LEDs in 3mm x 3mm TDFN. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4722
[10] Linear Technology. 100mA Ultralow Noise Charge Pump LED Supply with Output Current Adjust. http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003, C1039,C1133,P2132
[11]郑正一.升压式高亮度LED背光驱动电路设计.照明工程师社区, 2006, 4: http://www.5izm.net/article.php/6983
[12] National Semiconductor. LM3500 Synchronous Step-up DC/DC Converter for White LED Applications. http://www.national.com/search/search.cgi/main?key-words=LM35 00
[13] Maxim. High-Efficiency, 32V Step-Up Converters with TA Derating Option for 2 to 8 White LEDs. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4391
[14] Linear Technology . White LED Driver with Integrated Schottky in SC70 and 2mm×2mm DFN. http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003,C1042, C1031,C1061,P18152
[15] Texas Instrument. CONSTANT CURRENT LED DRIVER WITH DIGITAL AND PWM BRIGHTNESS CONTROL. http://focus.ti.com/docs/prod/folders/print/ tps61062.html
[16] Maxim. High-Voltage, 350mA, High-Brightness LED Driver with PWM Dimming and 5V Regulator. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4883
[17] Doug Varghn.白光LED驱动方案.电子产品世界, 2002, 6: 50-52
[18]吴富昌. LED与LED驱动器的搭配设计.国际照明与灯饰, 2006, 4: http://www. ys-lighting.net/wpscms/html/2006-4/20064201218551.htm.
[19]华伟.通信开关电源的五种PWM反馈控制模式研究.通信电源技术, 2001, 6: 8-12
[20]高原,邱新芸,汪晋宽.峰值电流控制开关电源斜坡补偿的研究.仪器仪表学报, 2003, 24(4): 118-120
[21] Pressman, A.开关电源设计(第二版).王志强(译).北京:电子工业出版社, 2005: 106-108
[22]周志敏,周纪海.开关电源实用技术——设计与应用.北京:人民邮电出版社, 2003: 55-58
[23]张占松,蔡宣三.开关电源的原理与设计(修订版).北京:电子工业出版社,2004: 178
[24] Acker Brian, Sullivan C R, Sanders S R. Synchronous Rectification with Adaptive Timing Control. in: Power Electronics Specialists Conference, 1995. PESC’95 Record., 26th Annual IEEE, 1995, 6: 88-95
[25]赵睿,张波.同步整流关键技术及其主要拓扑分析.电路与系统学报, 2004, 9(3): 100-104
[26]陆鸣.智能功率集成电路的核心技术——BCD集成工艺简述.见:华东地区第二届电源技术研讨会论文集.南京: 2002: 163-171
[27] Alan Hastings.模拟电路版图的艺术(影印本).北京:清华大学出版社, 2004: 417-420
[28] Tham K M, Nagaraj K. A Low Supply Voltage High PSRR Voltage Reference in CMOS process. IEEE Journal of Solid-State Circuits, 1995, 30: 31-35
[29] Pease, R. A. The design of band-gap reference circuits: trials and tribulations. in: IEEE Proceedings of the 1990 Bipolar Circuits and Technology Meeting. Minneapolis, MN, 1990. 214-218
[30]史侃俊,许维胜,余有灵. CMOS带隙基准电压源中的曲率校正方法.现代电子技术, 2006, 5: 113-116
[31]李浩亮,何乐年.一种高精度能隙基准电压电路.固体电子学研究与进展, 2005,25(1): 77-80
[32] Kevin Scoones, Munich. Voltage Reference Circuit with Increased Intrinsic Accuracy . US 6642777 B2. 2003
[33] Razavi B.模拟CMOS集成电路设计.陈贵灿,程军,张瑞智等(译).西安:西安交通大学出版社, 2000: 314
[34]杨汝.峰值电流控制模式中斜坡补偿电路的设计.电力电子技术, 2001, 35(3): 35-38
[35]赵辉,王洪君.具有最小开关损耗的DC-DC升压变换器.山东工业大学学报, 2000, 30(3): 292-296
[36] coilcraft. SPICE Model-ME3220. http://www.coilcraft.net/pdfs/spice_me-3220.pdf
[37] eCircuit Center. Capacitor Model. http://www.ecircuitcenter.com/Circuits/cmodel1/ cmodel1.htm
[38]钱恩学.高速PCB设计电容的应用. http://www.dz863.com/all-technology/EDA-PCB/ PCB-capacitances-2.htm
[39] TAIYO YUDEN. EMK212BJ105KD-T datasheet. http://www2.yuden.co.jp/hp/com/ main/php/ct_detail.php?lang=CS
[40] TAIYO YUDEN. EMK107BJ224KA-T datasheet. http://www2.yuden.co.jp/hp/com/ main/php/ct_detail.php?lang=CS
[41] microsemi. High Brightness White LED. www.microsemi.com/datasheets/upwledxx. pdf
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