降压型大电流LED驱动器的3A%203.5MHz%2042V%20转换器LT3477

大电流LED驱动器LT3477件廛用一_匿l匿l旨l围LT3477是一种内部有3A,42V开关管的多功能DC/DC变换器.它可组成升压型,降压型,升降压型及负压输出型,适用于多种应用领域.由于它既有传统的电压反馈环路.并有两个独特的电流反馈环路.所以它非常适用于以恒压,恒流方式驱动大电流LED.本文仅介绍它在驱动电流LED方面的应用.该器件主要特点:内部有两个检测电流的放大器;极宽的工作电压范围.从25V到25V;功率转换效率可高达91%;可以根据不同的输八电压条件.方便地组成降压型,升降压型及升压型写保护写保护特性允许用户对存储器进行保护.禁止对非易失性存储器阵列的编程.如果WP管脚与VCC相连.整个存储阵列被保护.只可对其进行读操作.此时CA T1161可以接收从地址和字节地址.在接收完第1个字节后.器件不发送应答信号来实现禁止对存储单元的编程.读操作除R/W位为1外.CAT1161读操作的起动与写操作完全一样.读操作包台3种方式:立即/当前地址读,选择,指定位置读和连续读.立即/当前地址读立即/当前地址读一般是和其它2种读操作结合起来使用.CA T1181芯片内部有1个地址计数器.它会保留接收到的最后1个地址并且自动加1.所以当使用当前地址读时.芯片读出的是前1个写入地址的下一个地址.当前◆方佩敏LED驱动电路;工作频率由外接电阻设定,其工作频率范围从200kHz到35MHz;可编程软启动;开关管的饱和电压(Vc臼)低.在25A时为O3V;小尺寸20管脚QFN封装【4mmx4mm) 或20管脚TSSOP封装工作温度范围一40℃～+85℃.个从器件地址(最低位为1.表示读).当收到应答信号时.就可以接收到需要读取位鼍的字节数据,接收完成之后发送1个停止信号.图8为选择H目定位置读的时序图.连续读连续读可以由选择读或者当前地址读起动.接收器件收到1个数据之后.不发送停止信号,而是发送1个应答信号.以示需要更多的数据.CA T1161接收到这个应答信号之后.自动把地址加1.然后继续发送该地址对应的数据.直到接收器件不发送应管信号.而是1个停止信号.需要注意的是. 地址读的操作步骤如下:发送起始信号和对应的从器件地址(最低位为1.表示读),在收到应答信号之后就可以开始接收数据.接收完数据后不应答.再发送一个停止条件.图7为立即/当前地址读的时序图.选择/指定位置读选择H定位置读是指定1个需要读取的地址单元.对其进行读取.其操作步骤是首先给出1个启动信号,然后给出从器件地址(最低位为0.表示写).在接收到应答信号之后发送1个指定的器件内部地址(地址低8位),然后等待应答.当应答到来的时候不发送停止信号而是发送1个启动信号和1 CA T1161在没有接收到应管信号而是接收到一个停止信号之后.就立即停止向外部送数据.连续读过程中,当地址计数器的值超过了器件的最大地址之后(2047),会自动溢出.从最低地址开始送数据.图9为连续读的时序图.IT总线程序设计在编写程序访问l℃总线器件时.必须严格按照总线标准进行,具体可参阅各器件的数据手册.有的单片机内部带FC总线接口,没有I2c总线接口的单片机可以使用模拟方法实现.有需要模拟f℃总线读写程序者可与我联系.我的邮箱该器件主要应用于高功率LED驱动器,分布式电源,恒压或恒流电源等.LT3477的两种封装的管脚排列如图1所示.各管脚功能如表1所示.1正电压输出时R1,R2设定(见图2)正电压输出时.V与FBP连接.FBN接分压器中间点,输出电压Vcur与R1,R2关系为V a:1235(1+RI/R2)2负电压输出时.FBN接地,FBP接R3,R4设定l见圈2)负电压输出时.FBN接地.FBP接R3,R4分压器中间点.输出电压V a,T与R3,R4关系为:V=一1235V(R3/R4)3.电流检测电阻R啦设定若I或Im端电压>625mV.电流检测电阻R&难接于I皆,与I洲之间或与l之间.I时鹾与RsB关系为:R&=1o0mWl表1若l或I端加的电压(625mY.则电流检测电阻Rg雌与『&推的关系为:R一=×百V~丽,,o.fnV裹2例如.若端加了>625mV,当R静瑾=050时,I摧为:1=100m广V=200mA若端加了309mV(V),则1为:Isea~=百30丽9mY=lOOmA在I删或l叫端改变vl删1或vl^ 的大小可在不改变R大小即可改变I涟或l的大小.这是较为方便的.如果在V.与GND之间接一个Ⅲ品联.卅靛舶234一..一元器件应用XLB3翮鹈献芯片用日误差小爬馥鲫擦驱动0秒:特有组定时◆谢炳兴交车,商一,xLB331A(B)芯片主要参数1电源VCC:45—6V.为保证在掉电后,不影响走时.XLB331A(B)在掉电后应在20脚维持电位器.其中间头接l删或l.则可方便地调节I大小.3频率设定电阻R'LT3477的开关频率与外接RT的关系如表2所示.囤3是一种1~,=330mA的LED驱动电路.根据圈3的参数可计算得:1)V∞值V a1.235I1+200~1Ok)=259笔者认为此电压过高.原文图中可能大于2.7V的电压(此时整个芯片耗电流为几个微安.一个3V的纽扣电池可用十几年).2时基:12MHz3段输出电流最大10MA.位电流输出最大05MA.均为灌电流.4三个按键实现所有设置及控制操作.支持按键按下连续操作5芯片寿命大于10万个小时.二,XLB331A(B),'I引脚功能见图1.1脚(RST)为开机复位.2脚【X_Q)为星期位输出.3脚(SS)为秒闪输出,4,5脚(XTAL1,XTAL2)为时钟引入端,6-9脚fM—G,_S,H_S,H—G)为分钟,小时个位,十位输出,10脚【GND)接电源负极,11脚【BULLJ为闹铃输出,12—18脚(DA—DG)为段输出.19脚(KEY)为按键扫描输入.20脚(VCC)按电源正极.三,xLB331A(B)的应用(见图2)1.时间及误差倍整设I按A键5秒后自动进入时间设置.且设置位闪烁.再按A键移位到相应的设置位.按B增加.按C减小.当按A使小时分钟位出现L一50时.为误差修整设置.按B,C键只对分钟数增加减小.当增加一个单位时.使日误差快13—1.7秒.当减小一个单位时.使走时日误差慢13—17秒【注:出厂修正系数50.在优质12M晶振情况下日误差小于0.2秒).当无任何键按下5秒的肖特基二极管.电容采用贴片式多层陶瓷电容即可.关系如图4所示.在O.2—0.3A的I时.其效率约87%.日rrI.I。

150KHz 40V 3A开关电流降压型DC-DC转换器XL1507特点⏹ 4.5V到40V宽输入电压范围⏹输出版本固定5V和ADJ可调⏹输出电压1.23V到37V可调⏹最大占空比100%⏹最小压差1.5V⏹固定150KHz开关频率⏹最大3A开关电流⏹内置功率三极管⏹高效率⏹出色的线性与负载调整率⏹EN脚TTL关机功能⏹EN脚迟滞功能⏹内置热关断功能⏹内置限流功能⏹内置二次限流功能⏹TO252-5L封装应用⏹LCD电视与显示屏⏹数码相框⏹机顶盒⏹路由器⏹通讯设备供电描述XL1507是一款高效降压型DC-DC转换器，固定150KHz开关频率，可以提供最高3A输出电流能力，具有低纹波，出色的线性调整率与负载调整率特点。

XL1507内置固定频率振荡器与频率补偿电路，简化了电路设计。

PWM控制环路可以调节占空比从0~100%之间线性变化。

内置使能功能、输出过电流保护功能。

当二次限流功能启用时，开关频率从150KHz降至50KHz。

内部补偿模块可以减少外围元器件数量。

图1.XL1507封装150KHz 40V 3A 开关电流降压型DC-DC 转换器 XL1507引脚配置EN GND SW VINFB 12345TO252-5LMetal Tab GND图2. XL1507引脚配置表1.引脚说明引脚号 引脚名称 描述1 VIN 电源输入引脚，支持DC4.5V~40V 宽范围电压操作，需要在VIN 与GND 之间并联电解电容以消除噪声。

2 SW 功率开关输出引脚，SW 是输出功率的开关节点。

3 GND 接地引脚。

4 FB 反馈引脚，通过外部电阻分压网络，检测输出电压进行调整，参考电压为1.23V 。

5 EN使能引脚，低电平工作，高电平关机，悬空时为低电平。

150KHz 40V 3A 开关电流降压型DC-DC 转换器 XL1507方框图EA1.23V ReferenceGNDFB3.3V 1.23VEA COMPOscillator 150KHz3.3V Regulator Start UpLatchCOMP2COMP1DriverThermal ShutdowninENSW220mV 200mV44m ΩCurrent LimitR2R1=2.5K5V R2=7.6KADJ R2=0 R1=OPENSwitch图3. XL1507方框图典型应用XL1507-5.0CIN 470uf 35VC1 105330uf 35VD1 L1 33uh/3A+12VLOAD13524GNDVINFBSWEN ON OFF 5V/3ACOUT 1N5820图4. XL1507系统参数测量电路（12V-5V/3A ）150KHz 40V 3A 开关电流降压型DC-DC 转换器 XL1507订购信息产品型号 打印名称封装方式包装类型 XL1507-ADJE1 XL1507-ADJE1 TO252-5L 2500只每卷 XL1507-5.0E1 XL1507-5.0E1TO252-5L2500只每卷XLSEMI 无铅产品，产品型号带有“E1”后缀的符合RoHS 标准。

摘至电子发烧友基于LM3478的50W DCDC升降压变换器设计方案现代电子技术发展很快，半导体供应商不断推出新器件，从而推动电子应用工程师的不断创新设计，以满足市场的日益需求。

本文介绍的即是基于客户的需求，应用美国国家半导体公司的新型电流型PWM芯片L通常称之为升降压变换器SEPIC的简单原理如下：当SW开通时，加在L1，L2上的电压均为Vin，此时Cp并在L2上，且有Cp上的电压与L2上的相等。

当SW关断时，L1中的电流继续沿着Cp、D1流向Cout输出到该电路是基于SEPIC拓扑、应用LM3478芯片按照客户的技术要求设计的。

在该电路中，考虑到适配器的体积及储能电感磁性材料的体积，选定工作频率Fs=250KHz。

计算储能电感L3、L4的电感量及磁芯选择首先由公式：D=Vout/(Vout+Vin)计算占空比。

由于最严酷条件下的电感纹波电流是在最大输入电压下，所以D=12/(12+60)≈0.167。

计算储能电感l3、L4：正常情况下，L4的大小在确保最小负载电流下使电感电流连续，且输出纹波满足指标要求。

为此，我们假定在20%最小负载电流下，允许有40%的峰-峰值纹波电流流过L4。

C1、C2为输入滤波，Q1、DZ1、DZ2、D1-1构成启动电源，L3、L4为储能电感，Q2为功率MOSFET，IC为PWM驱动芯片，R5为频率调整电阻，C3、C4、R2为反馈补偿，R3、R4为反馈分压电阻，R7为过电流取样电阻，C8、C9为SEPIC电容，R8、R9、C6、C7为吸收网络，D2为输出整流二极管，C10、C11、C12为输出滤波电容。

当然要想符合EMC要求，输入端还应该有共模电感，差模电感，及X、Y等安规电容。

L=Vdt/di;其中dt=1/FsD=1/(250103)0.167≈0.668，V为Vin在MOSFET开通时的值。

因此，有如下计算：L4=60(0.66810-6/0.4)=100.2μH。

CAT4201350 mA High Efficiency Step Down LED DriverDescriptionThe CA T4201 is a high efficiency step−down converter optimized to drive high current LEDs. A patented switching control algorithm allows highly efficient and accurate LED current regulation. A single RSET resistor sets the full scale LED string current up to 350mA from supplies as high as 36 V .The switching architecture of the CA T4201 results in extremely low internal power dissipation allowing the device to be housed in a tiny package without the need for dedicated heat sinking. The device is compatible with switching frequencies of up to 1 MHz, making it ideal for applications requiring small footprint and low value external inductors.Analog dimming and LED shutdown control is provided via a single input pin, CTRL. Additional features include overload current protection and thermal shutdown. The device is available in the low profile 5−lead thin SOT23 package ideal for space constrained applications.Features•LED Drive Current up to 350 mA•Compatible with 12 V and 24 V Standard Systems •Handles Transients up to 40 V•Single Pin Control and Dimming Function •Power Efficiency up to 94%•Drives LED Strings of up to 32 V •Open and Short LED Protection•Parallel Configuration for Higher Output Current •TSOT−23 5−lead Package•These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS CompliantApplications•12 V and 24 V Lighting Systems •Automotive and Aircraft Lighting•General Lighting, High Brightness 350 mA LEDsFigure 1. Typical Application CircuitSee Table 4 on page 6 for external component selection.TSOT−23TD SUFFIX CASE 419AEPIN CONNECTIONS AND MARKING DIAGRAMS (Top Views)TFYMDevice Package Shipping ORDERING INFORMATIONCAT4201TD−GT3TSOT−23(Pb−Free)3,000/Tape & ReelTF = Specific Device CodeY = Production Year (Last Digit)M = Production Month: (1−9, O, N, D)VBATSWCTRLGND RSET* Plated Finish: NiPdAu1TSOT−23Table 1. ABSOLUTE MAXIMUM RATINGSParameters Ratings UnitsVBAT, SW, CTRL−0.3 to +40VRSET−0.3 to +5VSwitch SW peak current1AStorage Temperature Range−65 to +160_CJunction Temperature Range−40 to +150_CLead Temperature300_CStresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected.Table 2. RECOMMENDED OPERATING CONDITIONSParameters Ratings UnitsVBAT voltage (Notes 1, 2) 6.5 to 36 (Note 1)VSW voltage0 to 36VAmbient Temperature Range−40 to +125_CLED Current50 to 350mA Switching Frequency50 to 1000kHz Functional operation above the stresses listed in the Recommended Operating Ranges is not implied. Extended exposure to stresses beyond the Recommended Operating Ranges limits may affect device reliability.1.The VBAT pin voltage should be at least 3 V greater than the total sum of the LED forward voltages in order to operate at nominal LED current.2.During power−up, the slew rate of the input supply should be greater than 1 m s for every 5 V increase of VBAT.Table 3. ELECTRICAL CHARACTERISTICS(V IN = 13 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified)) Symbol Parameter Conditions Min Typ Max UnitsI Q Operating Supply Current on VBAT pin0.41mAI SD Idle Mode Supply Current on VBAT pin CTRL= GND90m AV FB RSET Pin Voltage 2 LEDs with I LED = 300 mA 1.15 1.2 1.25VI LED Programmed LED Current R1 = 33 k WR1 = 10 k W R1 = 8.25 k W 270100300350330mAV CTRL−FULL CTRL Voltage for 100% Brightness 2.6 3.1V V CTRL−EN CTRL Voltage to Enable LEDs LED enable voltage threshold0.9 1.2V V CTRL−SD CTRL Voltage to Shutdown LEDs LED disable voltage threshold0.40.9VI CTRL CTRL pin input bias V CTRL= 3 VV CTRL= 12 V4020080m AR SW Switch “On” Resistance I SW = 300 mA0.9 1.5W T SD Thermal Shutdown150°C T HYST Thermal Hysteresis20°Ch Efficiency Typical Application Circuit86% Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product performance may not be indicated by the Electrical Characteristics if operated under different conditions.Figure 2. Input Operating Supply CurrentFigure 3. Idle Mode Supply Current(CTRL = 0 V)INPUT VOLTAGE (V)INPUT VOLTAGE (V)2220181614121080.20.40.60.81.02420161284050100150200Figure 4. CTRL Input Bias CurrentFigure 5. RSET Voltage vs. TemperatureCTRL VOLTAGE (V)TEMPERATURE (°C)12108642050100150200250 1.101.151.201.251.30Figure 6. RSET Voltage vs. CTRL Voltage Figure 7. LED Current vs. RSETCTRL VOLTAGE (V)RSET (k W )00.20.40.60.81.01.21.435302520151050100200300400Q U I E S C E N T C U R R E N T (m A )I D L E C U R R E N T (m A )C T R L B I A S C U R R E N T (m A )R S E T V O L T A G E (V )R S E T V O L T A G E (V )L E D C U R R E N T (m A )24Figure 8. Switching Frequency vs. InputVoltage (1 LED)Figure 9. Switching Frequency vs. InputVoltage (2 LEDs)INPUT VOLTAGE (V)INPUT VOLTAGE (V)10020030040050028242016128100200300400500600700Figure 10. Switching Frequency vs.TemperatureFigure 11. Switch ON Resistance vs. InputVoltageTEMPERATURE (°C)INPUT VOLTAGE (V)10020030040050024201816141210800.40.81.21.62.0Figure 12. Efficiency vs. Input Voltage (1 LED)Figure 13. Efficiency vs. Input Voltage(2 LEDs)INPUT VOLTAGE (V)INPUT VOLTAGE (V)7075808590951007075809095100S W I T C H I N G F R E Q U E N C Y (k H z )S W I T C H I N G F R E Q U E N C Y (k H z )S W I T C H I N G F R E Q U E N C Y (k H z )S W R E S I S T A N C E (W )E F F I C I E N C Y (%)E F F I C I E N C Y (%)2285Figure 14. Efficiency vs. LED CurrentFigure 15. LED Current Regulation vs.TemperatureLED CURRENT (mA)TEMPERATURE (°C)35030025020015010070758085909510012080400−40−10−8−4−224810Figure 16. LED Current vs. Input Voltage(1 LED)Figure 17. LED Current vs. Input Voltage(2 LEDs)INPUT VOLTAGE (V)INPUT VOLTAGE (V)2428201612840501001502002503003502428201612840050100150200250300350Figure 18. Switching Waveforms Figure 19. CTRL Power−up2 m s/div40 m s/divE F F I C I E N C Y (%)L E D C U R R E N T V A R I A T I O N (%)L E D C U R R E N T (m A )L E D C U R R E N T (m A )SW 5V/divInductor Current 200mA/divCTRL 5V/divLED Current 200mA/div−606Figure 20. RSET Transient ResponseFigure 21. Line Transient Response(10 V to 13 V)External Component SelectionTable 4 provides the recommended external components L and C2 that offer the best performance relative to the LED current accuracy, LED ripple current, switching frequency and component size.Table 4. EXTERNAL COMPONENT SELECTION1 LED2 LEDsLED Current (mA)L Inductor (m H)C2 Capacitor (m F)L Inductor (m H)C2 Capacitor (m F)≥15022 4.722 4.7< 15033 4.7472.24710NOTE:Larger C2 capacitor values allow to reduce further the LED ripple current if needed.Table 5. INDUCTOR SELECTION DEPENDING ON VBAT SUPPLY VOLTAGEVBAT Supply Voltage (V)Minimum Inductor L (m H)< 2622≥ 2633Table 6. PIN DESCRIPTIONPin Name Function1CTRL Analog dimming control and shutdown pin.2GND Ground reference.3RSET RSET pin. A resistor connected between the pin and ground sets the average LED current.4SW Interface to the inductor.5VBAT Supply voltage for the device.Pin FunctionVBAT is the supply input to the device. Typical current conduction into this pin is less than 1 mA and voltage transients of up to 40 V can be applied. To ensure accurate LED current regulation, the VBAT voltage should be 3V higher than the total forward voltage of the LED string. A bypass capacitor of 4.7 m F or larger is recommended between VBAT and GND.CTRL is the analog dimming and control input. An internal pull−down current of 20 m A allows the LEDs to shutdown if CTRL is left floating. V oltages of up to 40 V can be safely handled by the CTRL input pin.When the CTRL voltage is less than 0.9 V (typ), the LEDs will shutdown to zero current. When the CTRL voltage is greater than about 2.6 V, full scale brightness is applied to the LED output. At voltages of less than around 2.6 V, the LED current is progressively dimmed until shutdown.For lamp replacement applications, or applications where operation in dropout mode is expected, it is recommended that the CTRL pin voltage be derived from the LED cathode terminal.GND is the ground reference pin. This pin should be connected directly to the ground plane on the PCB.SW pin is the drain terminal of the internal low resistance high−voltage power MOSFET. The inductor and the Schottky diode anode should be connected to the SW pin. V oltages of up to 40 V can be safely handled on the SW pin. Traces going to the SW pin should be as short as possible with minimum loop area. The device can handle safely “open−LED” or “shorted−LED” fault conditions.RSET pin is regulated at 1.2 V. A resistor connected between the RSET pin and ground sets the LED full−scale brightness current. The external resistance value and the CTRL pin voltage determine the LED current during analog dimming. The RSET pin must not be left floating. The highest recommended resistor value between RSET and ground is 90 k W.Simplified Block DiagramFigure 22. CAT4201 Simplified Block DiagramCTRLBasic OperationThe CAT4201 is a high efficiency step−down regulator designed to drive series connected high−power LEDs. LED strings with total forward voltages of up to 32 V can be driven with bias currents of up to 350 mA.During the first switching phase, an integrated high voltage power MOSFET allows the inductor current to charge linearly until the peak maximum level is reached, at which point the MOSFET is switched off and the second phase commences, allowing the inductor current to then flow through the Schottky diode circuit and discharge linearly back to zero current.The switching architecture ensures the device will always operate at the cross−over point between Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). This operating mode results in an average LED current which is equal to half of the peak switching current.LED Pin CurrentThe LED current is set by the external RSET resistor connected to the regulated output of the RSET pin. An overall current gain ratio of approximately 2.5 A/mA exists between the average LED current and the RSET current,hence the following equation can be used to calculate the LED current.LED Current (A)^2.5V RSET (V)R SET (k W )Table 7 lists the various LED currents and the associated RSET resistors.Table 7. RSET RESISTOR SELECTIONLED Current (A)RSET (k W )0.10330.15210.20150.25120.30100.358.25APPLICATION INFORMATIONInput Voltage RangeThe minimum supply voltage required to maintain adequate regulation is set by the cathode terminal voltage of the LED string (i.e., the VBA T voltage minus the LED string voltage). When the LED cathode terminal falls below 3V ,a loss of regulation occurs.For applications which may occasionally need to experience supply “dropout” conditions, it is recommended that the CTRL input be used to sense the LED cathode voltage. The CTRL pin can either be tied directly to the cathode terminal (for Lamp Replacement) or connected via a pass−transistor for PWM lighting applications.Figure 23 shows the regulation performance obtained in dropout, when the CTRL pin is configured to sense the LED cathode voltage.123456CTRL VOLTAGE [V]L E D C U R R E N T [m A ]Figure 23. “Dropout” Configured LED Current(as shown in Typical Application on page 1)Inductor SelectionA 22 m H minimum inductor value is required to provide suitable switching frequency across a wide range of input supply values. For LED current of 150 mA or less, a 33 m H or 47 m H inductor is more suitable. Inductor values below 22m H should not be used.An inductor with at least 700 mA current rating must be used. Minor improvements in efficiency can be achieved by selecting inductors with lower series resistance.Table 8. SUMIDA INDUCTORSPart NumberL (m H)I Rated (A)LED Current (A)CDRH6D26−22022 1.00.35CDRH6D28−330330.920.35CDRH6D28−470470.80.35CDRH6D28−560560.730.35Capacitor SelectionA 10 m F ceramic capacitor C2 across the LED(s) keeps the LED ripple current within ±15% of nominal for most applications. If needed, a larger capacitor can be used to further reduce the LED current ripple. Any resistance in series with the LED (0.5 W or more) contributes to reduce the ripple current. The capacitor voltage rating should be equivalent to the maximum expected supply voltage so as to allow for “Open−LED” fault conditions. The capacitor value is independent of the switching frequency or the overall efficiency.A 4.7 m F ceramic input capacitor C1 is recommended to minimize the input current ripple generated on the ing a larger capacitor value further reduces the ripple noise appearing on the supply rail.If a constant capacitance is needed across temperature and voltage, X5R or X7R dielectric capacitors are recommended.Schottky DiodeThe peak repetitive current rating of the Schottky diode must be greater than the peak current flowing through the inductor. Also the continuous current rating of the Schottky must be greater than the average LED current. The voltage rating of the diode should be greater than the peak supply voltage transient preventing any breakdown or leakage.ON Semiconductor Schottky diode MBR0540 (40V ,500mA rated) is recommended. Schottky diodes rated at 400mA (or higher) continuous current are fine for most applications.NOTE:Schottky diodes with extremely low forward voltages (V F ) are not recommended, as they may cause an increase in the LED current.Dimming MethodsTwo methods for PWM dimming control on the LEDs are described below. The first method is to PWM on the control pin, the other method is to turn on and off a second resistor connected to the RSET pin and connected in parallel with R1.PWM on CTRL PinA PWM signal from a microprocessor can be used for dimming the LEDs when tied to the CTRL pin. The duty cycle which is the ratio between the On time and the total cycle time sets the dimming factor. The recommended PWM frequency on the CTRL pin is between 100Hz and 2kHz.Figure 24. PWM at 1 kHz on CTRL PinFigure 25. LED Current vs. Duty Cycle50100150200250300020406080100DUTY CYCLE [%]L E D C U R R E N T [m A ]Figure 26. Circuit for PWM on CTRLPWM on RSET PinAnother dimming method is to place in parallel to R1another resistor with a FET in series, as shown on Figure 27.R1 sets the minimum LED current corresponding to 0% duty cycle. The combined resistor of R1 and Rmax sets the maximum LED current corresponding to 100% duty cycle.Figure 27. Circuit for PWM on RSETA resistor value for R1 of less than 90 k W is recommended to provide better accuracy.Operation from High Supply Voltage Above 14 VFor operation from a supply voltage above 14 V , it is recommended to have a slew rate of 1 m s or more for every 5V increase in VBAT supply. When using a high supply voltage of 24 V , a 1 W or 2 W resistor in series with the supply,as shown on Figure 28, is recommended to limit the slew rate of the supply voltage. A 4.7 m F minimum ceramic capacitor is placed between the VBAT pin and ground. The combination of the series resistor R3 and input capacitor C1acts as a low pass filter limiting the excessive in−rush currents and overvoltage transients which would otherwise occur during “hot−plug” conditions, thereby protecting the CAT4201 driver.1 k WFigure 28. 24 V Application with 5 LEDsOperation from High Supply Voltage of 36 VWhen powering from a high supply voltage of 36 V , a 2W resistor in series with the supply is recommended, as shownon Figure 29, to limit the slew rate of the supply voltage.Inductor value should be 33 m H or higher.1 k WFigure 29. 36 V Application with 6 LEDsParallel Configuration for Driving LEDs Beyond 350mASeveral CA T4201 devices can be connected in parallel for driving LEDs with current in excess of 350 mA. The CAT4201 driver circuits are connected to the same LED cathode. Figure 30 shows the application schematic for driving 1 A into one LED with three CA T4201 connected in parallel. Each CA T4201 is driving the LED with a current set by its RSET resistor. The resulting LED current is equal to the sum of each driver current.CAT420111Figure 30. Three CAT4201 in Parallel for 1 A LEDOpen LED BehaviorIf the LEDs are not connected, the CAT4201 stops switching and draws very little current.At power−up with no load connected, the capacitor C2 is charged−up by the CA T4201. As soon as the bottom side of the capacitor (C2−) reaches 0 volt, as shown on Figure 31,the CA T4201 stops switching and remains in the idle mode only drawing about 0.4 mA current from the supply.Figure 31. Open LED ModeBoard LayoutIn order to minimize EMI and switching noise, the Schottky diode, the inductor and the output capacitor C2should all be located close to the driver IC. The input capacitor C1 should be located close to the VBA T pin and the Schottky diode cathode. The CA T4201 ground pin should be connected directly to the ground plane on the PCB. A recommended PCB layout with component location is shown on Figure 32. The LEDs are connected by two wires tied to both sides of the output capacitor C2. The LEDs can be located away from the driver if needed.Figure 32. Recommended PCB LayoutIn order to further reduce the ripple on the supply rail, an optional Pi style filter (C−L−C) can be used. A 10m H inductor rated to the maximum supply current can be used.TSOT −23, 5 LEAD CASE 419AE −01ISSUE ODATE 19 DEC 2008TOP VIEWSIDE VIEWEND VIEWNotes:(1) All dimensions are in millimeters. Angles in degrees.(2) Complies with JEDEC MO-193.SYMBOLθMINNOMMAXA A1A2b c DE E1e L 0º8ºL1L20.010.800.300.120.300.050.870.152.90 BSC 2.80 BSC 1.60 BSC 0.95 TYP0.400.60 REF 0.25 BSC1.000.100.900.450.200.50MECHANICAL CASE OUTLINEPACKAGE DIMENSIONSON Semiconductor and are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries.ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. ON Semiconductor does not convey any license under its patent rights nor the rights of others.© Semiconductor Components Industries, LLC, 2019PUBLICATION ORDERING INFORMATIONTECHNICAL SUPPORTNorth American Technical Support:Voice Mail: 1 800−282−9855 Toll Free USA/Canada Phone: 011 421 33 790 2910LITERATURE FULFILLMENT :Email Requests to:*******************onsemi Website: Europe, Middle East and Africa Technical Support:Phone: 00421 33 790 2910For additional information, please contact your local Sales Representative◊。

个干电池驱动两颗800m A L E D电路图目前很多工程师采纳L T C1872+A P3410设计驱动电路,只是本钱不低,本文介绍一低本钱的驱动电路.一节干电池是~,这样4个电池是~,驱动800M A L E D,L E D电压,2个就是.算到:输入功率=2**800m A/效率80%算=(实际高过80%效率,高过部份当作设计余量)时最大输入电流=/= 1.374A可以采用K B4313，实际应用电路如下图所示.L E D驱动芯片L T3477应用电路图L T3477的输入电压范围为至25V,适用于多种应用.它兼有传统的电压反馈环路和两个独特的电流反馈环路,以用作非常适用于驱动大电流L E D的恒定电流源和恒定电压源.L T3477用作升压型转换器、S E P I C或负输出.它还可配置成降压-升压模式或降压模式L E D驱动器,从而用于多种应用,甚至汽车电池等具有起伏电压输入的应用.L T3477的低V C E S A T开关在 2.5A时的电压为,工作效率高达91%.它在启动期间具有限制电感器电流的可编程软启动功能和在短路和电压瞬态期间爱惜L T3477的浪涌电流爱惜功能.扁平(0.75m m)4m m x4m m Q F N-20封装具有小占板面积和卓越的热性能.L T3477还采纳耐热增强型20引脚T S S O P封装和采纳4m m x4m m D F N-20封装的L T3477E U F和采纳T S S O P-16E封装的L T3477E F E均有现货供给.下图是升压线路参考设计线路,可4倍压升压驱动10W-20W负载,效率高达87%,在目前升压线路中还是较高的.凌特一直是器件领先企业,高可靠的代名词,当然价格也前沿.下图是升降压线路参考设计,这样设计比较合适在需要升降压应用时驱动L E D,比如锂电池需要驱动1p c s1-5W负载L E D和12V铅酸电池驱动3p c s3-15W负载L E D.L E D驱动芯片D D212要紧参数及应用电路图D D212电荷泵式驱动应用,只有一个电容器;内建的振动占空比调剂350K H z频率时钟.D D212采纳互补型金属氧化半导体集成电路C M O S 工艺制造;S O T25小体积封装比较适合手提式电子产品LE D应用设计;就只是一个听筒所占据小的区域;低功耗待机静态电流u A .大体参数:输入电压V~V倍压升压驱动1p c s L E D,电流最大400m A之内可设置,设计E N使能端口能够做开关利用.这款I C可以说是目前市场上面最简单的外围设计I C了,只需要三个外围器件,C1电源滤波、C e x t升压电容、R e x t反馈电流设置电阻.相信在手持式L E D产品中需要升压的线路中有较好的表现,以上的干电池供电、2节镍氢蓄电池、磷酸铁锂电池矿灯设计等产品比较适合.价格也比较优惠.L E D驱动芯片A T9933要紧特点及应用电路图S u p e r t e x公司推出A T9933,一款变频脉宽调制控制器集成电路,适用于采用低噪音升压拓扑控制L E D,可以自动降低和升高输入电压.A T9933额定可在达到125摄氏度下工作和符合A E C-Q100标准,使这款产品非常适用于汽车L E D照明应用.A T9933采用滞后性电流控制来调整输入和输出电流,对输入浪涌有优秀的免疫性而不需要复杂环路补偿和处部元件.输入和输出电流控制还提供内在短路和输入低压情况下保护.A T9933的宽输入电压范围和工作温度达到125度,使这款式产品在汽车应用驱动L E D灯的理想解决方案.随着汽车生产商认识到采用L E D的优点后,S u p e r t e x公司就在市场上推出最有效和最可靠的驱动器I C.上图书A T9933升压驱动线路参考设计,线路比较创新,红色线段是I C 工作上电电流示用意,蓝色是放电电流方向.双向电流I C都能够检测监控,并彼此牵制.超科一贯的外置M O S管的设计理念,能够设计较高功率L E D应用产品.上电:D2→L1→C1→D1→R c s1倍压充电,I C检测R c s1电阻电压判断充电是否完成.放电:C1→Q1→R c s2→L E D和D3→L2,因充电时C1电压是左正右负,电流从Q1这边流出,D1、D2均被反置,I C检测R c s2电压判断电流是否达到L E D预设值,达到驱动电流值后会关闭Q1,L2、D3、D1会继续维持电流存在,等待下一回合.上样品板参数:输入电压:V D C-16V D C;输出电压:28V最大;输出电流:350m A+/-5%;涟波输出:典型的5%;转变频率:430K H z V输入)300K H z V输入)500K H z V输入);效率:80%(在V输入);输出电压保护:33V钳位输出电压;输出短路保护:包括;极限浪涌电流350m A;L E D极性颠倒保护:-20V最大;最大输入界限:1.9A;P W M灰度调节:K H z .可配置起落压型高功率L E D驱动芯片M A X16831要紧参数及应用电路M A X16831是一款电流型、高亮L E D(H B L E D)驱动器,设计为通过控制2个外部n沟道M O S F E T来调节单串L E D的电流.M A X16831集成了宽范围亮度控制、固定频率H B L E D驱动器所需的全部组件.M A X16831可配置为降压型(b u c k)、升压型(b o o s t)或升/降压型(b u c k-b o o s t)电流调节器.带有前沿消隐的电流模式简化了控制回路的设计.内部斜率补偿可在占空比超过50%时保持电流环路的稳定.M A X16831工作于较宽的输入电压范围,并可承受汽车抛负载事件.多个M A X16831可相互同步或同步至外部时钟.M A X16831包含一个浮动亮度驱动器,驱动串联在L E D串的n 沟道M O S F E T实现亮度控制.使用M A X16831架构的H B L E D驱动器可在汽车应用中实现超过90%的效率.M A X16831还包括一个可源出 1.4A、吸收 2.5A电流(s i n k)的栅极驱动器,用于在高功率L E D驱动器应用中驱动开关M O S F E T,如车灯总成等.亮度操纵许诺宽范围的P W M调光,其频率可高达2k H z.在较低的调光频率下可实现高达1000:1的调光比.M A X16831提供带裸焊盘的32引脚薄型Q F N封装,工作于-40°C至+125°C汽车级温大体参数:宽输入范围:6V至76V;集成L E D电流检测差分放大器;可驱动n沟道M O S F E T;具有浮动亮度驱动能力;L E D电流精度:5%;200H z片上斜坡发生器,可同步至外部P W M亮度信号;可编程开关频率(125k H z至600k H z),可被同步;输出过压、负载开路、L E D短路、过酷爱惜;低至107m V L E D电流检测可提高效率;使能/关断输入,关断电流低于45µA.上图是美信M A X16831参考设计原理图,恒流部份和起落压部份是2个M O S管单独工作的,如此能够有效的提高灰度调剂能力,最多可驱动20p c s 1W L E D,若是是3W L E D功率可达60W.具体实际驱动情形我正在证明中,有消息当即会发布!美信公司的设计理念喜欢将M O S管外置,缺点是线路相对会复杂些,优点在应用设计中可以按需要适当调整,结合自己的实际能力设计出更高的功率.。

高性能LED背光驱动器高性能背光动AP3126 1.2MHz，0.6A 高达20V微功率输出升压转换器AP3126是一款小功率应用的恒定频率、5脚SOT封装，电流模式升压转换器，AP3126的开关频率为1.2MHz，允许使用较小的低成本电容和2mm或更小高度的电感。

内部软启动减小浪涌电流，延长电池寿命。

AP3126的输入电压低至2.5V，5V输入可以提供20V 高达100mA电流。

AP3126在轻载时采用自动脉冲频率模式。

AP3126特性还包括电流限制和过流保护以防止输出过载时损坏芯片。

AP3126采用纤小的SOT-23-5L封装小的SOT-23-5L封装。

内置1.8Ω功率MOSFET 40mA静态电流 OLED偏置 2.5V~5.5V输入电压 1.2MHz固定开关频率 内部0.6A 开关限流 LCD偏置输入 白光LED驱动 PDAs 数码相机可调输出电压 内部补偿高达20V输出电压轻载自动脉冲频率调制 超过85%效率采用SOT-23-5L封装AP3127升压型DC/DC LED 驱动器AP3127系列是固定振荡频率、恒流输出的升压型DC/DC转换器，非常适合于移动电话、PDA、数码相机等电子产品的背光驱动电路。

输出电压可达16V，3.2V输入电压可以驱动串联的四个LED，2.5V输入电压可以驱动两路并联LED(每路串联三个LED)。

通过改变CE脚上PWM信号的占空比可以控制LED的亮度。

内部集成有导通电阻只有1.8Ω的场效应管，外部可使用微型电感和电容，以缩小占用印制板的面积。

输入电压范围：2.5V至6.0V 输出电压范围：可达16V 启动参考基准电压：0.25V 振荡频率：10MHz 白光LED驱动 移动电话机 平板电脑 振荡频率：1.0MHz 输出导通电阻：1.8Ω转换效率：88%(驱动三个串联LED@Vin=3.6V ILED=20mA) 通过PWM信号控制LED亮度待机电流ISTB 10A(MAX) 数码相机MP3，PMP，PDA待机电流：ISTB=1.0uA(MAX) 负载电容：0.22uF(瓷介) Lx最大电流：300mAAP3127B升压型DC/DC LED 驱动器AP3127B系列是固定振荡频率、恒流输出的升压型DC/DC转换器，非常适合于移动电话、PDA、数码相机等电子产品的背光驱动电路。

LED驱动芯片资料美国美信集成产品公司白光LED驱动器MAX8678 白光LED在喇叭上整合应用IC PDF文档MAX1698，MAX1698A 便携式LCD屏背光源白光LED驱动应用IC PDF文档MAX1848 手机等小屏锂电池单色LED背光源恒流驱动IC PDF文档MAX1916 小体低压差式恒流驱动IC PDF文档MAX1910/MAX1912 锂电池1.5x/2x倍压式LED驱动器，最大120mA PDF文档MAX1570 锂电池1x/1.5x 倍压式LED驱动器，多路可PWM调光PDF文档MAX1984/MAX1985/MAX1986 白色LED超高效率恒流驱动PDF文档MAX1582/MAX1582Y可编程升压型2段恒流驱动IC PDF文档MAX1553/MAX1554 高效率, 升压到40V为 2 到 10 白色LED的转换器驱动PDF文档MAX1573 白色泵式 1 x/1.5 x 驱动器，小体积QFN型封装PDF文档MAX1561/MAX1599 高效率,升压型转换器26V驱动2到6颗白色LED驱动PDF文档MAX1574 180mA,1x/2x倍压白色泵式驱动IC 3毫米x3毫米TDFN小封装PDF文档MAX1583 白色的引导照相机-闪光推进转换器PDF文档MAX1575 白色LED驱动1x/1.5x电荷泵式光源指示PDF文档MAX1576 480mA白色LED 1x/1.5x/2x电荷泵式从背光照亮到照相机闪光灯应用PDF文档MAX1578/MAX1579 TFT屏与LED背光整合驱动应用IC PDF文档MAX8595Z/MAX8596Z 高效率，2.6-5.5V升压型32V，25mA，2-8颗LED驱动应用PDF文档MAX1577Y/MAX1577Z 1.2 A白色LED闪光灯应用IC PDF文档MAX8630W/MAX8630X 125mA 1x/1.5x电荷泵式为5颗白色LED小型TDFN封装PDF文档MAX8631X/Y LED电荷泵式1x/1.5x/2x 4毫米x 4毫米的二LDOs使QFN超薄封装PDF文档MAX8790 六线白色LED恒流驱动，适合笔记本等中尺寸LCD背光PDF文档MAX8607 为1.5A的1MHz PWM 推进转换器白色LED应用照相机闪光PDF文档MAX8647/MAX8648 超高效率电荷泵式6LED的/ RGB驱动应用，瘦小的QFN封装PDF文档美国美信集成产品公司高亮度LED驱动器MAX16800 高电压6.5-40V驱动35-350mA多颗LED应用驱动IC PDF文档MAX16801A/B PWM 控制器265VAC-85VAC 1A LED驱动器PDF文档MAX16802A/B PWM 控制器10.8VDC-24VDC 1A LED驱动器PDF文档MAX16803 高压、外置MOS管大电流，提供PWM亮度调节和5V稳压器PDF文档MAX16804 高电压5.5V-40V,350mA驱动和 PWM 控制暗淡PDF文档MAX16805/MAX16806EEPROM可设计的,高电压,350mA台灯等现场调光驱动应用PDF文档MAX16807/MAX16808 集成8通道LED驱动器，具有开关模式boost及SEPIC控制器PDF文档MAX16809/MAX16810 集成16通道LED驱动器，具有开关模式boost及SEPIC控制器PDF文档MAX16816可编程开关模式LED驱动器，大电流升降压LED驱动IC PDF文档MAX16818 1.5 MHz，30A高效率LED恒流驱动PDF文档MAX16819/MAX16820 2MHz高光亮LED驱动和5000:1灰度等级调节PDF文档MAX16821PDF文档MAX16823 高电压4.5-40V,3通道独立，5mA到70mA和外接BJT时可达到2A PDF文档MAX16824/MAX16825 3通道、高亮度LED (HB LED)驱动器，6.5V至28V输入电压PDF文档MAX7302 低电压LED驱动器，提供闪烁控制、PWM调节、瞬变检测及电平转换PDF文档MAX16831 可配置为降压型(buck)、升压型(boost)或升/降压型(buck-boost)电流调节器，输入6V至76V 大功率驱动恒流驱动PDF文档美国凌特公司白光背光及背光指示部分：LT1618 恒定电流/恒定电压 1.4MHz 升压型 DC/DC 转换器准确的输入/ 输出电流控制：在整个温度范围内的准确度达±5%；准确的输出电压控制：±1%；宽 VIN 范围：1.6V 至 18V输出最大36V/1.5A 电流PDF文档LT3591 白色LED用3x2mmDFN小体封装升压10颗LED背光应用PDF文档LTC3208 高电流软件可配置型多显示屏 LED 控制器1x/1.5x/2x 充电泵可提供高达 95% 的效率；高达 1A 的总输出电流；17 个电流源可用作主 (MAIN)、副 (SUB)、RGB、相机 (CAM) 和辅助 (AUX) LED 驱动器；可采用二线式I2C™ 接口来设置 LED 接通/关断、亮度等级和显示屏配置；采用跨接电容器边缘速率控制的低噪声恒定频率操作；自动充电泵模式切换；内部软起动功能限制了启动和模式切换期间的涌入电流；开路/短路 LED 保护；短路/热保护PDF文档LT3465 专为采用2 至 4 个白光 LED 和单节锂离子电池输入的彩色显示，背光源应用而优化。

一、概述SC2987是一款降压型PWM转换器，典型输出驱动电流为3.8A无需外加晶体管。

设计允许它可在8V～48V的宽输入电压下工作。

通过将COMP/EN脚逻辑电平拉低来控制外部关断功能，使其进入待机模式。

外部补偿使反馈控制具有良好的线性调整率和负载调整率，具有灵活的外围设计。

SC2987的特点之一是具有可编程的CV/CC模式控制功能。

CV（恒压）模式提供了一个稳定的输出电压，CC（恒流）模式提供了一个限流功能。

在电流检测放大器输入期间，CC电流值通过外部电阻设定。

SC2987适用于需要用到电流限制功能的DC/DC开关电源上。

该器件采用ESOP-8L封装，且工作时只需要很少的外围器件。

二、特性●电压输入范围：8V～48V●线电压Vout（Vref=1.2V）精度为±1%●CC/CV模式控制（恒流和恒压）●限流精度为±5%●输出短路保护●过压保护（超出输出电压的118%）●过温保护●内置软启动，启动时间12ms●固定频率120kHz●UVLO保护●占空比范围（0～90%）●单独的引脚进行外部补偿和关断控制●集成N-MOSFET●ESOP-8L封装三、应用●车充●便携式充电设备●高亮度照明设备●具有限流功能的多功能DC/DC变换器四、极限参数描述范围单位输入电压V VCC-0.3~50 VBST相对LX 0.3~7 VLX相对GND的直流电压-1~V VCC+1 VBST相对GND的直流电压-0.3~7 VFB,COMP相对GND的直流电压0.3~7 V ISEN-,ISEN+相对GND的直流电压0.3~9 V储存温度范围-65~150 ℃结点温度-20~150 ℃导热温度(焊接10s) 260 ℃人体模式ESD 2 KV机器模式ESD 200 V封装热阻ESOP-8L 60 ℃注意：如果器件工作条件超出上述各项极限值，可能对器件造成永久性损坏。

上述参数仅仅是工作条件的极限值，不建议器件工作在推荐条件以外的情况。

1Rev. 0DESCRIPTIONLT393536V, 4A Synchronous Buck LED Driver with Silent SwitcherDemonstration circuit 2987A is a 36V, 4A synchronous 2MHz buck LE D driver featuring the LT ®3935. This demonstration circuit powers one or two LEDs at 4A. DC2987A runs from an input voltage of 8V to 36V as built and can run down to 3.6V IN if UVLO is adjusted. It runs at 2MHz switching frequency. With Spread Spectrum Frequency Modulation (SSFM) turned on, it runs from 2MHz to 2.5MHz. An optional low-side NMOS PWM dim-ming MOSFET can be used for a high PWM dimming ratio. DC2987A features undervoltage lockout (UVLO) set at 7V with 0.7V hysteresis for turn-on. This Silent Switcher ® demo circuit features low emissions.The LT3935 has an input voltage range from 3.6V to 36V. It has internal, synchronous 5.8A, 40V switches for high power , and high efficiency with a single IC. It has an adjustable switching frequency between 200kHz and 2MHz. It can be synchronized (SYNC) to an external source or run with SSFM for low EMI.The LT3935 can be PWM dimmed for accurate brightness control. An optional low-side MOSFET can be driven from the PWM input source for high and accurate dimming ratio. However , LED – can be connected directly to GNDAll registered trademarks and trademarks are the property of their respective owners.for the least components. In this arrangement, PWM dim-ming has less range. Analog dimming is accomplished by driving the CTRL pin with a voltage below 1.5V to lower the LED sense voltage.Small ceramic input and output capacitors save space and cost. The open LED overvoltage protection uses the IC’s constant-voltage regulation loop to regulate the output to approximately 9V if the LED string is opened. Then a fault flag is asserted. The output current can be monitored through the ISMON output pin.The UVLO voltage, LED current, output voltage range, switching frequency, brightness control, and SSFM can all be adjusted with simple modifications to the demo circuit.The LT3935 data sheet gives a complete description of the device, operation and applications information. The data sheet must be read in conjunction with this demo manual for DC2987A. The LT3935JV is assembled in a 28-lead 5mm × 4mm LQFN package with a thermally enhanced GND.Design files for this circuit board are available .PERFORMANCE SUMMARYSpecifications are at T A = 25°CPARAMETERCONDITION MIN TYPMAX UNIT Input Voltage V IN RangeOperating I LED836V V IN Undervoltage Lockout (UVLO) Falling Operating V LED = 7.2V I LED = 4A7.0V V IN Enable Turn-On (EN) Rising 7.7V Safe Input Voltage V IN Range 036V Switching Frequency (f SW )R5 = 45.3kΩ, SSFM = OFF R5 = 45.3kΩ, SSFM = ON2.0 2.0 – 2.5MHz MHz LED Current I LED R1 = 25mΩ, 8V < V IN < 36V, V LED = 7.2V, V CTRL = 2V 4.0A LED Voltage V LED Range R7 = 1MΩ, R8 = 124kΩ 2.48.0VV Open LED Voltage V OUT R7 = 1MΩ, R8 = 124kΩ9.0V V Efficiency (100% PWM DC)12V V IN , 2MHz, 2 LEDs, SSFM = OFF91%%2Rev. 0BOARD PHOTOFigure 1. DC2987A Board Photo3Rev. 0QUICK START PROCEDUREFigure 2. Test Procedure Setup Drawing for DC2987ANOTE: Make sure that the voltage applied to V IN does not exceed 36V.The DC2987A is easy to set up to evaluate the performance of the LT3935. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below.1. With power off, connect a string of one or two LEDsthat runs with a forward voltage less than or equal to 8V at 4A to the LED + and LED – GND terminals.2. Connect the EN/UVLO terminal to GND.3. For always-on LED operation: Set JP3 to ON.4. With power off, connect the input power supply to theV IN and GND terminals.5. Turn the input power supply on and make sure the voltage is between 8V and 36V to start operation.6. Release the EN/UVLO-to-GND connection.7. Observe the LED string running at the programmedLED current.8. To change the brightness with analog dimming, sim-ply adjust the VR1 potentiometer or attach a volt-age source to the CTRL terminal and set the voltage between 0V and 2V. See data sheet for details. 9. To change brightness with external PWM dimming,set JP3 to EXT . Connect LEDs between LED + and LED – PWM terminals. Keep LED wire length to a minimum to achieve higher dimming ratios. Attach a 0V to 3V rectangular waveform with varying duty cycle to the PWM terminal.10. To enable spread spectrum frequency modulation,set JP2 to SSFM4Rev. 0Figure 3. DC2987A Efficiency vs Input Voltage with 2MHz and 2 LEDs at 7.4V LED 4A with SSFM OffFigure 4. DC2987A High Performance External PWM Dimming with LEDs Connected Between LED + and LED – PWM with SSFM Off, 12V IN and 7.4V LEDFigure 5. DC2987A 50% to 100% I LED Load T ransient with CTRL Input with SSFM Off, 12V IN and 7.4V LEDFigure 6. The LT3935 Can Achieve Dimming Ratios of 10000:1 at 100HzFigure 7. PWM Dimming Has Linear Behavior at High Dimming Ratios. Connect LED String to LED + and LED – PWM to Use the MOSFET for Highest Dimming RatioTEST RESULTSV IN = 12V , V LED = 7.4V , I LED = 4A f SW = 2MHz + SSFM ON100Hz EXTERNAL PWM DIMMINGWIRE LENGTH OF 15cm BETWEEN LED + AND LED – PWM5µs/DIVPWM 5V/DIVI LED 2A/DIV5Rev. 0EMISSION RESULTSFigure 8. Average and Peak Conducted Emissions Performance Using Current Method with CISPR25 Class 5 LimitsFigure 9. Average and Peak Conducted Emissions Performance Using Voltage Method with CISPR25 Class 5 LimitsFigure 10. Average and Peak Radiated Emissions Performance with CISPR25 Class 5 LimitsPARTS LISTITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBERRequired Circuit Components12C1, C2CAP., X7R, 0.1µF, 50V, 10% 0402, AEC-Q200MURATA, GCM155R71H104KE02D22C3, C22CAP., X7R, 1µF, 50V, 10% 0805, AEC-Q200MURATA, GCM21BR71H105KA03L32C5, C24CAP., X7R, 6.8µF, 16V, 10% 1206, AEC-Q200TDK, CGA5L1X7R1C685K160AC42C8, C11CAP., X5R, 2.2µF, 25V, 10% 0402, AEC-Q200MURATA, GRT155R61E225KE13D51C9CAP., C0G/NP0, 150pF, 25V, 5% 0402AVX, 04023A151JAT2A61C10CAP., X7R, 1000pF, 25V, 10% 0402AVX, 04023C102KAT2A71C12CAP., X7R, 0.1µF, 16V, 10% 0402AVX, 0402YC104KAT2A81C15CAP., X7R, 0.01µF, 16V, 10% 0603AVX, 0603YC103KAT2A91L1IND., 1µH WURTH ELEKTRONIK, 74438357010101R1RES., 0.025Ω, 1/2W, 1% 0805, AEC-Q-200SUSUMU, KRL1220E-M-R025-F-T1111R5RES., 45.3k, 1/16W, 1% 0402, AEC-Q200VISHAY, CRCW040245K3FKED121R6RES., 10k, 1/16W, 1% 0402, AEC-Q200VISHAY, CRCW040210K0FKED131R7RES., 1M, 1/16W, 1% 0402, AEC-Q200VISHAY, CRCW04021M00FKED141R8RES., 124k, 1/16W, 1% 0402, AEC-Q200VISHAY, CRCW0402124KFKED151U1IC., LT3935, LQFN-28, 5mm × 4mm ANALOG DEVICES, LT3935JV#PBFAdditional Demo Circuit Components160C6CAP., OPTION, ALUM. ELECT., SMD174C13, C14, C20, C23CAP., X7S, 10µF, 50V, 10% 1210, AEC-Q200MURATA, GCM32EC71H106KA03L180C17CAP., OPTION, 0402190C25, C26CAP., OPTION, 0603202FB1, FB2FERRITE BEAD, 120Ω, 0805MURATA, BLM21PG121SH1D210FB3, FB4, FB5, FB6FERRITE BEAD, OPTION, 0805221Q1XSTR., MOSFET, N-CH, 20V, 4.7A, SOT23-3NEXPERIA, PMV28UNEAR232R2, R4RES., 34k, 1/16W, 1% 0402BOURNS, CR0402-FX-3402GLF241R3RES., 169k, 1/16W, 1% 0402, AEC-Q200VISHAY, CRCW0402169KFKED251R13RES., 1MΩ, 1/16W, 1% 0402, AEC-Q200VISHAY, CRCW04021M00FKED261R10RES., 100k, 1/16W, 5% 0402, AEC-Q200VISHAY, CRCW0402100KJNED271R14RES., 2M, 1/16W, 1% 0402, AEC-Q200VISHAY, CRCW04022M00FKED280R17RES., OPTION, 0402291R18RES., 0Ω, 1/10W, 0603, AEC-Q200VISHAY, CRCW06030000Z0EA301VR1TRIMMER 100k 0.25W SMD BOURNS, 3314J-1-104EHardware: For Demo Circuit Only316E1, E2, E10, E11, E13, E15TESTPOINT, TURRET, 0.094" PBF MILL-MAX, 2501-2-00-80-00-00-07-0326E3, E4, E6, E7, E12, E14TESTPOINT, TURRET, 0.061" PBF MILL-MAX, 2308-2-00-80-00-00-07-0332JP1, JP2HEADER 3 PIN 0.079 DOUBLE ROW WURTH ELEKTRONIK, 62000621121341JP3HEADER 2 PIN 0.079 DOUBLE ROW SULLINS CONNECTOR SOLUTIONS, NRPN022PAEN-RC 353XJP1, XJP3, XJP6SHUNT, .079" CENTER WURTH ELEKTRONIK, 608002134216Rev. 07Rev. 0Information furnished by Analog Devices is believed to be accurate and reliable. However , no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.SCHEMATIC DIAGRAM8Rev. 0ANALOG DEVICES, INC. 202112/21ESD CautionESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.Legal Terms and ConditionsBy using the evaluation board discussed herein (together with any tools, components documentation or support materials, the “Evaluation Board”), you are agreeing to be bound by the terms and conditions set forth below (“Agreement”) unless you have purchased the Evaluation Board, in which case the Analog Devices Standard Terms and Conditions of Sale shall govern. Do not use the Evaluation Board until you have read and agreed to the Agreement. Your use of the Evaluation Board shall signify your acceptance of the Agreement. This Agreement is made by and between you (“Customer”) and Analog Devices, Inc. (“ADI”), with its principal place of business at One Technology Way, Norwood, MA 02062, USA. Subject to the terms and conditions of the Agreement, ADI hereby grants to Customer a free, limited, personal, temporary, non-exclusive, non-sublicensable, non-transferable license to use the Evaluation Board FOR EVALUATION PURPOSES ONL Y. Customer understands and agrees that the Evaluation Board is provided for the sole and exclusive purpose referenced above, and agrees not to use the Evaluation Board for any other purpose. Furthermore, the license granted is expressly made subject to the following additional limitations: Customer shall not (i) rent, lease, display, sell, transfer , assign, sublicense, or distribute the Evaluation Board; and (ii) permit any Third Party to access the Evaluation Board. As used herein, the term “Third Party” includes any entity other than ADI, Customer , their employees, affiliates and in-house consultants. The Evaluation Board is NOT sold to Customer; all rights not expressly granted herein, including ownership of the Evaluation Board, are reserved by ADI. CONFIDENTIALITY. This Agreement and the Evaluation Board shall all be considered the confidential and proprietary information of ADI. Customer may not disclose or transfer any portion of the Evaluation Board to any other party for any reason. Upon discontinuation of use of the Evaluation Board or termination of this Agreement, Customer agrees to promptly return the Evaluation Board to ADI. ADDITIONAL RESTRICTIONS. Customer may not disassemble, decompile or reverse engineer chips on the Evaluation Board. Customer shall inform ADI of any occurred damages or any modifications or alterations it makes to the Evaluation Board, including but not limited to soldering or any other activity that affects the material content of the Evaluation Board. Modifications to the Evaluation Board must comply with applicable law, including but not limited to the RoHS Directive. TERMINATION. ADI may terminate this Agreement at any time upon giving written notice to Customer . Customer agrees to return to ADI the Evaluation Board at that time. LIMITATION OF LIABILITY. THE EVALUATION BOARD PROVIDED HEREUNDER IS PROVIDED “AS IS” AND ADI MAKES NO WARRANTIES OR REPRESENTATIONS OF ANY KIND WITH RESPECT TO IT . ADI SPECIFICALL Y DISCLAIMS ANY REPRESENTATIONS, ENDORSEMENTS, GUARANTEES, OR WARRANTIES, EXPRESS OR IMPLIED, RELATED TO THE EVALUATION BOARD INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY, TITLE, FITNESS FOR A PARTICULAR PURPOSE OR NONINFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS. IN NO EVENT WILL ADI AND ITS LICENSORS BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT , OR CONSEQUENTIAL DAMAGES RESUL TING FROM CUSTOMER’S POSSESSION OR USE OF THE EVALUATION BOARD, INCLUDING BUT NOT LIMITED TO LOST PROFITS, DELAY COSTS, LABOR COSTS OR LOSS OF GOODWILL. ADI’S TOTAL LIABILITY FROM ANY AND ALL CAUSES SHALL BE LIMITED TO THE AMOUNT OF ONE HUNDRED US DOLLARS ($100.00). EXPORT . Customer agrees that it will not directly or indirectly export the Evaluation Board to another country, and that it will comply with all applicable United States federal laws and regulations relating to exports. GOVERNING LAW . This Agreement shall be governed by and construed in accordance with the substantive laws of the Commonwealth of Massachusetts (excluding conflict of law rules). Any legal action regarding this Agreement will be heard in the state or federal courts having jurisdiction in Suffolk County, Massachusetts, and Customer hereby submits to the personal jurisdiction and venue of such courts. The United Nations Convention on Contracts for the International Sale of Goods shall not apply to this Agreement and is expressly disclaimed.。

凌特4通道恒定电流LED驱动器
2006 年8 月14 日－北京－凌特公司（Linear Technology Corporation）推出用作4 通道恒定电流LED 驱动器的2MHz DC/DC 转换器LT3476。

该器件每个通道都能驱动多达8 个串联的1A LED，从而使LT3476 能够驱动多达32 个1A LED，同时具有高达96% 的效率。

4 个通道中的每一个都由独立的真正彩色PWM 信号控制，从而对每个通道都能以高达1000:1 的调光比独立调光。

固定频率、电流模式架构确保在宽电源电压和输出电压范围内稳定工作。

频率调节引脚使用户能够在200kHz 至2MHz 的范围内对频率编程，以优化效率，同时最大限度地减小外部器件的尺寸。

其耐热增强型5mm x 7mm QFN 封装有助于为100W LED 应用组成占板面积高度紧凑的解决方案。

LT3476 在LED 高端检测输出电流，从而能够实现降压、降压-升压或升压配置。

用户用一个外部检测电阻对每个通道的输出电流范围编程。

4 个独立驱动器通道中的每一个都使用内部1.5A、36V NPN 开关。

其它特点包括LED 开路保护和热限制。

采用耐热增强型38 引线5mm x 7mm DFN 封装的LT3476EUHF 有现货供应。

以1,000 片为单位批量购买，每片起价为4.64 美元。

概述该LM3478是一种多用途的低边N沟道MOSFET 控制器的开关稳压器。

它是在适当的使用拓扑结构要求，如低边MOSFET，boost，fly-back ，SEPIC 等，此外，LM347可以工作在极高的开关频率，以减少整体解决方案尺寸。

该LM3478开关频率可以调节在100kHz至1MHz的任何值使用一个外部电阻。

电流模式控制亲志愿组织高带宽和瞬态响应，除了逐周期电流限制。

输出电流可以亲编程用一个外部电阻。

已建成的LM3478，如热关断功能，短路保护，过电压保护，电源等。

节能关断模式可将总电源电流5μA，并允许电源排序。

内部软启动限制启动时的浪涌电流。

特点■LM3478Q是AEC - Q100标准认证和生产上的汽车级流■8引脚小型SO8（MSOP- 8）封装■内部推挽驱动1A的峰值电流能力■电流限制和热关断频率补偿电容器和优化，■一个电阻■内部软启动■电流模式操作■滞后欠压闭锁应用■分布式电源系统■电池充电器■离线电源■电信电源■汽车动力系统主要技术指标■宽电源电压范围2.97V至40V■100kHz至1MHz的时钟频率可调■±2.5％（过热）内部参考■10μA关断电流（超温）引脚名称引脚数说明I SEN 1 电流检测输入引脚。

在外部产生的电压电阻输入这个引脚。

COMP 2 补偿引脚。

一个电阻，电容的组合连接到本引脚为控制环路补偿。

FB 3 反馈引脚。

输出电压应调整使用一个电阻分压器提供该脚1.26V。

AGND 4 模拟接地引脚PGND 5 电源地引脚DR 6 驱动引脚。

外部MOSFET的栅极应连接到这个引脚。

FA/SD 7 频率调整和关机引脚。

连接到该管脚的电阻设定振荡器的频率。

该管脚的高层次的时间超过30微秒将关闭设备。

该装置将绘制小于10μA从供给V IN8 电源输入引脚典型的高效率升压型（升压）转换器。

电流模式固定频率升压型DC DC转换器电流模式固定频率升压型dcdc转换器电流模式固定频率升压型dc&sol;dc转换器凌特公司（lineartechnology）面世具备内部3a、42v控制器的电流模式紧固频率降压型dc/dc转换器lt3479。

它在2.5v至24v输出电压范围内工作，适用于于输出电源范围在单节锂离子电池至20v墙上适配器之间的应用领域。

用户可选择使用误差放大器的两个输出，并容许用做降压转换器或负输入。

其42v控制器可以并使输入高达+40v，并可以驱动两个由单节锂离子电池供电和电流高达700ma电流的大电流白光led（串联）。

此外，其控制器频率可以通过300khz至3.5mhz的单个电阻编程，并使设计人员能将外部组件所占到的空间最小化，并躲避系统"噪声关键"频段。

微小/扁平的电感器和陶瓷电容器并使解决方案的占板面积非常紧凑型，而成本也能够最小化。

lt3479的低vcesat开关（0.3v/2.5a）可提供高达89%的效率。

该器件具有可编程软启动功能，以限制启动期间电感器电流，并提供浪涌电流保护，以在短路和电压瞬态变化期间保护lt3479。

扁平（0.75mm）的14引脚4mm×3mmdfn-14封装在小占板面积上具有极好的热性能。

lt3479还采用耐热增强型16引脚tssop封装。

使用4mm×3mmdfn-14PCB的lt3479ede及使用tssop-16ePCB性能概要：lt3479"阔输出电压范围：2.5v至24v"3a、42v内部开关"高效率电源切换：高达89%"集成的软启动"频率由外部电阻设置：200khz至3.5mhz"保护器件免受输入短路及热插拔影响"高vcesat控制器：2.5a时为0.3v（典型值）"提供正和负输出"使用耐磨增强型14引线（4mm×3mm）dfn-14和16引线tssopPCB。