ADI LT3950驱动器方案

ADI LT3950 60V 1．5A LED驱动器解决方案

ADI公司的LT3950是60V 1.5A 多拓扑DC/DC转换器,特别设计用来驱动大电流LED.它包含一个1.5A 60V DMOS开关,支持外部PWM调光PMOS.LT3950具有用来调光的内部PWM发生器,把模拟控制信号转变指数标度,用来定义PWM调光占空比.采用指数标度来定义占空比保留了大范围LED电流的调光分辨率.除了恒流源工作模式,LT3950还提供输出电压调整,这可防止LED开路时所带来的危险性.可编程的开关频率在设计高效或降低元件尺寸时提供了灵活性.器件采用扩频调制降低了EMI.开关频率由驱动SYNC/SPRD引脚很容易和外部时钟同步.LED电流通过外接检测电阻进行编程. LT3950工作在升压,SEPIC,降压和降压-升压模式.128:1内部指数标度PWM调光,输入电压从3V到60V,100Hz时20000:1外部PWM调光,±2% LED电流和输出电压调整.主要用在显示器背光,汽车和航空照明.本文介绍了LT3950主要特性,框图和多种应用电路,演示板DC2788A主要指标,电路图, 测试程序建立图.

The LT®3950 is a multitopology DC/DC converter designedspecifically to drive high current LEDs. It contains a 1.5A,60V DMOS switch and supports an external PWM dimmingPMOS. The LT3950 has an internal PWM generatorfor dimming that maps an analog control signal to anexponential scale used to define PWM dimming duty ratio.

Using an exponential scale to define duty ratio preservesdimming resolution across a wide range of LED current.In addition to operating as a constant current source, the LT3950 also provides output voltage regulation. This canbe used to prevent damage to the part in case of open LEDevents. A programmable switching frequency offers flexibility in design for higher efficiency or reduced componentsize. Enabling spread spectrum frequency modulationreduces EMI. The switching frequency can also easilybe synchronized by driving the SYNC/SPRD pin with anexternal clock. LED current is programmed with a singleexternal sense resistor and can be adjusted from zero tofull-scale by an analog signal at the CTRL pin.

LT3950主要特性:

nOperates in Boost, SEPIC, Buck Mode and Buck-Boost Mode n128:1 Internal Exponential Scale PWM Dimming nWide Input Voltage Range (3V to 60V) n1.5A, 60V Internal Switch

n20000:1 External PWM Dimming at 100Hz n±2% LED Current and Output Voltage Regulation nPMOS Switch Driver for PWM Dimming nLED Short/Open Protection and Indication nConstant Voltage and Constant Current Regulation nAdjustable 300kHz to 2MHz Switching Frequency

nAdjustable 100Hz to 1kHz PWM Generator Frequency nInternal Spread Spectrum Frequency Modulation nEasy Synchronization to External Clock nProgrammable VIN UVLO with Hysteresis nAvailable in 16-Lead MSOP Package

LT3950应用: nDisplay Backlighting

nAutomotive and Avionic Lighting

图1.LT3950框图

图2.LT3950典型应用电路图

图3.LT3950 5W降压/升压模式扩频调频LED驱动器

图4.LT39508W升压模式内部10%PWM调光LED驱动器

图5.LT3950 5W SEPIC内部10%PWM调光LED驱动器

图6.LT395036W 降压模式LED驱动器

演示板DC2788A

Demonstration circuit 2788A is a boost LED driver featuring the LT®3950. This demonstration circuit powers a string of LEDs at 330mA. The step-up topology can be used to drive a string of up to 28V of LEDs as assembled. The maximum output voltage capability of the LT3950 is 60V. DC2788A runs from an input voltage range of 6V to 24V as built. It also runs at 2MHz and has the capability to turn on spread spectrum frequency modulation (SSFM) for a frequency range of 2.0MHz to 2.5MHz. Dimming control can be achieved with analog dimming or PWM dimming—either from an external or internally-generated clock source. DC2788A features undervoltage lockout (UVLO) set at 6.6V with a 1.0V hysteresis for turn-on.

The UVLO voltage, LED current, output voltage range, switching frequency, brightness control, SSFM, and the topology can all be adjusted with simple modifications to the demonstration circuit.

LT3950 is a monolithic 1.5A peak switch current, 60V LED driver. The guaranteed peak switch current rating of the IC is 1.5A and this is important to know when calculating maximum output current at a given LED voltage and input voltage for a boost converter. The LT3950 features SSFM and a well-controlled SW node for low emissions.

A frequency range of 200kHz to 2MHz and a high-side PWMTG PWM-dimming MOSFET makes this a very versatile IC for many applications. It can be used for boost, buck-boost mode and buck mode LED driver applications. The PWMTG MOSFET not only provides high PWM dimming ratio capability, but it also serves as a short-circuit protection device. The FAULT flag indicates when there is either a short-circuit or open-LED fault at the output.

The demo circuit is designed to be easily reconfigured to suit other applications, including the example schematics in the data sheet. Consult technical support for assistance.

High voltage operation, 3V input voltage operation, multiple topologies, small-and-compact size, fault protection, low EMI, and multiple brightness control options make the LT3950 flexible and powerful for compact, noise-sensitive LED driver solutions. The LT3950JMSE featured on this demo circuit is available in a thermally enhanced 16-lead plastic MSOP package. The LT3950 data sheet must be read in conjunction with this demo manual to properly use or modify demo circuit DC2788A.

演示板DC2788A主要指标(TA = 25C):

图7.演示板DC2788A外形图

图8.演示板DC2788A测试程序建立图

图9.演示板DC2788A电路图