一种LT3956 80V恒流恒压HBLED驱动的设计

 

    凌力尔特公司（Linear）推出80V高压侧电流检测DC/DC转换器LT3956,该器件为作为恒定电流和恒定电压稳压器工作而设计。它非常适用于驱动大电流LED以及给电池和超级电容器充电。其4.5V至80V输入电压范围使其非常适用于多种应用，包括汽车、工业和建筑照明。LT3956使用一个内部N沟道MOSFET,可以从标称值为12V的输入驱动多达18个350mA的白光LED,从而提供超过25W的功率。它采用高压侧电流检测，允许使用升压、降压、降压-升压或SEPIC和反激式拓扑。LT3956在升压模式时提供超过94%的效率，从而无需外部散热措施。一个频率调节引脚允许用户在100kHz至1MHz范围设定频率，从而优化了效率，同时限度地减小外部组件的尺寸和成本。结合5×6mmQFN封装，LT3956提供一个高度紧凑的25WLED驱动器解决方案。

    The LT?3956 is a DC/DC converter designed to operate as a constant-current source and constant-voltage regulator. It is ideally suited for driving high current LEDs. It features an internal low side N-channel power MOSFET rated for 84V at 3.3A and driven from an internal regulated 7.15V supply. The fixed frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages. A ground referenced voltage FB pin serves as the input for several LED protection features, and also makes it possible for the converter to operate as a constant-voltage source. A frequency adjust pin allows the user to program the frequency from 100kHz to 1MHz to optimize efficiency, performance or external component size.

    The LT3956 senses output current at the high side of the LED string. High side current sensing is the most flexible scheme for driving LEDs, allowing boost, buck mode or buck-boost mode configuration. The PWM input provides LED dimming ratios of up to 3000:1, and the CTRL input provides additional analog dimming capability.

    LT3956主要特性：

    3000:1TrueColorPWM调光

    宽输入电压范围：4.5V至80V

    输出电压高达80V

    内部3.3A/84V开关

    恒定电流和恒定电压调节

    250mV高压侧电流检测

    以升压、降压、降压-升压、SEPIC或反激式拓扑驱动LED

    可调频率：100kHz至1MHz

    LED开路保护

    具迟滞的可编程欠压闭锁

    恒定电压环路状态引脚

    PWM断接开关驱动器

    CTRL引脚调节高压侧电流检测门限

    低停机电流：<1μA

    可编程软启动

    采用36引线（5×6mm）QFN封装

    LT3956应用：

　　高功率LED
　　蓄电池充电器
　　准确的电流限制电压调节器

图1. LT3956方框图

图2. LT3956效率95%25W WLED汽车头灯驱动电路图

图3. LT3956升-降压模式LED驱动电路图

图4. LT3956超大电容充电电路图

图5. LT3956效率90% 20W SPEIC LED驱动电路图

图6. LT3956降压模式90W LED驱动电路图