Linear 公司的LT3956 是80V输入80V输出恒流恒压DC/DC转换器，非常适合用来驱动大电流高亮度LED(HBLED).3000:1真彩色PWM调光，输入电压从4.5V到80V，输出电压高达80V，内部集成了3.3V/80V开关，可调频率从100kHz到1MHz，能以升压，降压，升降压，SEPIC或反激模式驱动LED，主要用于大功率LED，电池充电器和精密电流限压稳压器.本文介绍了LT3956主要特性，方框图，以及多种应用电路，包括效率95%25W WLED汽车头灯驱动电路图， 升-降压模式LED驱动电路图， 超大电容充电电路图，以及降压模式90W LED驱动电路图等.

80VIN， 80VOUT Constant-Current，Constant-Voltage Converter

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:

3000:1 True Color PWMTM Dimming

Wide Input Voltage Range: 4.5V to 80V

Output Voltage Up to 80V

Internal 3.3A/84V Switch

Constant-Current and Constant-Voltage Regulation

250mV High Side Current Sense

Drives LEDs in Boost， Buck Mode， Buck-Boost Mode， SEPIC or Flyback Topology

Adjustable Frequency: 100kHz to 1MHz

Open LED Protection

Programmable Undervoltage Lockout with Hysteresis

Constant-Voltage Loop Status Pin

PWM Disconnect Switch Driver

CTRL Pin Adjusts High Side Current Sense Threshold

Low Shutdown Current: <1μA

Programmable Soft-Start

Available in the 36-Lead (5mm × 6mm) QFN Package

LT3956应用:

High Power LED

Battery Charger

Accurate Current Limited Voltage Regulator

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

详情请见:
http://cds.linear.com/docs/Datasheet/3956f.pdf