Linear 公司的LT3956 是80V輸入80V輸出恒流恒壓DC/DC轉換器,非常適合用來驅動大電流高亮度LED(HBLED).3000:1真彩色PWM調光,輸入電壓從4.5V到80V,輸出電壓高達80V,內部集成了3.3V/80V開關,可調頻率從100kHz到1MHz,能以升壓,降壓,升降壓,SEPIC或反激模式驅動LED,主要用于大功率LED,電池充電器和精密電流限壓穩壓器.本文介紹了LT3956主要特性,方框圖,以及多種應用電路,包括效率95%25W WLED汽車頭燈驅動電路圖, 升-降壓模式LED驅動電路圖, 超大電容充電電路圖,以及降壓模式90W LED驅動電路圖等.

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應用:

High Power LED

Battery Charger

Accurate Current Limited Voltage Regulator

圖1. LT3956方框圖

圖2. LT3956效率95%25W WLED汽車頭燈驅動電路圖

圖3. LT3956升-降壓模式LED驅動電路圖

圖4. LT3956超大電容充電電路圖

圖5. LT3956效率90% 20W SPEIC LED驅動電路圖

圖6. LT3956降壓模式90W LED驅動電路圖