Linear公司的LTR3756, LT3756-1和LT3756-2 是驱动大电流LED的DC/DC控制器,输入电压力V-100V,输出电压高达100V,PWM调3000:1,恒流和恒压稳压,可调频率100kHz到1MHz,能以升压,降压,升-降模式,SEPIC或反激拓扑驱动LED,主要用于大功率LED应用,限流恒压应用和电池充电.本文介绍了LT3756主要特性,方框图,多种LED驱动应用电路,以及评估板1319B-A/1319B-B主要特性,电路图和材料清单.
The LTR3756, LT3756-1 and LT3756-2 are DC/DC controllers designed to operate as a constant-current source for driving high current LEDs. They drive a low side external N-channel power MOSFET 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 LT3756/LT3756-1/LT3756-2 sense 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.

LT3756主要特性:
3000:1 True Color PWM™ Dimming
Wide Input Voltage Range: 6V to 100V
Output Voltage Up to 100V
Constant-Current and Constant-Voltage Regulation
100mV 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
Improved Open LED Status Pin (LT3756-2)
Frequency Synchronization (LT3756-1)
PWM Disconnect Switch Driver
CTRL Pin Provides Analog Dimming
Low Shutdown Current: <1μA
Programmable Soft-Start
Thermally Enhanced 16-Lead QFN (3mm × 3mm) and MSOP Packages

LT3756应用:
High Power LED Applications
Current Limited Constant Voltage Applications
Battery Charging

图1.LT3756方框图


图2.LT3756 30W汽车头灯驱动电路图

图3.LT3756降压-升压模式LED驱动器

图4.LT3756效率90% 20W SEPIC LED驱动电路

图5.LT3756效率94% 30W白光LED头灯驱动电路

图6.LT3756 125W 83V/1.5A效率97运动场照明LED驱动电路

图7.LT3756  80Vin降压模式PWM调光单个或两个LED驱动电路

图8.LT3756宽电压Vin和VLED的降压升压模式LED驱动电路

评估板1319B-A/1319B-B
Demonstration circuit 1319B-A/1319B-B is a high voltage and high current LED driver controller. The VIN pin input voltage is as high as 100V, and the LED output voltage is also as high as 100V. The demonstration circuit is assembled as a boost topology from 8V to 80V input and up to 80V LED output at 0.5A with an open-LED status pin (DC1319B-A) or a sync input pin (DC1319B-B). DC1319B features PWM dimming, analog dimming, shutdown, and open-LED overvoltage protection. Effi ciency at 12VIN is as high as 91% for 40W output.
The switching frequency is set at 300kHz to accommodate the automotive switching frequency range. Small ceramic input and output capacitors are used to save space and cost and a high voltage 100V external power switch and a 100V catch diode are used for up to 40W (80V at 0.5A) output as assembled. The open-LED overvoltage protection limits the output to approximately 92V if the LED string is opened.
Note: LED output voltages above 80V, but less than the open-LED voltage of 92V, are possible with limitations to low input voltage operation. Please consult the factory.
For low input voltage operation, the CTRL pin voltage is reduced as the input voltage drops below 10V, reducing L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear  Technology Corporation. All other trademarks are the property of their respective owners.
LED brightness and restraining the peak switch currents in order to limit inductor and switch size. UVLO turns the LEDs off when VIN drops below 8V.
DC1319B PWM dimming is simple. The boost topology LED string returns to the LED terminal and the PWM dimming MOSFET turns the LED string on and off with an input to the PWM dimming terminal. For the highest PWM dimming ratio, it is recommended to use 100Hz as a PWM dimming frequency. Information regarding PWM dimming ratios and performance can be found in the LT3756-2/LT3756-1 data sheet in the Applications Information section.
Soft-start is provided with a simple and small capacitor to maintain control of the switch current during turn on for high power designs.
Modifi cations can be made to the DC1319B in order to convert the board from a boost topology LED driver to any other topology. Please consult the factory or LT3756-2/ LT3756-1 data sheet for details regarding how to customize the DC1319B or how to design different topologies for custom specifi cations.

图9.DC1319B-A/DC1319B-B评估板测试框图



图10.DC1319B-A/DC1319B-B评估板电路图

评估板材料清单(BOM):