原标题：Linear LT3952 60V 4A LED驱动方案

　　Linear公司的LT3952是集成了60V 80mΩ DMOS功率开关的电流模式降压DC/DC转换器,4000:1真色彩PWM调光,10:1模拟调光,输入电压3V-42V,输出电压0-60V,主要用在显示器背光,汽车和航空照明,精密限流电压稳压器.本文介绍了LT3952主要特性,框图和几种应用电路,以及演示板DC2013A主要特性,电路图,材料清单和PCB元件布局图.

　　The LT®3952 is a current mode step-up DC/DC converterwith an internal, 60V, 80mΩ DMOS power switch. TheLT3952 is specifically designed to drive high power LEDsin multiple configurations. It combines input and outputcurrent regulation loops with output voltage regulation tooperate as a flexible current/voltage source.

　　Programmable switching frequency with optional spreadspectrummodulation provides EMI reduction, while stillallowing optimization of the external components forefficiency or component size. The LED current is programmablewith an external sense resistor, and can be adjustedfrom zero to full scale with a voltage at the CTRL pin. Theexternal PWM input provides LED ON/OFF control and4000:1 dimming ratio, and an internal PWM generatordelivers the efficiency of PWM dimming to standaloneor I/O limited applications. The LT3952 is available in thethermally enhanced 28-lead TSSOP package.

　　LT3952主要特性:

　　4000:1 True Color PWM™ Dimming

　　4A, 60V Internal DMOS Switch

　　Wide Input Voltage Range: 3V to 42V

　　0V to 60V Output Current Regulation with Monitor

　　PMOS Switch Driver for PWM and Output Disconnect

　　LED Short-Circuit Protection and SHORTLED Flag

　　Internal Spread Spectrum Frequency Modulation

　　Constant-Current and Constant-Voltage Regulation

　　Input Current Limit and Monitor

　　Adjustable Frequency: 200kHz to 3MHz,Synchronizable to an External Clock

　　10:1 Analog Dimming

　　Programmable Open-LED Protection withOPENLED Flag

　　Programmable VIN Undervoltage andOvervoltage Lockout

　　Available in a 28-Lead TSSOP Package

　　LT3952应用:

　　Display Backlighting

　　Automotive and Avionic Lighting

　　Accurate Current-Limited Voltage Regulators

　　图1.LT3952框图

　　图2.LT3952应用电路:广谱频率调制升压LED驱动器

　　图3.LT3952应用电路:输入限流的SEPIC LED驱动器

　　图4.LT3952应用电路:4000:1 PWM调光和过压保护2MHz升压LED驱动器

　　图5.LT3952应用电路:内部PWM调光和缓起动,3MHz降压-升LED驱动器

　　LT3952演示板DC2013A

　　Demonstration Circuit DC2013A is a 60V LED driver with internal 4A switch featuring the LT®3952 monolithic LED driver. It accepts an input voltage from 5V to 36V (with transient to 42V) and boosts to a single string of LEDs up to 50V LEDs at 330mA. DC2013A features an integrated 4A switch, constant-current and constant-voltage output control as well as input current limit and monitoring.

　　The LT3952 has a wide input voltage range down to 3V and up to 42V. It has adjustable switching frequency between 200kHz and 3MHz. It has an option for external frequency synchronization or spread spectrum frequency modulation. It has high PWM dimming capability from an external signal and can be PWM dimmed with an internally generated PWM oscillator and analog input signal. It can be analog dimmed with a control voltage on its control pin. LT3952 features both Open-LED and Short-LED (LED+ to GND) protection as well as fault output flags for each. Although DC2013A is assembled as a boost LED driver, it can be altered to be run as a buck mode, buck-boost mode or boost-buck LED driver.

　　There is another demonstration circuit featuring LT3952 at 2.0MHz (DC2361A). DC2013A features an option to turn on spread spectrum by simply changing the position of a jumper from NO SPREAD to SPREAD or to EXTERNAL SYNC.

　　Small ceramic input and output capacitors are used to save space and cost. The Open-LED overvoltage protection uses the IC’s constant-voltage regulation loop to regulate the output to approximately 55V if the LED string is openedalthough it may reach 59V peak during transient from running LEDs to open. There is a protection diode from LED+ to GND to prevent negative ringing during a short-circuit with long wires.

　　There is undervoltage and overvoltage lockout that can be adjusted on the circuit with a few simple resistor choices.

　　There is an EMI filter on the input of DC2013A. This EMI filter has both an LC stage to reduce EMI below 20MHz and a ferrite bead to reduce higher frequency EMI. The PCB layout contains a small hot-loop for minimized high frequency EMI. The EMI filter can be used by connecting to the “EMI VIN” terminal. However, if the EMI filter is not needed, the input connection can be directly to the PVIN terminal. If the EMI filter is not used, it is recommended to remove the EMI filter if EMI measurements are being made from the PVIN terminal for base EMI testing. It can be replaced for EMI testing at the EMI VIN terminal.

　　The LT3952 data sheet gives a complete description of the part, operation and applications information. The data sheet must be read in conjunction with this Demo Manual for Demonstration Circuit 2013A. The LT3952EFE is as­sembled in a 28-lead plastic TSSOP (FE) package with a thermally enhanced ground pad. Proper board layout is essential for maximum thermal performance. See the data sheet section “Layout Considerations”.

　　LT3952演示板DC2013A材料清单: