DEMO MANUAL DC1160 LT3518: Full-Featured LED Driver with 2.3A Switch Current DESCRIPTION The high side PMOS PWM dimming MOSFET can be Demonstration circuit 1160 is a full-featured LED driver used to achieve 3000:1 PWM dimming ratio. The board with 2.3A switch current featuring the LT 3518. The board is programmed for 1MHz oscillator frequency, but can is optimized to drive a 330mA LED string with a total LED be adjusted by changing R14. Higher frequency results voltage between the input voltage and 40V in a boost to- in higher PWM dimming ratio. pology. The high input voltage range, high ef ciency low side internal 2.3A NPN power switch, low voltage oating The V pin can be tied directly to PV for simplicity or IN IN current sense ampli er, soft-start, high side PMOS PWM powered from an additional low voltage input such as gate driver, high PWM dimming ratio, overvoltage protec- 3.3V for higher ef ciency operation and lower on-chip tion, shutdown control pin, analog LED current dimming power dissipation. control, and externally programmable switching frequency A few simple modi cations can be made to DC1160 in (with sync) make the LT3518 an extremely versatile and order to convert the board from a boost LED driver to a powerful LED driving IC. buck mode or buck-boost mode LED driver. Please consult The LT3518 has a 45V switch with 2.3A peak switch cur- the data sheet for schematic details and the factory for rent limit rating. DC1160 has overvoltage protection at customization details. 40V if the LEDs are open or not properly attached to the The LT3518 data sheet gives a complete description of the terminals on the PCB. The shutdown function is activated part, operation and applications information. The data sheet by pulling the shutdown terminal to ground. In shutdown must be read in conjunction with this Quick Start Guide for the boost con guration allows the input voltage to be seen demonstration circuit 1160. The LT3518 is assembled in a on the output and if the attached LED array leaks current small 16-lead plastic (4mm 4mm) QFN UF package with at the input voltage, the LEDs may not completely turn off. a thermally enhanced ground pad. Proper board layout is If the top gate is installed, it will provide shutdown output essential for maximum thermal performance. See the data disconnect and the LEDs will turn off during shutdown. sheet section Layout Considerations. The CTRL terminal can be used to analog dim the LED current. In order to use the CTRL terminal, R6 (0) pull- Design les for this circuit board are available at up short resistor must be removed and replaced with a DEMO MANUAL DC1160 QUICK START PROCEDURE DC1160 is easy to set up to evaluate the performance of 5. Turn PV power on. IN the LT3518. Follow the procedure below: 6. Turn V power on and observe the regulated LED cur- IN Note: Make sure that the PV input voltage does not exceed rent, the circuit ef ciency, etc. without looking directly IN 40V and that the V input voltage does not exceed 30V. at the LEDs. IN 1. Connect a string of LEDs with forward voltage less than 7. For PWM dimming, tie a 100Hz, 3V to 5V PWM waveform + 40V, but greater than the PV input voltage, to the LED to the PWM terminal and GND and observe the PWM IN and GND terminals on the PCB as shown. dimming LED current and PWM gate waveforms. 2. With power off, connect a 3.3V input power supply to 8. For shutdown, tie the SHDN terminal to GND and the V and GND terminals on the PCB. observe the LED current dropping to zero and the V IN IN input current dropping to about 65mA with R4 installed 3. With power off, connect a 3V to 40V input power supply (V /51k). IN to PV and GND terminals on the PCB. PV should IN IN not exceed the attached LED string voltage. PWM 4. Connect a 3.3V source to PWM and GND. 5V/DIV I LED 200mA/DIV 100 90 I L1 1A/DIV 80 70 DC1160 F02 1s/DIV 60 Figure 2. 3000:1 PWM Dimming at 100Hz, 50 PV = 12V, V = 30V IN LED 40 30 V = 12V IN CTRL = V REF 20 0 20 40 60 80 100 PWM DUTY CYCLE (%) DC1160 F01 Figure 1. DC1160A Ef ciency 30V LED String, PV = V = 12V IN IN dc1160f 2 EFFICIENCY (%)