DEMO CIRCUIT 1612A-A/B HIGH FREQUENCY SEPIC LED DRIVER LT3519-1/LT3519-2 DESCRIPTION Demonstration Circuit 1612A is a fully integrated LED driver with 750mA switch current featuring the LT®3519-1/LT3519-2. The board is optimized to drive an LED string of up to 16V at 150mA in a SEPIC topology. The high input voltage range, highefficiency low-side integrated 45V 750mA power switch and catch diode, integrated compensation, low voltage floating current sense amplifier, high pwm dimming ratio, overvoltage protection, shutdown control pin, analog LED current dimming control, and fixed 1MHz/2.2MHz switching frequency make the LT3519-1/LT3519-2 an extremely versatile and powerful high frequency LED driving IC. DC1612A has overvoltage protection at 18V in case the LEDs are open or not properly attached to the terminals on the PCB. The shutdown function is activated by pulling the SHDN/UVLO terminal to ground. The CTRL terminal can be used to analog dim the LED current. The CTRL terminal is pulled up with a resistor divider between PVIN and GND. As PVIN drops below 7.4V, CTRL voltage drops below its fullscale threshold and the LED current scales back. The VIN pin is tied directly to the PVIN terminal through R8, a zero ohm resistor. The VIN pin and terminal can be separated from PVIN for some applications such as buck mode by removing R8. A few simple modifications can be made to DC1612A in order to convert the board from a SEPIC LED driver to a boost, buck mode, or buck-boost mode LED driver. Please consult the datasheet for schematic details and the factory for customization details. The LT3519/-1/-2 datasheet gives a complete description of the part, operation and applications information. The datasheet must be read in conjunction with this Quick Start Guide for Demonstration Circuit 1612A. The LT3519-1/-2 is assembled in a small 16lead plastic MSOP package. Proper board layout is essential for maximum thermal performance. See the datasheet section ‘Layout Considerations’. Design files for this circuit board are available. Call the LTC factory. L and LT are registered trademarks of Linear Technology Corporation. Table 1. Typical Performance Summary for DC1612A-A LT3519-1 PARAMETER FOR DC1612A-A LT3519-1 CONDITION VALUE (TYPICAL) PVIN=VIN Input Voltage Range Operating 6V-24V PVIN=VIN Full-Scale LED Current Input Voltage Range ILED=150mA R6=1MΩ R7=174kΩ 8V-24V Switching Frequency LT3519-1 1MHz LED String Current ILED R1=1.69Ω 150mA OVP Open LED Voltage R2=1MΩ R3=69.8kΩ 18V Efficiency PVIN=VIN=12V VLED=16V ILED=150mA 80.8% Under Voltage Lockout Low Voltage Rising Turn-On (UVLO + VHYST) R4=1MΩ R5=261kΩ 6.0V 8.1V 1 DEMO CIRCUIT 1612A-A/B HIGH FREQUENCY SEPIC LED DRIVER Table 2. Typical Performance Summary for DC1612A-B LT3519-2 PARAMETER FOR DC1612A-B LT3519-2 CONDITION VALUE (TYPICAL) PVIN=VIN Input Voltage Range Operating 7V-24V PVIN=VIN Full-Scale LED Current Input Voltage Range ILED=150mA R6=1MΩ R7=174kΩ 8V-24V Switching Frequency LT3519-2 2.2MHz LED String Current ILED R1=1.69Ω 150mA OVP Open LED Voltage R2=1MΩ R3=69.8kΩ 18V Efficiency PVIN=VIN=12V VLED=16V ILED=150mA 79.4% Under Voltage Lockout 7.0V R4=1MΩ R5=215kΩ Low Voltage Rising Turn-On (UVLO + VHYST) 9.1V QUICK START PROCEDURE DC1612A is easy to set up to evaluate the performance of the LT3519-1/LT3519-2. Follow the procedure below: sure that the input voltage does not exceed 24V at all times. 1. 2. Connect a string of LEDs with forward voltage less than 16V (at 150mA) to the LED+ and LEDterminals on the PCB as shown. With power off, connect a 6V*-24V input power supply to the VIN (or PVIN) and GND terminals on the PCB. EFFICIENCY NOTE: Make 100% 16V LED string 90% LT3519-1 80% LT3519-2 70% 60% 5 10 15 20 25 INPUT VOLTAGE (V) Figure 1. DC1612A Efficiency vs. PVIN 16VLED 150mA NOTE: *6V is the minimum input voltage for DC1612A-A. 7V is the minimum input voltage for DC1612A-B. 24V is the maximum input voltage for both SEPIC applications with 16V LED and 18V OVP. 3. Connect a 5V source to PWM and GND. 4. Turn the input power on and observe the regulated LED current, the circuit efficiency, etc. without looking directly at the LEDs. 5. For PWM dimming, tie a 100Hz (or higher), 5V PWM waveform to the PWM terminal and GND and observe the PWM dimming LED current and PWM gate waveforms. 6. Figure 2. DC1612A-A 16VLED PWM Dimming PVIN=12V For shutdown, tie the SHDN/UVLO terminal to GND and observe the IC turning off. 2 DEMO CIRCUIT 1612A-A/B HIGH FREQUENCY SEPIC LED DRIVER Figure 3. DC1612A-B 16VLED PWM Dimming PVIN=12V Figure 4. Proper Measurement Equipment Setup 3 DEMO CIRCUIT 1612A-A/B HIGH FREQUENCY SEPIC LED DRIVER TERMINAL OPTIONS OPENLED – The OPENLED terminal is tied directly to the OPENLED pin. If there is a open LED condition, the terminal is pulled low. When there is no fault, the terminal is pulled up to VIN with a 100k resistor. This terminal can be monitored with a voltage meter, tied to the input of another device, or left floating. SHDN/UVLO – This terminal is tied directly to the SHDN/UVLO pin. A resistor divider from PVIN to GND sets the voltage on this terminal/pin. These resistors can be easily adjusted for both the UVLO level and the amount of rising hysteresis. See the datasheet for details. The terminal can also be used to shut the IC down and turn off the LEDs. Tie the terminal directly to GND or place a voltage on the terminal below the shutdown threshold of the IC in order to place the IC in shutdown and turn off the LEDs. CTRL – This terminal is tied directly to the CTRL pin. A resistor divider from PVIN to GND sets the voltage on this terminal/pin. PVIN below 8V reduces the LED current (analog dimming) below 150mA. The divider can be adjusted for different analog dimming levels. Pulling the CTRL pin to GND turns the LEDs off. An exter- nal voltage applied to the CTRL terminal can reduce the LED current. See the datasheet for analog dimming details. It is okay to float this terminal. PWM – This terminal is tied directly to the PWM pin and to the gate of the N-Channel MOSFET in series with the LED string. M1 requires a 5V gate drive for proper operation, but a lower voltage MOSFET can be used in its place. PWM dimming performance of the LT3519-1/-2 is discussed in the datasheet. Make sure to supply a proper PWM dimming voltage, frequency, and duty cycle to the LT3519-1/-2 SEPIC application. If PWM dimming is not used, the PWM terminal can be tied directly to a 5V DC source. If this terminal is left unconnected, the LEDs will not turn on. VIN and PVIN – VIN is tied directly to the VIN pin of the IC. PVIN is tied directly to the inductor. The two are shorted together with a zero ohm resistor R8. R8 can be removed and VIN can be powered separately from PVIN or VIN can be tied directly to the OUT terminal for buck mode operation with resistor option R14. 4 DEMO CIRCUIT 1612A-A/B HIGH FREQUENCY SEPIC LED DRIVER 5