QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915 WLED DRIVER & LCD BIAS LT3466EDD-1 DESCRIPTION Demonstration circuit DC915 features LT3466-1 high efficiency white LED driver and step-up converter. There is one LED driver output for 8 WLEDs and 2 normal outputs for LCD. VO1 drives 8 LEDs in series with 15mA LED current and VO2/VO3 can delivery +/- 15V at 10mA current. If the charge-pump circuitry (C4, C5 and D1), which generates VO3, is removed, VO2 can deliver over 35mA of current. The input voltage range is 3V to 14V, which can go as low as 2.7V with slightly reduced output current. Each output channel has a jumper (JP1 or JP2) for enabling the output(s) and a CTRL pin (CTRL1 or CTRL2) for LED brightness (current) control or VO2/VO3 voltage adjustment. Placing the jumpers to “/SD” turns off the WLEDs or VO2/VO3, and jumpers to “EN” enables the selected channel of the LT3466-1. Modulating the voltage at CTRL1 or CTRL2 pin respectively can change the LED current at VO1 or VO2/VO3 voltages. As the volt- age on the CTRL1 pin increases from 0V to 1.6V, the feedback voltage across the LED current programming resistor increases from 0 to 200mV, varying the LED current from 0 to 15mA. Similarly, VO2/VO3 voltages increase with voltage on CNTL2. The “CTRL to FB” curves are show in the datasheet. JP3 can conveniently set 8 WLEDs (JP3 jumper at top position), 6 WLEDs (JP3 jumper at bottom position), or open circuit protection test (no jumper), while FB1 terminal monitors the WLED current (VFB1/R1). The overall solution occupies less than 1.62 cm2 with components on one side of the PCB. Design files for this circuit board are available. Call the LTC factory. ________________________________________________ LT is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C unless otherwise noted) PARAMETER FOR LED DRIVER CONDITION VALUE Minimum Input Voltage 3V Maximum Input Voltage 14V LED Current With R1=13.3 ohms 15mA VO2 15V/10mA VO3 -14.5V/10mA Typical Overall Efficiency 3.6V input 82% Typical Switching Frequency With 63.4KΩ timing resistor 800kHz Typical Shutdown Current 3.6V input, both boost shutdown 27uA Typical OVP at VO1 LED string open 39.5V 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915 WLED DRIVER & LCD BIAS QUICK START PROCEDURE DC915 is easy to set up to evaluate the performance of the LT3466-1. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. With power off, connect the input power supply PS1 to VIN and GND. Make sure JP1 and JP2 are set to “EN” positions and JP3 to “8LEDS” (default). 2. Set the input supply at 3.6V. Turn on the power at the input. 3. Observe all white LEDs light up with uniform brightness. The output voltage should measure about 26.5V, FB1 200mV, VO2 15V, and VO3 -14.5V. 4. Test the shutdown function by placing the jumper JP1 to /SD1. Observe LEDs turn off. 5. The LED brightness is controlled by DC voltage PS2 at CTRL1 terminal. With jumper removed from JP1, observe the LED brightness change with DC voltage applied to CNTRL1 pin. The voltage range recommended for dimming is 200mV ~ 1.6V. See the LT3466-1 data sheet for more information on dimming control. 6. Remove PS1 and place the jumper back on JP1 at “EN1” to enable “OVP Test” of the LED string. When jumper on JP3 is removed, VO1 shows the open circuit protection voltage (about 39.5V). When jumper is placed to bottom terminals, only 6 WLEDs light up. 7. When JP2 is set to /SD2, VO2 goes to slightly less than Vin, and VO3 to 0. When both channels are set to the /SD state, the total shut-down current is about 27uA at Vin=3.6V. It increases slightly with Vin. 8. VO2 and VO3 are controlled the same way as the VFB1 vs. VCNTRL1. Note: LT3466-1 can operate up to 22V (it needs to be 1-2V lower than output voltage for the boost converter to work properly). 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915 WLED DRIVER & LCD BIAS Figure 1. Test Connection Diagram 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915 WLED DRIVER & LCD BIAS 4