DC1124A QUICK START GUIDE LT3591 LED Driver with Integrated Schottky in 3mm×2mm DFN DESCRIPTION Demonstration circuit 1124 is an LED Driver w ith Integrated Schottky in 3mmx2mm DFN featuring the LT3591. The LT3591 is a fixed frequency step-up current mode DC/DC converter to drive up to ten w hite LEDs in series. The high sw itching frequency allow s using tiny components for the circuit. External components are minimized by integrating the schottky diode and the open circuit protection into the package. The high side current sensing feature of the LT3591 allow s “one w ire” current source, i.e. the low side of the LED string can return to ground anyw here. The input voltage range of the demo board is from 3V to 9V. This driver can provide 20mA for up to 10 LEDs. Different dimming controls can be implemented on the demo board. Please refer to the quick start procedure. The LT3591 datasheet gives complete description of the part, operation and application information. The datasheet must be read in conjunction w ith this quick start guide for w orking on or modifying the demo circuit 1124. Design files for this circuit board are available. Call the LTC factory. ,LTC and LT are registered trademarks ofLinear Technology Corporation. ThinSOT and Pow erPath are trademarks ofLinear Technology Corporation. PERFORMANCE SUMMARY Specifications are at TA = 25°C SYM BO L VIN IOUT PAR AM ETER Input Supply Range ** Output Current η VOPEN IQ IQSHDN Fs Efficiency CAP pin Over voltage Protection Quiescent Current Quiescent Current W hile in Shutdow n Sw itching Frequency CO NDITION S M IN 3 TYP VIN = 3V, 10 LEDs VIN = 3.6V, 10 LEDs LED Open VIN = 3V,VCTR L=3V VIN = 3V,VCTR L=0V 40 78.2 42 0.75 1 M AX 9 20 UN ITS V mA 44 5 11 1.2 % V mA µA M Hz ** The Input Supply R ange of the demo circuit 1124 is limited by the input capacitors. The input voltage absolute maximum rating ofthe LT3591 is 12V. QUICK START PROCEDURE Demonstration circuit 1124 is easy to set up to evaluate the performance of the LT3591. R efer to Figure 1 for proper measurement equipment setup and follow the procedure below : 1 LT3591 NOTE. W hen measuring the input or output voltage ripple,care must be taken to avoid a long ground lead on the oscilloscope probe. M easure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. Place jumper JP1 in the ON position. 1. W ith pow er off,connect the input pow er supply to VIN and G N D. 2. Turn on the pow er at the input. NOTE. M ake sure that the input voltage does not exceed 9V. 3. 4. O nce proper operation is established, adjust the input w ithin the operating range and observe the parameters ofinterest. 5. To test the filtered PW M dimming or the direct DC dimming,apply the PW M or the DC signal to the CTR L terminal and observe the brightness of the LED output. 6. To test the direct PW M dimming, remove C4 and R3. Install Q1 and connect CTR L w ith PW M pin. Apply the PW M signal to the PW M pin and observe the brightness ofthe LED output. Check for the proper voltage and current. NOTE. Ifthe LEDs do not light up,check the jumper setting and LED connection. Figure 1. Proper M easurem ent Equipm ent Setup GND VIN Figure 2. M easuring Input or Output Ripple 2 LT3591 3