QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 484 SINGLE CELL WHITE LED DRIVER LT1937 DESCRIPTION white LED backlight applications using 2–4 LEDs, making LT1937-SOT23 an ideal solution for battery powered portable applications such as cellular phones, digital cameras, MP3 players, GPS receivers, and handheld computers (PDAs). LT1937 offers numerous LED dimming circuit options, see the datasheet for details. Demonstration circuit 484 features the LT1937 constantcurrent white LED driver in a small SOT23 ThinSOT package. The demo board is designed to demonstrate the high efficiency performance and the small size of the LT1937. The LT1937 features a 95mV feedback voltage, 1.2MHz switching frequency and a special internal compensation network, which allows small (0603) input and output capacitors. DC484 is specifically designed for Design files for this circuit board are available from the LTC factory. QUICK START PROCEDURE For bench supply input, place the jumper (JP1) in the Vin position and connect a 3.3V, 500mA Bench supply to the Vin and GND terminals. Demonstration circuit 484 is easy to set up to evaluate the performance of the LT1937. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 2. Turn on the input power supply or connect the single cell Li-Ion battery. Turn on the LT1937 LED driver circuit by pushing down SW1. Observe all four white LEDs light up. The output voltage should measure about 13V across the Vout Test terminal to GND terminal. NOTE: When measuring the input or output voltage rip- ple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure 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. 3. The brightness of the LEDs can be controlled by ap- plying a PWM signal to the SHDN terminal. The typical frequency range recommended for PWM dimming is 1KHz–10KHz with the signal magnitude of the PWM signal higher than 1.5V. See the LT1937 data sheet for more information about PWM dimming control. 1. The demo board can be powered from a 3V Lithium battery installed on the demo board (B1) or other input source (bench top power supply) by selecting input source jumper (JP1). For battery (B1) input operation, place the jumper (JP1) to the “BATTERY” position. OPTIONAL SUPPLY TO ON-BOARD BATTERY – + + + – – + OPTIONAL DIMMING CONTROL VIA 1KHz-10KHz PWM SIGNAL (>1.5V) SEE LT1937 DATASHEET FOR DETAILS – GND VIN Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Ripple 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 484 SINGLE CELL WHITE LED DRIVER Vin 2.7V - 5 V 3 E1 JP1 2 VIN BATTERY D1 Vou t Test CMDSH-3 E3 L1 1 22uH LED1 SW1 LED2 ON/OFF 5 1 Vin SW 12mA LED3 U1 LT1937E S5 LED4 B1 BATTERY + C1 1uF 6.3V R2 100K WHITE 4 SHDN FB 3 C2 0. 22uF 16V GND 2 E5 R1 7. 5 1% SHDN GND GND E2 E4 Figure 3. Schematic 2 5 4 3 2 1 Vin 2.7V - 5V D D 3 E1 JP1 2 VIN BATTERY D1 L1 22uH Vout Test E3 1 CMDSH-3 LED1 SW1 LED2 ON/OFF C 5 1 Vin SW 12mA LED3 U1 LT1937ES5 C LED4 B1 BATTERY + C1 1uF 6.3V R2 WHITE 4 SHDN 100K FB 3 C2 0.22uF 16V GND 2 R1 7.5 1% E5 SHDN B B GND GND E2 E4 CONTRACT NO. APPROVALS DRAWN DATE June Wu 11/27/01 TECHNOLOGY TITLE CHECKED LT1937ES5, SINGLE CELL WHITE LED DRIVER APPROVED A ENGINEER 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 David Chen 11/27/01 DESIGNER SIZE CAGE CODE DWG NO REV A DEMO DC484A Friday, December 14, 2001 5 4 3 SCALE: FILENAME: 2 SHEET A 1 OF 1 1 Bill Of Material Demo Bd. #484A Linear Technology Corporation LT1937ES5 6/17/2005 12:34 PM Item Qty Reference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 2 1 1 1 1 5 1 1 4 1 1 1 1 1 B1 B1 HOLDER L1 C1 C2 D1 E1,E2,E3,E4,E5 JP1 JP1 (BATTERY SIDE) LED1-LED4 R1 R2 SW1 U1 Part Description BATTERY, AA BATTERY HOLDER, INDUCTOR, 22uH CAP., X5R, 1.0uF, 6.3V, 20% 0603 CAP., X7R, 0.22uF, 16V 20% 0805 DIODE, CMDSH-3, SOD-323 TESTPOINT, TURRET, .094" JUMPER, 0.079, 3 PIN SHUNT, LED, NSCX SERIES, WHITE RES., CHIP, 7.5, 1/16W, 1% 0402 RES., CHIP, 100K, 1/16W, 5% 0402 SWITCH MOMENTARY IC., LT1937, SOT23-S5 PRINTED CIRCUIT BOARD Page 1 - of - 1 Manufacture / Part # SANYO., CR2 KEYSTONE, 92 MURATA, LQH32CN220K51L TAIYO YUDEN, JMK107BJ105MA TAIYO YUDEN, EMK212BJ224MG Central Semi. CMDSH-3 MILL-MAX, 2501-2 COMM CON, 2802S-03G1 COMM CON. CCIJ2MM-138G NICHIA, NSCW100 AAC., CR05-7R50FM AAC., CR05-104JM PANASONIC EVQ PJS 05K LINEAR., LT1937ES5 (Bulk) DEMO BOARD DC484A