QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 507 SINGLE CELL WHITE LED DRIVER LT1937 DESCRIPTION Demonstration circuit 507 features the LT1937 constantcurrent white LED driver in a small SC70 package. The demo board consists of two circuits: an efficiency circuit designed to demonstrate high efficiency performance of the LT1937 using the Murata inductor and a size circuit highlighting the LT1937’s ability to work with a small ceramic chip inductor and a small output capacitor (0.22µF). The high efficiency and small circuit size are made possible by a 95mV feedback voltage and 1.2MHz switching frequency, making the LT1937-SC70 an ideal solution for battery powered portable applications such as cellular phones, digital cameras, MP3 players, GPS receivers, and handheld computers (PDAs). The DC507 is specifically designed for white LED backlight applications using 2–4 LEDs in series. LT1937 offers numerous LED-dimming circuit options, see the datasheet for more detailed information on LED brightness control. Design files for this circuit board are available. Call the LTC factory. QUICK START PROCEDURE Demonstration circuit 507 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. 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. When measuring the output ripple, see Figure 2 for proper scope probe technique. TEST THE EFFICIENCY CIRCUIT (UPPER CIRCUIT) 2. Place jumper JP2 in the EFFICIENCY position. 3. Press the SW1 switch. Observe all four white LEDs light up. The output voltage should measure about 13V across the Vout Test terminal to GND terminal. 4. Turn off the input power supply or disconnect the sin- gle cell Li-Ion battery. TEST THE SIZE CIRCUIT (LOWER CIRCUIT) 5. Place jumper JP2 in the SIZE position. SET THE INPUT VOLTAGE SOURCE 1. The demo board can be powered from the 3V Lithium battery installed on the demo board (B1) or other input source (bench top power supply) by selecting input source jumper (JP1). a. For battery (B1) input operation, place the jumper (JP1) in the BATTERY position. b. 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. 6. Turn on the input power supply or connect the single cell Li-Ion battery. 7. Press the SW2 switch. Observe all four white LEDs light up. The output voltage should measure about 13V across the Vout Test terminal to GND terminal. LED BRIGHTNESS CONTROL The brightness of the LEDs can be controlled by applying a PWM signal to the SHDN terminal (use the upper SHDN terminal for the EFFICIENCY circuit and lower SHDN terminal for the SIZE circuit). 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 on PWM dimming control. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 507 SINGLE CELL WHITE LED DRIVER – + + – + + – – Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Scope Probe Placement for Measuring Input or Output Ripple 2 5 4 VIN BATTERY L1 JP2 22uH 3 E1 JP1 3 Vin 2.7V - 5V 3 2 2 D1 Vout Test CMDSH-3 E3 EFFICIENCY SIZE 2 1 LED1 SW1 1 1 D D LED2 ON/OFF 6 Vin B1 BATTERY + C1 2.2uF 6.3V R2 12mA 1 SW LED3 C2 0.47uF 16V U1 LT1937ESC6 LED4 WHITE 4 SHDN 100K FB 3 GND GND 2 5 R1 8.06 1% E5 SHDN GND GND E2 E4 C C D2 L2 22uH CMDSH-3 SW2 ON/OFF C4 2.2uF 6.3V B R3 100K 4 6 1 Vin SW SHDN FB C3 0.47uF 16V U2 LT1937ESC6 3 B GND GND 2 5 E6 SHDN CONTRACT NO. A APPROVALS DRAWN DATE June Wu 2/13/02 DAVE KIM 2/13/02 TECHNOLOGY 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 A TITLE CHECKED LT1937ESC6, SINGLE CELL WHITE LED DRIVER APPROVED ENGINEER SIZE CAGE CODE DESIGNER DWG NO REV DC507A Thursday, March 21, 2002 5 4 3 SCALE: 2 FILENAME: A SHEET 1 1 OF 1 Bill Of Material Demo Bd. #507A Linear Technology Corporation LT1937ESC6 6/17/2005 Item Qty Reference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0 2 1 1 2 2 2 6 2 2 4 1 2 2 2 1 B1 B1 HOLDER L1 L2 C1,C4 C2,C3 D1,D2 E1,E2,E3,E4,E5,E6 JP1,JP2 JP1,JP2 LED1-LED4 R1 R2,R3 SW1,SW2 U1,U2 Part Description BATTERY, AA BATTERY HOLDER, INDUCTOR, 22uH INDUCTOR, 22uH CAP., X5R, 2.2uF, 6.3V, 20% 0603 CAP., X5R, 0.47uF, 16V 20% 0603 DIODE, CMDSH-3, SOD-323 TESTPOINT, TURRET, .094" JUMPER, 0.079, 3 PIN SHUNT, LED, NSCX SERIES, WHITE RES., CHIP, 8.06, 1/16W, 1% 0402 RES., CHIP, 100K, 1/16W, 5% 0402 SWITCH MOMENTARY IC., LT1937ESC6, SC70 PRINTED CIRCUIT BOARD Page 1 - of - 1 Manufacture / Part # SANYO., CR2, KEYSTONE, 92 MURATA, LQH32CN220K51 TAIYO YUDEN, LB2012T220M AVX, 06036D225MAT AVX, 0603YD474MAT Central Semi. CMDSH-3 MILL-MAX, 2501-2 COMM CON, 2802S-03G1 COMM CON. CCIJ2MM-138G NICHIA, NSCW100 AAC., CR05-8R06FM AAC., CR05-104JM PANASONIC EVQ PJS 05K LINEAR., LT1937ESC6 DEMO CIRCUIT 507A