LT1937 Datasheet | Linear Technology

LT1937 White LED Step-Up Converter in SC70 and Thin SOT Features s s s s s s s s s DESCRIPTIO Inherently Matched LED Current High Efficiency: 84% Typical Drives Up to Four LEDs from a 3.2V Supply Drives Up to Six LEDs from a 5V Supply 36V Rugged Bipolar Switch Fast 1.2MHz Switching Frequency Uses Tiny 1mm Tall Inductors Requires Only 0.22µF Output Capacitor Low Profile SC70 and Thin SOTTM Packaging U APPLICATIO S s s s s s The LT ®1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three or four LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The LT1937 switches at 1.2MHz, allowing the use of tiny external ponents. The output capacitor can be as small as 0.22µF, saving space and cost versus alternative solutions. A low 95m V feedback voltage minimizes power loss in the current setting resistor for better efficiency. The LT1937 is available in low profile SC70 and Thin SOT packages. , LTC and LT are registered trademarks of Linear Technology Corporation. Thin SOT is a trademark of Linear Technology Corporation. Cellular Phones PDAs, Handheld puters Digital Cameras MP3 Players GPS Receivers TYPICAL APPLICATIO L1 22µH C1 1µF VIN LT1937 OFF ON SHDN GND FB SW Conversion Efficiency D1 C2 0.22µF 15m A EFFICIENCY (%) 90 85 80 VIN = 3V 75 70 65 60 0 5 10 15 LED CURRENT (m A) 20 1937 TA01b VIN 3V TO 5V LED 1 LED 2 LED 3 R1 6.34Ω 1937 F01a C1, C2: X5R OR X7R DIELECTRIC D1: CENTRAL SEMICONDUCTOR CMDSH-3 L1: MURATA LQH3C-220 OR EQUIVALENT Figure 1. Li-Ion Powered Driver for Three White LEDs VIN = 3.6V 1937f ABSOLUTE AXI U RATI GS Input Voltage (VIN) ................................................. SW Voltage ............................................................. FB Voltage .................................................................