LT1937 White LED Step-Up Converter in SC70 and ThinSOT FEATURES DESCRIPTIO n The LT 1937 is a step-up DC/DC converter specifically Inherently Matched LED Current n designed to drive white LEDs with a constant current. The High Efficiency: 84% Typical n device can drive two, three or four LEDs in series from a Drives Up to Four LEDs from a 3.2V Supply n Li-Ion cell. Series connection of the LEDs provides iden- Drives Up to Six LEDs from a 5V Supply n tical LED currents resulting in uniform brightness and 36V Rugged Bipolar Switch n eliminating the need for ballast resistors. The LT1937 Fast 1.2MHz Switching Frequency n switches at 1.2MHz, allowing the use of tiny external Uses Tiny 1mm Tall Inductors n components. The output capacitor can be as small as Requires Only 0.22F Output Capacitor TM n 0.22F, saving space and cost versus alternative solu- Low Profile SC70 and ThinSOT Packaging tions. A low 95mV feedback voltage minimizes power loss U in the current setting resistor for better efficiency. APPLICATIO S The LT1937 is available in low profile SC70 and ThinSOT n Cellular Phones packages. n PDAs, Handheld Computers , LTC and LT are registered trademarks of Linear Technology Corporation. n ThinSOT is a trademark of Linear Technology Corporation. Digital Cameras n MP3 Players n GPS Receivers TYPICAL APPLICATIO Conversion Efficiency L1 90 D1 22H V IN 3V TO 5V 85 C1 C2 LED 1 1F 0.22F 80 V SW IN LED 2 15mA V = 3V IN V = 3.6V IN LT1937 LED 3 75 OFF ON SHDN FB R1 70 GND 6.34 1937 F01a 65 C1, C2: X5R OR X7R DIELECTRIC D1: CENTRAL SEMICONDUCTOR CMDSH-3 L1: MURATA LQH3C-220 OR EQUIVALENT 60 0 510 15 20 LED CURRENT (mA) Figure 1. Li-Ion Powered Driver for Three White LEDs 1937 TA01b 1937f 1 EFFICIENCY (%) U ULT1937 ABSOLUTE AXI U RATI GS (Note 1) Input Voltage (V ) ................................................. 10V Extended Commercial IN SW Voltage ............................................................. 36V Operating Temperature Range (Note 2)... 40C to 85C FB Voltage .............................................................. 10V Maximum Junction Temperature .......................... 125C SHDN Voltage ......................................................... 10V Storage Temperature Range ................. 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C UUW PACKAGE/ORDER I FOR ATIO ORDER PART ORDER PART NUMBER NUMBER TOP VIEW TOP VIEW SW 1 5 V IN LT1937ES5 SW 1 6 V LT1937ESC6 IN GND 2 GND 2 5 GND FB 3 4 SHDN FB 3 4 SHDN S5 PACKAGE S5 PART MARKING SC6 PART MARKING SC6 PACKAGE 5-LEAD PLASTIC TSOT-23 6-LEAD PLASTIC SC70 T = 125C, = 256C/ W IN FREE AIR JMAX JA LTYN T = 125C, = 256C/ W IN FREE AIR LAAB JMAX JA = 120C ON BOARD OVER GROUND PLANE JA = 150C ON BOARD OVER GROUND PLANE JA Consult LTC Marketing for parts specified with wider operating temperature ranges. T = 25C, V = 3V, V = 3V, unless otherwise noted. ELECTRICAL CHARACTERISTICS A IN SHDN PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Operating Voltage 2.5 V Maximum Operating Voltage 10 V Feedback Voltage I = 100mA, Duty Cycle = 66% 86 95 104 mV SW FB Pin Bias Current 10 45 100 nA Supply Current 1.9 2.5 mA SHDN = 0V 0.1 1.0 A Switching Frequency 0.8 1.2 1.6 MHz Maximum Duty Cycle 85 90 % Switch Current Limit 320 mA Switch V I = 250mA 350 mV CESAT SW Switch Leakage Current V = 5V 0.01 5 A SW SHDN Voltage High 1.5 V SHDN Voltage Low 0.4 V SHDN Pin Bias Current 65 A Note 1: Absolute Maximum Ratings are those values beyond which the life Note 2: The LT1937E is guaranteed to meet specifications from 0C to of the device may be impaired. 70C. Specifications over the 40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. 1937f 2 U WWW