LT3474/LT3474-1 Step-Down 1A LED Driver FEATURES DESCRIPTION n True Color PWM Delivers Constant Color with The LT 3474/LT3474-1 are xed frequency step-down 400:1 Dimming Range DC/DC converters designed to operate as constant-current n sources. An internal sense resistor monitors the output Wide Input Range: 4V to 36V n current allowing accurate current regulation, ideal for Up to 1A LED Current n driving high current LEDs. High output current accuracy Adjustable 200kHz2MHz Switching Frequency n is maintained over a wide current range, from 35mA to Adjustable Control of LED Current n 1A, allowing a wide dimming range. Integrated Boost Diode n High Output Current Accuracy is Maintained Unique PWM circuitry allows a dimming range of 400:1, Over a Wide Range from 35mA to 1A avoiding the color shift normally associated with LED n Open LED (LT3474) and Short-Circuit Protection current dimming. n High Side Sense Allows Grounded The high switching frequency offers several advantages, Cathode Connection permitting the use of small inductors and ceramic capaci- n Uses Small Inductors and Ceramic Capacitors tors. Small inductors combined with the 16-lead TSSOP n LT3474-1 Drives LED Strings Up to 26V surface mount package save space and cost versus n Compact 16-Lead TSSOP Thermally Enhanced alternative solutions. The constant switching frequency Surface Mount Package combined with low-impedance ceramic capacitors result in low, predictable output ripple. APPLICATIONS With their wide input range of 4V to 36V, the LT3474/ Automotive and Avionic Lighting LT3474-1 regulate a broad array of power sources, from Architectural Detail Lighting 5V logic rails to unregulated wall transformers, lead acid Display Backlighting batteries and distributed power supplies. A current mode Constant Current Sources PWM architecture provides fast transient response and L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. cycle-by-cycle current limiting. Frequency foldback and True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are thermal shutdown provide additional protection. the property of their respective owners. Patent Pending TYPICAL APPLICATION Step-Down 1A LED Driver Ef ciency 95 V IN V = 12V IN 5V TO 36V TWO SERIES CONNECTED 90 WHITE 1A LEDS 0.22F V BOOST 2.2F IN 85 SHDN SW 10H LT3474 80 ONE WHITE 1A LED R BIAS T 75 REF OUT 70 DIMMING* V PWM ADJ 80.6k CONTROL 2.2F 65 V LED C 0.1F 60 GND LED1 55 0 200 400 800 1000 600 *SEE APPLICATIONS SECTION FOR DETAILS LED CURRENT (mA) 3474 TA01a 3474 G02 3474fd 1 EFFICIENCY (%)LT3474/LT3474-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) V Pin ........................................................(0.3V), 36V IN BIAS Pin ....................................................................25V TOP VIEW BOOST Pin Voltage ...................................................51V DNC* 1 16 DNC* BOOST above SW Pin ...............................................25V OUT 2 15 GND OUT, LED Pins (LT3474) ............................................15V LED 3 14 PWM OUT, LED Pins (LT3474-1) .........................................26V V 4 17 13 V IN ADJ PWM Pin ...................................................................10V SW 5 12 V C V Pin .....................................................................6V ADJ BOOST 6 11 REF V , REF, R Pins ..........................................................3V BIAS 7 10 SHDN C T SHDN Pin ...................................................................V GND 8 9 R T IN BIAS Pin Current .........................................................1A FE PACKAGE 16-LEAD PLASTIC TSSOP Maximum Junction Temperature (Note 2)............. 125C = 8C/W, = 40C/W JC JA Operating Temperature Range (Note 3) EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB LT3474E, LT3474E-1 ............................ 40C to 85C *DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS. LT3474I, LT3474I-1 ............................ 40C to 125C Storage Temperature Range ................... 65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3474EFE PBF LT3474EFE TRPBF 3474EFE 16-Lead TSSOP 40C to 85C LT3474IFE PBF LT3474IFE TRPBF 3474IFE 16-Lead TSSOP 40C to 125C LT3474EFE-1 PBF LT3474EFE-1 TRPBF 3474EFE-1 16-Lead TSSOP 40C to 85C LT3474IFE-1 PBF LT3474IFE-1 TRPBF 3474IFE-1 16-Lead TSSOP 40C to 125C Consult LTC Marketing for parts speci ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based nish parts. For more information on lead free part marking, go to: