LT3475/LT3475-1 Dual Step-Down 1.5A LED Driver FEATURES DESCRIPTIO TM True Color PWM Delivers Constant Color with The LT 3475/LT3475-1 are dual step-down DC/DC 3000:1 Dimming Range converters designed to operate as a constant-current Wide Input Range: 4V to 36V Operating, 40V source. An internal sense resistor monitors the output Maximum current allowing accurate current regulation ideal for driving high current LEDs. The high side current sense al- Accurate and Adjustable Control of LED Current lows grounded cathode LED operation. High output current from 50mA to 1.5A accuracy is maintained over a wide current range, from High Side Current Sense Allows Grounded Cathode 50mA to 1.5A, allowing a wide dimming range. Unique LED Operation PWM circuitry allows a dimming range of 3000:1, avoid- Open LED (LT3475) and Short Circuit Protection ing the color shift normally associated with LED current LT3475-1 Drives LED Strings Up to 25V dimming. Accurate and Adjustable 200kHz to 2MHz Switching Frequency The high switching frequency offers several advantages, Anti-Phase Switching Reduces Ripple permitting the use of small inductors and ceramic capaci- Uses Small Inductors and Ceramic Capacitors tors. Small inductors combined with the 20 lead TSSOP Available in the Compact 20-Lead TSSOP Thermally surface mount package save space and cost versus Enhanced Surface Mount Package alternative solutions. The constant switching frequency U combined with low-impedance ceramic capacitors result APPLICATIO S in low, predictable output ripple. Automotive and Avionic Lighting With its wide input range of 4V to 36V, the LT3475/LT3475-1 Architectural Detail Lighting regulate a broad array of power sources. A current mode Display Backlighting PWM architecture provides fast transient response and Constant-Current Sources cycle-by-cycle current limiting. Frequency foldback and , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. thermal shutdown provide additional protection. All other trademarks are the property of their respective owners. Patents Pending. TYPICAL APPLICATIO Dual Step-Down 1.5A LED Driver Ef ciency V IN 5V TO 36V 4.7F 95 V SHDN IN V = 12V TWO SERIES CONNECTED IN BOOST1 BOOST2 WHITE 1.5A LEDS 90 0.22F 0.22F LT3475 10H 10H 85 SW1 SW2 80 SINGLE WHITE 1.5A LED OUT1 OUT2 75 LED1 LED2 *DIMMING DIMMING* 70 PWM1 PWM2 CONTROL CONTROL V V C1 C2 65 REF R T 2.2F 0.1F 0.1F 2.2F 60 1.5A LED 1.5A LED V V ADJ1 ADJ2 CURRENT CURRENT 24.3k GND 55 0 0.5 1 1.5 LED CURRENT (A) 3475 TA01 *SEE APPLICATIONS SECTION FOR DETAILS f = 600kHz SW 3475 TA01b 3475fb 1 EFFICIENCY (%) U ULT3475/LT3475-1 ABSOLUTE AXI U RATI GS PIN CONFIGURATION (Note 1) TOP VIEW V Pin .........................................................(-0.3V), 40V IN OUT1 1 20 PWM1 BOOST Pin Voltage ...................................................60V LED1 2 19 V ADJ1 BOOST Above SW Pin ...............................................30V BOOST1 3 18 V C1 SW1 4 17 REF OUT, LED, Pins (LT3475) ...........................................15V V 5 16 SHDN IN OUT, LED Pins (LT3475-1) .........................................25V 21 V 6 15 GND IN PWM Pin ...................................................................15V SW2 7 14 R T V Pin ......................................................................6V BOOST2 8 13 V ADJ C2 V , R , REF Pins ..........................................................3V LED2 9 12 V ADJ2 C T 10 OUT2 11 PWM2 SHDN Pin ...................................................................V IN Maximum Junction Temperature (Note 2)............. 125C FE PACKAGE 20-LEAD PLASTIC TSSOP Operating Temperature Range (Note 3) T = 125C, = 30C/W, = 8C/W JMAX JA JC LT3475E/LT3475E-1 ............................. 40C to 85C EXPOSED PAD (PIN 21) IS GROUND AND MUST BE ELECTRICALLY CONNECTED TO THE PCB. LT3475I/LT3475I-1 ............................. 40C to 125C Storage Temperature Range ................... 65C to 150C Lead Temperature Range (Soldering, 10 sec) ....... 300C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3475EFE PBF LT3475EFE TRPBF LT3475EFE 20-Lead Plastic TSSOP 40C to 85C LT3475IFE PBF LT3475IFE TRPBF LT3475IFE 20-Lead Plastic TSSOP 40C to 125C LT3475EFE-1 PBF LT3475EFE-1 TRPBF LT3475FE-1 20-Lead Plastic TSSOP 40C to 85C LT3475IFE-1 PBF LT3475IFE-1 TRPBF LT3475FE-1 20-Lead Plastic TSSOP 40C to 125C Consult LTC Marketing for parts speci ed with wider operating temperature ranges. *The temperature grade is identi ed by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based nish parts. For more information on lead free part marking, go to: