LT3922 36V, 2A Synchronous Step-Up LED Driver FEATURES DESCRIPTION n 2.5% LED Current Regulation The LT 3922 is a monolithic, synchronous, step-up DC/ n 2% Output Voltage Regulation DC converter that utilizes fixed-frequency, peak current n control and provides PWM dimming for a string of LEDs. 5000:1 PWM Dimming at 100Hz n The LED current is programmed by an analog voltage or 128:1 Internal PWM Dimming n the duty cycle of pulses at the CTRL pin. The LT3922 will Spread Spectrum Frequency Modulation n maintain 2.5% current regulation through an external Silent Switcher Architecture for Low EMI n sense resistor over a wide range of output voltages. Operates in Boost, Buck Mode and Buck-Boost Mode n 2.8V to 36V Input Voltage Range The switching frequency is programmable from 200kHz n Up to 34V LED String Voltage to 2MHz by an external resistor at the RT pin or by an n 2A, 40V Internal Switches external clock applied at the SYNC/SPRD pin. With the n 200kHz to 2MHz with SYNC Function optional spread spectrum frequency modulation enabled, n Analog or Duty Cycle LED Current Control the frequency varies from 100% to 125% to reduce EMI. n Open/Short LED Protection and Fault Indication The LT3922 also includes a driver for an external high n Thermally Enhanced 28-Lead (4mm 5mm) QFN side PMOS for PWM dimming and an internal PWM signal generator for analog control of PWM dimming when an external signal is not available. APPLICATIONS n Automotive and Industrial Lighting Additional features include an accurate external reference n Machine Vision voltage for use with the CTRL and PWM pins, an LED current monitor, an accurate EN/UVLO pin threshold, All registered trademarks and trademarks are the property of their respective owners. open-drain fault reporting for open-circuit and short-circuit load conditions, and thermal shutdown. TYPICAL APPLICATION 2MHz, 93% Efficient 10W (30V, 333mA) Boost LED Driver Efficiency vs V IN L1 100 33nF 4.7H V = 30V LED f = 2MHz SW 95 V IN SW BST V IN V OUT 8V TO 27V 90 1M 0.47F 4.7F GND EN/UVLO 0.47F 85 365k V OUT 1M OVLO 80 LT3922 59.0k FB 4.7F 33.2k 75 GND 100% PWM Duty Cycle V REF 70 1F ISP 100k 6 9 12 15 18 21 24 27 30 V (V) IN 300m ANALOG DIM CTRL 3922 TA01b PWM DIM PWM ISN SYNC/SPRD INTV CC 100k PWMTG M1 FAULT ISMON SS RT RP V C 2.2F 30V 333mA 10k 45.3k 10nF LED 2MHz 1nF 3922 TA01a Rev. B 1 Document Feedback For more information www.analog.com EFFICIENCY (%)LT3922 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW V and EN/UVLO ......................................................40V IN ISP, ISN, and V ....................................................40V OUT 28 27 26 25 24 23 ISP ISN .................................................................0.3V SW 1 22 GND CTRL and FB ............................................................3.3V BST 2 21 V OUT OVLO, PWM, SYNC/SPRD, and FAULT ........................6V INTV 3 20 PWMTG CC SS and V ................................................................3.3V C V 4 19 PWM IN 29 SW, BST, INTV , V , ISMON, PWMTG, GND CC REF EN/UVLO 5 18 RP RT, and RP ..................................................... (Note 2) OVLO 6 17 SYNC/SPRD Operating Junction Temperature Range (Notes 3, 4) V 7 16 RT REF CTRL 8 15 FAULT LT3922E/LT3922I .................................. 40 to 125C 9 10 11 12 13 14 LT3922H ................................................40 to 150C Storage Temperature Range ......................60 to 150C UFD PACKAGE 28-LEAD (4mm 5mm) PLASTIC QFN = 34C/W JA EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3922EUFD PBF LT3922EUFD TRPBF 3922 28-Lead (4mm 5mm) Plastic QFN 40C to 125C LT3922IUFD PBF LT3922IUFD TRPBF 3922 28-Lead (4mm 5mm) Plastic QFN 40C to 125C LT3922HUFD PBF LT3922HUFD TRPBF 3922 28-Lead (4mm 5mm) Plastic QFN 40C to 150C Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with TRMPBF suffix. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25C, V = 12V, V = 2V unless otherwise noted. A IN EN/UVLO PARAMETER CONDITIONS MIN TYP MAX UNITS Input Voltage Range 2.8 36 V V Pin Quiescent Current V = 1.5V, Not Switching 2.9 4 mA IN EN/UVLO V = 0.1V, Shutdown 1 A EN/UVLO EN/UVLO Threshold (Falling) 1.260 1.330 1.400 V EN/UVLO Rising Hysteresis 25 mV EN/UVLO Pin Current V = 1.2V 2 A EN/UVLO Input OVLO Threshold (Rising) 1.145 1.205 1.265 V Input OVLO Falling Hysteresis 50 mV OVLO Pin Current V = 1.0V 100 100 nA OVLO Rev. B 2 For more information www.analog.com ISP SW ISN SW V NC C FB NC SS V OUT ISMON GND