Datasheet LT3922 (Analog Devices)

LT3922 36V, 2A Synchronous Step-Up LED Driver
FeaTures DescripTion
n
±2% 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
5000:1 PWM Dimming at 100Hz
control and provides PWM dimming for a string of LEDs. n
128:1 Internal PWM Dimming
The LED current is programmed by an analog voltage or n
Spread Spectrum Frequency Modulation
the duty cycle of pulses at the CTRL pin. The LT3922 will n
Silent Switcher
®
Architecture for Low EMI
maintain ±2% current regulation through an external sense n
Operates in Boost, Buck Mode and Buck-Boost Mode
resistor over a wide range of output voltages. 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
applicaTions
external signal is not available. 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 L, LT, LTC, LTM, Linear Technology, the Linear logo and Silent Switcher are registered current monitor, an accurate EN/UVLO pin threshold, trademarks of Linear Technology Corporation. All other trademarks are the property of their open-drain fault reporting for open-circuit and short-circuit respective owners. Protected by U.S. Patents, including 7199560, 7321203, and other patents pending. load conditions, and thermal shutdown.
Typical applicaTion 2MHz, 93% Efficient 10W (30V, 333mA) Boost LED Driver Efficiency vs VIN
L1 0.1µF 100 4.7µH VLED = 30V fSW = 2MHz 95 VIN VIN SW BST 8V TO 27V VOUT 4.7µF 1M 0.47µF 90 GND EN/UVLO 0.47µF 85 365k VOUT OVLO 1M EFFICIENCY (%) LT3922 80 59.0k FB 4.7µF 33.2k 75 V GND 100% PWM Duty Cycle REF 1µF 70 100k ISP 6 9 12 15 18 21 24 27 30 V ANALOG DIM CTRL 300mΩ IN (V) 3922 TA01b PWM DIM PWM ISN SYNC/SPRD INTVCC 100k PWMTG M1 FAULT ISMON SS RT RP VC 2.2µF 30V 45.3k 10k 333mA 10nF LED 2MHz 1nF 3922 TA01a 3922fa For more information www.linear.com/LT3922 1 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts