Datasheet LT3956 (Analog Devices)

LT3956 80VIN, 80VOUT Constant-Current, Constant-Voltage Converter FeaTures DescripTion n
3000:1 True Color PWMTM Dimming
The LT®3956 is a DC/DC converter designed to operate as n
Wide Input Voltage Range: 4.5V to 80V
a constant-current source and constant-voltage regulator. n
Output Voltage Up to 80V
It is ideally suited for driving high current LEDs. It features n
Internal 3.3A/84V Switch
an internal low side N-channel power MOSFET rated for n
Constant-Current and Constant-Voltage Regulation
84V at 3.3A and driven from an internal regulated 7.15V n 250mV High Side Current Sense supply. The fixed frequency, current-mode architecture n Drives LEDs in Boost, Buck Mode, Buck-Boost Mode, results in stable operation over a wide range of supply SEPIC or Flyback Topology and output voltages. A ground referenced voltage FB pin n Adjustable Frequency: 100kHz to 1MHz serves as the input for several LED protection features, n Open LED Protection and also makes it possible for the converter to operate n Programmable Undervoltage Lockout with Hysteresis as a constant-voltage source. A frequency adjust pin n Constant-Voltage Loop Status Pin allows the user to program the frequency from 100kHz n PWM Disconnect Switch Driver to 1MHz to optimize efficiency, performance or external n CTRL Pin Adjusts High Side Current Sense Threshold component size. n Low Shutdown Current: <1µA The LT3956 senses output current at the high side of the n Programmable Soft-Start LED string. High side current sensing is the most flexible n Available in the 36-Lead (5mm × 6mm) QFN Package scheme for driving LEDs, allowing boost, buck mode or applicaTions buck-boost mode configuration. The PWM input provides LED dimming ratios of up to 3000:1, and the CTRL input n High Power LED provides additional analog dimming capability. n Battery Charger L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the n Accurate Current Limited Voltage Regulator property of their respective owners. Protected by U.S. Patents, including 7199560 and 7321203. Typical applicaTion
94% Efficient 25W White LED Headlamp Driver Efficiency vs VIN
VIN, 6V TO 60V 22µH D1 (80V TRANSIENT) 100 2.2µF 332k 2.2µF V s IN SW s EN/UVLO PGND 96 100k VREF ISP 332k LT3956 0.68Ω 370mA 92 CTRL INTVCC 40.2k ISN 1M 88 100k FB EFFICIENCY (%) VMODE 16.2k 25W LED STRING PWM 84 SS RT PWMOUT VC GND INTVCC 80 28.7k 34k INTV 0 20 40 60 80 375kHz CC VIN (V) 47nF 4.7nF 4.7µF M1 3956 TA01b 3956 TA01a 3956f 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 Application Package Description Typical Application Related Parts