Features

• 3000:1 True Color PWM™ Dimming
• Wide Input Voltage Range: 4.5V to 80V
• Output Voltage Up to 80V
• Internal 3.3A/84V Switch
• Constant-Current and Constant-Voltage Regulation
• 250mV High Side Current Sense
• Drives LEDs in Boost, Buck Mode, Buck-Boost Mode, SEPIC or Flyback Topology
• Adjustable Frequency: 100kHz to 1MHz
• Open LED Protection
• Programmable Undervoltage Lockout with Hysteresis
• Constant-Voltage Loop Status Pin
• PWM Disconnect Switch Driver
• CTRL Pin Adjusts High Side Current Sense Threshold
• Low Shutdown Current: <1μA
• Programmable Soft-Start
• Available in the 36-Lead (5mm × 6mm) QFN Package

Typical Application

Description

The LT3956 is a DC/DC converter designed to operate as a constant-current source and constant-voltage regulator. It is ideally suited for driving high current LEDs. It features an internal low side N-channel power MOSFET rated for 84V at 3.3A and driven from an internal regulated 7.15V supply. The fixed frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages. A ground referenced voltage FB pin serves as the input for several LED protection features, and also makes it possible for the converter to operate as a constant-voltage source. A frequency adjust pin allows the user to program the frequency from 100kHz to 1MHz to optimize efficiency, performance or external component size.

The LT3956 senses output current at the high side of the LED string. High side current sensing is the most flexible scheme for driving LEDs, allowing boost, buck mode or buck-boost mode configuration. The PWM input provides LED dimming ratios of up to 3000:1, and the CTRL input provides additional analog dimming capability.