Introduction to the Constant Current, Constant Voltage Converter LT3956

describe

The LT®3956 is a DC/DC ^converter designed to act as a constant current source and constant voltage regulator. It is ideal for driving high current LEDs. The device features an internal low-side N-channel power MOSFET rated for 84V/3.3A and driven from an internal regulated 7.15V supply. The fixed frequency, current mode architecture enables 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 enables the converter to function as a constant voltage source. A frequency adjust pin allows the user to set the frequency from 100kHz to 1MHz to optimize efficiency, performance or external component size.

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

Features

● 3000:1 True Color PWMTM 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 detection

● Can drive LEDs in boost, buck mode, buck-boost mode, SEPIC or flyback topologies

● Adjustable frequency: 100kHz to 1MHz

● Open circuit LED protection

● Programmable undervoltage lockout with hysteresis

● Constant voltage loop status pin

● PWM Disconnect Switch Driver

● CTRL pin is responsible for adjusting the high-side current detection threshold

● Low shutdown current: <1μA

● Programmable soft start

● 36-pin (5mm x 6mm) QFN package

Encapsulation

Typical Applications

application

● High power LED

Battery charger

● Accurate current limited voltage regulator