Synchronous step-down LED driver delivers up to 40A pulsed

March 30, 2015 // By Graham Prophet
LT3744 is a synchronous step-down DC/DC converter designed to deliver constant current to drive high current LEDs. Its 3.3V to 36V input voltage range suits it for applications including industrial, DLP projection and architectural lighting.

It uses two external switching MOSFETs, delivering up to 20A (80W) of continuous LED current from a nominal 12V input. In pulsed LED applications, it can deliver up to 40A of LED current or 160W from a 12V input. Delivering efficiencies up to 95%, it can eliminate the need for external heat sinking.

The LT3744’s peak current mode controller maintains ±3% LED current regulation over a wide voltage range from VEE to VIN. By allowing VEE to float to negative voltages, several LEDs can be driven from a single Li-Ion battery with a simple, single step-down output stage. This enables an inverting step-down topology which allows a single common anode heat sink to be used for RGB LEDs. A frequency adjust pin allows the user to program the frequency between 100 kHz and 1MHz, optimising efficiency while minimising external component size. Combined with its 5 x 6 mm QFN package, the LT3744 offers a very compact 80W LED driver solution.

The LT3744 provides both PWM dimming and CTRL dimming, which offer 3,000:1 dimming capability for four LED current levels, for colour mixing applications, such as those required in DLP projectors. Its topology enables it to transition between two regulated LED currents in less than 2 µsec, enabling more accurate colour mixing in RGB applications. LED current accuracy of ±3% is maintained to offer the most accurate brightness of light emitted from the LED. Features include output voltage regulation and open-LED and shorted-LED protection, open-drain output fault flag, frequency synchronisation and thermal shutdown.

In a 36-pin 5 x 6 mm QFN package, two temperature grades are available, with operation from -40°C to 125°C (junction) for the extended and industrial grades; its price starts at $4.55 (1000).

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