High Current Synchronous Step-Down LED Driver Delivers 40A

The LT3744 is a fixed frequency synchronous step-down DC/DC controller designed to drive a LED load at up to 20A continuous or 40A pulsed. The peak current mode controller will maintain ±3% LED current regulation over a wide output voltage range, from VEE to V_IN. By allowing VEE to float to negative voltages, several LEDs in series can be driven from a single Li-Ion battery with a simple, single step-down output stage. The switching frequency is programmable from 100kHz to 1MHz through an external resistor.

The LT3744 from Linear Technology 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 makes it ideal for a wide variety of applications, including industrial, DLP projection and architectural lighting.

This device 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 160 watts from a 12V input. Delivering efficiencies as high as 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 V_EE to V_IN. By allowing V_EE to float to negative voltages, several LEDs can be driven from a single Li-Ion battery with a simple, single step-down output stage.

Additionally, this enables a unique 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 100kHz and 1MHz, optimizing efficiency while minimizing external component size. Combined with its 5mm x 6mm QFN package, the LT3744 offers a very compact 80 watt LED driver solution.

The LT3744 provides both PWM dimming and CTRL dimming, which offer 3,000:1 dimming capability for four LED current levels, ideal for color mixing applications, such as those required in DLP projectors. Similarly, its unique topology enables it to transition between two regulated LED currents in less than 2µsec, enabling more accurate color mixing in RGB applications. LED current accuracy of ±3% is maintained to offer the most accurate brightness of light emitted from the LED.

Additional features include output voltage regulation and open-LED and shorted-LED protection, an accurate external reference voltage, a control input for thermally derating regulation current, an accurate EN/UVLO pin, an open-drain output fault flag, OVLO, frequency synchronization, and thermal shutdown.

The regulated LED current is set with analog voltages at the CTRL pins while regulated voltage and overvoltage protection are set with a voltage divider from the output to the FB pin.

The LT3744 is available in 36-pin 5mm x 6mm QFN package. Two temperature grades are available, with operation from -40°C to 125°C (junction) for the extended and industrial grades. The 1,000 piece price starts at $4.55 each. All versions are available from stock.

The USA list pricing shown is for budgetary use only. International prices may differ due to local duties, taxes, fees and exchange rates.

For more information, visit www.linear.com/product/LT3744.

Summary of Features of the LT3744:

• Ideal for Driving up to 40A LEDs with a Single Stage
• Up to 3,000:1 PWM Dimming
• 20:1 Analog Dimming
• ±3% Current Regulation Accuracy
• ±3% Voltage Regulation Accuracy
• Unique Inverting Step-Down Topology Allows Single Common Anode Heat Sink to Be Used for RGB LEDs
• 3.3V to 36V Input Voltage Range
• Peak Current Mode with DC LED Current Sensing
• Open & Shorted LED Protection & Fault Reporting
• Floating LED Driver Allows Single Power Solution to Drive Multicolor LEDs or Single LED with Three Different Regulated Currents
• Thermally Enhanced 5mm × 6mm QFN 36-Lead Package

Typical Application