2-String × 60mA, 2MHz Step-Up LED Driver with ±2% Current Matching

The LT3909 is a 2-string × 60mA LED driver with a fixed 2MHz step-up DC/DC converter capable of driving up to 36V of LEDs. Each LED string contains an accurate high-side current source with ±2% current matching. Output voltage adapts to variations in LED VF for optimum efficiency.

Maximum LED current can be programmed from 10mA to 60mA per string using a single resistor. LED brightness can be reduced with analog dimming (up to 10:1) or with PWM dimming (up to 40,000:1 at 100Hz, up to 160:1 at 25kHz) (independent of leakage at VOUT). The LED pins can be paralleled for higher LED current.

Additional features include: programmable maximum VOUT for open LED protection, a fault flag to indicate open-LED or LED-short-to-GND and an internal regulation loop to safely limit junction temperature. The LT3909 also includes internal compensation, internal soft-start and micropower shutdown. The LT3909 is available in the 12-pin (3mm × 3mm) DFN and 12-pin MSOP packages.

Applications

* PDAs, Handheld Computers

* GPS Receivers

* Automotive Displays

* High Contrast Instrument Clusters

* Up to 36V of LEDs, 2-String × 60mA LED Driver

* Wide Input Range: 2.9V to 40V

* Up to 40,000:1 PWM Dimming (250ns LED On-Time) (Independent of Leakage at VOUT)

* ±2% LED Current Matching (Typ ±0.3%)

* Integrated Schottky Diode

* Internal 400mΩ, 40V, 1A Switch

* Single Resistor Sets LED Current (10mA to 60mA) for Both High-Side Current Sources

* Output Adapts to LED VF for Optimum Efficiency

* LED Current Regulated Even for VIN > VOUT

* Fault Flag + Protection for Open-LED and LED-Short-to- GND (Other String Remains in Regulation)

* Programmable Maximum VOUT (Regulated)

* Internal Compensation, Soft-Start and Thermal Regulation

* Accurate EN/UVLO Threshold

* Fixed 2MHz Switching Frequency