The LT®3743 is a fixed frequency synchronous step-down DC/DC controller designed to drive high current LEDs. The average current mode controller will maintain inductor current regulation over a wide output voltage range of 0V to (VIN – 2V). LED dimming is achieved through analog dimming on the CTRL_L, CTRL_H and CTRL_T pins and with PWM dimming on the PWM and CTRL_SEL pins. Through the use of externally switched load capacitors, the LT3743 is capable of changing regulated LED current levels within several μs, providing accurate, high speed PWM dimming between two current levels. The switching frequency is programmable from 200kHz to 1MHz through an external resistor on the RT pin.
Additional features include voltage regulation and overvoltage protection set with a voltage divider from the output to the FB pin. Overcurrent protection is provided and set by the CTRL_H pin.
- DLP Projectors
- High Power Architectural Lighting
- Laser Diodes
- PWM Dimming Provides Up to 3000:1 Dimming Ratio
- CTRL_SEL Dimming Provides Up to 3000:1 Dimming Ratio Between Any Current
- Three-State Current Control for Color Mixing
- ±6% Current Regulation Accuracy
- 6V to 36V Input Voltage Range
- Average Current Mode Control
- 2μs Maximum Recovery Time Between Any Current Regulation State
- <1μA Shutdown Current
- Output Voltage Regulation and Open-LED Protection
- Thermally Enhanced 4mm × 5mm QFN and 28-Pin FE Package
So far, most of this growth has been dominated by lower current LEDs, primarily in the 100mA to 500mA range. However, higher current LED applications, requiring 2A to 20A of current to drive a single LED are becoming more common place.
The first of these were found in automotive headlights but they can now be found in applications ranging from high power architectural lighting to high performance DLP (Digital Light Projection) projectors.
The enhanced performance of these applications will continue to fuel the high growth rate of high current LEDs in the foreseeable future
Emerging High Power LED Applications
The introduction of high current LEDs enabled high power lighting applications to use them, replacing relatively inefficient incandescent bulbs.
In applications such as architectural lighting and DLP projectors, which traditionally require 500watt to 1,000W halogen bulbs, 20A LEDs can offer the same light output (in lumens) but only require 20% of the electrical power.
In architectural applications, the LED driver must be very efficient and offer wide dimming ratios to maintain a constant light output in a wide array of ambient conditions.
In high end DLP projection applications, an array of red, green and blue (RGB) LEDs replaces the traditional halogen bulb, color wheel and array of mirrors (mems).
However, in order to mix colors accurately, a LED driver must be able to rapidly switch between two disparate regulated peak current states and overlay PWM dimming without disruption.
Designing high current LED driver ICs that are capable of meeting these demanding speed and accuracy requirements while optimizing overall efficiency, has posed many new challenges for IC designers
For more read: High LEDs brightness get power drive