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Optoelectronics/Displays??

LED drivers address mercury-free requirement

Posted: 14 Nov 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Maxim? LED drivers? high-brightness LED? white LED? RGB LED?

Maxim Integrated Products has introduced the MAX16807-MAX16810 family of multichannel, constant-current, linear LED drivers with an integrated switch-mode voltage controller. The company said these devices are the first fully integrated, high-brightness LED drivers that address industry needs for mercury-free, high-contrast lighting in displays. They also promise accurate and matched constant-current control in multiple LED strings for automotive and other premium LCD displays, such as in notebook and desktop monitors, LCD TVs and industrial LCD panels. Produced with an environmentally friendly, Pb-free technology, these LED drivers are packaged in the industry's smallest footprint, Maxim said.

The new LED drivers feature a current-mode PWM controller and provide eight or 16 open-drain, constant-current sinking, parallelable outputs, which are resistor-programmable up to 55mA per channel and rated for 36V continuous operation. The PWM controller delivers up to 1A of load current at the maximum 40V output voltage and up to 92 percent overall efficiency when using an external MOSFET.

The MAX16807/MAX16808 operate either in standalone mode or with an MCU using a 25Mbps, industry-standard (shift-register-plus-latch-type), 4-wire serial interface. A dedicated dimming input provides fast turn-off and turn-on of all LED channels, thus enabling dimming ratios up to 5000:1. The drivers feature an adjustable frequency range of 25kHz to 1MHz that allows design optimization based on tradeoffs in efficiency, space (by using miniature inductor and capacitors), and EMI minimization.

LED driver design
The move to remove mercury-based light sources in motor vehicles will force the automotive industry to replace the existing CCFL-based displays for navigation and infotainment with white-LED backlights. LEDs as light sources offer distinct advantages in multicolor, adjustable architectural and automotive lighting applications.

The novel architecture for MAX16807-MAX16810 drivers eliminates the need for multiple other ICs and discrete power devices, Maxim said. Instead, these new LED drivers integrate switch-mode controller, constant-current multichannel LED regulators with high-voltage MOSFET pass elements and interface circuitry.

These new devices were likewise designed to simplify production and reduce manufacturing cost. They use one value of a current-setting resistor for multiple channels. Implemented with a common bandgap reference design, this single resistor ensures LED current accuracy and precise color matching. Necessary high performance is achieved, production time saved and costs lowered, the company said.

Topology that's flexible yet highly integrated within the industry-smallest packages makes these ICs suitable for a full range of LCD display products from 3.5 inches to 50 inches. High-output voltage rating enables the highest number of white or RGB LEDs connected in series in each string. This multistring, multiple-LEDs-per-string topology is attractive in decorative and mood lighting applications in architecture and motor vehicles.

These new LED drivers operate over the -40C to 125C temperature range and are available in a thermally enhanced, 28-pin, exposed pad TSSOP package (MAX16807, MAX16808) and 38-pin, 7-by-5mm TQFN package (MAX16809, MAX16810). Pricing starts at $2.71 for MAX16809/10 and $2.04 for MAX16807/08 (1,000-up, FOB USA).




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