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LED driver needs no external MCU, switch-mode converter

Posted: 11 Sep 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Maxim? MAX16806? LED driver?

Maxim Integrated Products has introduced the MAX16806, an EEPROM-programmable, 350mA, high-voltage (40V) linear, high-brightness LED driver. This IC can be programmed through an I?C interface to fold back the LED current if input voltage or LED temperature rises above the programmed threshold. Although a traditional architecture requires switch-mode converters to reduce power dissipation, the design of this LED driver manages total power dissipation in a lighting system, the company said, and thus eliminates the need for a switch-mode converter. Consequently, the device reduces both cost and EMI concerns for powering high-brightness LEDs. These features make the device suitable for lighting applications such as automotive interior and exterior lighting.

The automotive industry is replacing the existing incandescent lamps with white LEDs for dome and map lights. This change is done to create a technologically advanced image for the new cars. The LEDs need to work with the existing control module unit, and this poses a new problem for auto makers. The present theater dimming signal operates at very low frequency and causes the LEDs to blink noticeably during dimming. To eliminate this effect, the LED driver used to require a microcontroller to create a new PWM signal.

Key features
According to Maxim, MAX16806 has a unique design that eliminates the need for external controls. Its architecture has no need for a microcontroller's PWM signal because an on-board 200Hz ramp generator allows analog control for PWM or theater dimming effect. The device's high-voltage (40V rated) DIM pin can also sync with up to a 2kHz external PWM signal. The fast turn-on/off times ensure a wide dimming range, while the wave-shaping circuitry minimizes EMI. This simplifies production and reduces manufacturing cost, the company said. This devices uses one value of a current-sense resistor in conjunction with EEPROM-programmable current-sense reference to set the LED current for all LED bins.

LED brightness can be changed automatically, on-the-fly on this device, said Maxim, a feature that makes it especially versatile for demanding lighting applications that extend far beyond the automotive industry. Designers simply adjust the RGB LED current level dynamically through the I?C interface. This allows the creation of a wide range of colors for architectural or general lighting applications. Integrated debounce circuitry supplies the necessary wetting current for a momentary switch. This feature makes the device suitable for automotive dome- or map-lighting applications.

The MAX16805, a companion product, has many of the same features as the MAX16806, but is offered for applications that do not need LED current thermal foldback or wetting current and debounce circuitry for a momentary switch.

The MAX16806/MAX16805 are rated for operation over the automotive temperature range (-40C to 125C). They are available in a thermally enhanced, surface-mount 5-by-5mm, 20-pin TQFN Pb-free package rated at 2.67W power dissipation. Prices for the MAX16805 start at $1.42 and $1.49 for the MAX16806 (1,000-up, FOB USA).

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