Power Electronics

LED Driver Eliminates Switch-Mode Converter

Maxim Integrated Products’ MAX16806 is an EEPROM-programmable, 350-mA, high-voltage (40-V) linear, high-brightness LED driver. This IC can be programmed through an I2C 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 MAX16806 LED driver manages total power dissipation in a lighting system, and thus eliminates the need for a switch-mode converter. Consequently, the MAX16806 reduces both cost and EMI concerns for powering high-brightness LEDs.

The automotive industry is replacing the existing incandescent lamps with white LEDs for dome and map lights. 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.

The architecture for the MAX16806 also eliminates the need for a microcontroller's PWM signal, because an on-board 200-Hz ramp generator allows analog control for PWM or theater dimming effect. The device's high-voltage (40-V rated) DIM pin can also sync with up to a 2-kHz external PWM signal. The fast turn-on/off times ensure a wide dimming range, while the wave-shaping circuitry minimizes EMI.

The MAX16806 was also designed to simplify production and reduce manufacturing cost. This LED driver 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.

Integrated debounce circuitry supplies the necessary wetting current for a momentary switch. This feature makes the MAX16806 an ideal LED driver for automotive dome- or map-lighting applications. The device requires minimum external components to implement the LED driver circuit, making it a cost effective solution for many 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 driver combines a low-voltage (204-mV) current-sense reference with differential LED current sensing to provide load accuracy of ±3.5%. This current accuracy allows consistent brightness for all light assemblies. The device's low-dropout pass element (0.5-V typical) and current-sense reference minimize power dissipation. Output voltage is rated to 39 V and allows the MAX16806 to drive multiple LEDs in series. The driver has overtemperature and short-circuit protection, important safeguards for lighting applications.

The MAX16806/MAX16805 are rated for operation over the automotive temperature range (-40°C to +125°C). They are available in a thermally enhanced, surface-mount, 5-mm x 5-mm, 20-pin TQFN lead-free package rated at 2.67 W power dissipation. Prices for the MAX16805 start at $1.42 and $1.49 for the MAX16806 for 1000 pieces.

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