9

LTC3490

3490fa

TYPICAL APPLICATIO S

2-Cell Adjustable Amplitude LED Driver

+

+

SW

CAP

LED

2 NiMH OR

ALKALINE

CELLS

4.7

µF

LOBAT

3490 TA03

CTRL/SHDN

CELLS

1M

LUMILEDS

LUXEON

LXHL-BW02

GND

LTC3490

3.3

µH

ON/OFF

Soft Turn-Off LED Driver

+

SW

CAP

LED

1 NiMH OR

ALKALINE

CELL

4.7

µF

LOBAT

3490 TA04

CTRL/SHDN

CELLS

1M

ON/OFF

1

µF

LUMILEDS

LUXEON

LXHL-BW02

GND

LTC3490

3.3

µH

350mA

APPLICATIO S I FOR ATIO

Red Luxeon LEDs

The red, red-orange and amber Luxeon LEDs have a lower

forward voltage than the white, blue and green LEDs. Since

the LTC3490 internal circuitry is powered from the output,

it requires a minimum LED voltage of 2.5V for reliable

operation. The minimum forward voltage on the red LEDs

is only 2.31V. The LTC3490 requires an additional 190mV

for proper operation. In non-dimming applications, this can

be accomplished with a 0.6

Ω resistor in series with the

LED. The resistor voltage drops too low in dimming appli-

cations, so a Schottky diode is recommended to keep

sufficient voltage at the output at lower currents.