Datasheet

9
LTC3490
3490fa
TYPICAL APPLICATIO S
U
2-Cell Adjustable Amplitude LED Driver
+
+
SW
CAP
LED
2 NiMH OR
ALKALINE
CELLS
4.7µF
LOBAT
3490 TA03
V
IN
CTRL/SHDN
CELLS
1M
LUMILEDS
LUXEON
LXHL-BW02
GND
LTC3490
3.3µH
ON/OFF
Soft Turn-Off LED Driver
+
SW
CAP
LED
1 NiMH OR
ALKALINE
CELL
4.7µF
LOBAT
3490 TA04
V
IN
CTRL/SHDN
CELLS
1M
ON/OFF
1µF
LUMILEDS
LUXEON
LXHL-BW02
GND
LTC3490
3.3µH
350mA
APPLICATIO S I FOR ATIO
WUUU
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 0.6Ω 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.