AS1340
Datasheet - Application Information
LED Power Supply Application
The AS1340 can also be used for driving LEDs. Just simply connect the LEDs between the pins LX and FB. (see Fig-
ure 29).
Figure 29. LED Supply Application
L1
4.7µH
3
6
SWVIN
SWOUT
2
D1
VIN = 2.7V
to 5.5V
5
VCC
C1
0.1µF
LX
COUT
1µF
4
8
AS1340
POK
FB
ILED
1
On
Off
R2
100Ω
EN
7,9
GND
The output voltage is adjusted automatically to the required voltage of the LEDs. This voltage depends on the forward
voltage (VF) of the used LEDs and the Feeback Voltage VFB.
Calculate VOUT by:
VOUT = VF(ILED) × n + VFB
(EQ 3)
Note: The brightness of the LEDs can directly be adjusted by setting the current ILED via the corresponding R2.
Calculate R2 by:
VFB
R2
----------
ILED =
(EQ 4)
Where:
VFB = 1.25V
n .... number of LED’s
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