www.ams.com/DC-DC_Step-Up/AS1340

Revision 1.20

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AS1340

Datasheet - Application In form atio n

9.5 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 Figure 29).

Figure 29. LED Supply Application

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 Feedback Voltage VFB.

Calculate VOUT by:

Note:

The brightness of the LEDs can directly be adjusted by setting the current ILED via the corresponding R2.

Calculate R2 by:

Where:

VFB = 1.25V

n .... number of LED’s

1

EN

7,9

GND

2

VCC

8

FB

5

LX

On

Off

AS1340

L1

4.7µH

C1

0.1µF

D1

COUT

1µF

R2

100



3

SWVIN

6

SWOUT

4

POK

C1

0.1µF

ILED

VIN

= 2.7V

to 5.5V

(EQ 3)

VOUT

VF ILED

 n



VFB

+

=

(EQ 4)

ILED

VFB

R2

----------

=