AL5809

Document number: DS36625 Rev. 5 - 2

5 of 16

www.diodes.com

December 2016

© Diodes Incorporated

AL5809

Application Information

Description

The AL5809 is a constant current Linear LED driver and can be placed in series with LEDs as a High Side or a Low Side constant current

regulator. The AL5809 offers various current settings from 15mA up to 150mA and different current settings available upon request (contact

Diodes local sales office at http://www.diodes.com).

The AL5809 contains a Low-Dropout regulator which provides power to the internal Current regulation control block. A fixed preset LED current

setting resistor sets the reference current of the Current regulation block. The LED current setting resistor varies with each variant of the AL5809.

An accurate current mirror within the Current regulation control block increases the reference current to the preset LED current of the AL5809.

Simple LED String

The AL5809 can be placed in series with LEDs as a Low Side/High Side constant current regulator. The number of the LEDs can vary from one

to as many as can be supported by the input supply voltage. The designer needs to calculate the maximum voltage between In and Out by

taking the maximum input voltage minus the voltage across the LED string (Figures 1 & 2).

VIN

Low Side LED String

IN

OUT

1

2

AL5809

Figure 1 Low Side LED String Tapping

VIN

High Side LED String

IN

OUT

1

2

AL5809

Figure 2 High Side LED String Tapping

The AL5809 can also be used on the high side of the LEDs, see Figure 2. The minimum system input voltage can be calculated by:

The LED current can be increased by connecting two or more AL5809 in parallel in Figure 3.

VIN

IN

OUT

IN

OUT

. . .

AL5809

AL5809

2

2

1

1

AL5809

AL5809

VIN

IN

OUT

IN

OUT

. . .

1

1

2

2

(a)Low Side Configuration

(b) High Side Configuration

Figure 3 Higher LED Current by Parallel Configuration of AL5809