TABLE 2. LED Current when using the BRGT input with BR-ON = V

IN

R

Ω)

4.99k

Ω

6.25k

Ω

8.25k

Ω

12.4k

Ω

VBRGT(V)

I

I

I

I

0.0

0.1

0.1

0.1

0.1

0.5

4.1

3.3

2.5

1.6

1.0

8.1

6.7

4.9

3.3

1.5

12.2

10.0

7.4

4.9

2.0

16.3

13.3

9.9

6.6

2.5

20.4

16.7

12.3

8.2

3.0

24.5

20.0

14.8

9.8

LED SELECTION

The LM3595 is designed to drive white-LEDs with a typical

forward voltage of 3.0V to 4.0V. The maximum LED forward

voltage that the LM3595 can accommodate is highly depen-

dant upon V

Capability for more information on finding maximum V

For applications that demand color and brightness matching,

care must be taken to select LEDs from the same chroma-

ticity group. Forward current matching is assured over the

LED process variations due to the constant current outputs

of the LM3595.

TABLE 3. White LED Selection:

Component Manufacture Contact

Manufacturer

Contact

Osram

www.osram-os.com

Nichia

www.nichia.com

PARALLEL OUTx OUTPUTS FOR INCREASED

CURRENT DRIVE

Outputs OUT1 through OUT4 may be connected together in

any combination to drive higher currents through fewer

LEDs. For example in Figure 1, outputs OUT1 and OUT2 are

connected together to drive one LED while OUT3 and OUT4

are connected together to drive a second LED.

With this configuration, two parallel current sources of equal

value provide current to each LED. R

therefore be chosen so that the current through each output

is programmed to 50% of the desired current through the

parallel connected LEDs. For example, if 30mA is the de-

sired drive current for 2 parallel connected LEDs, R

V

the outputs is 15mA. Other combinations of parallel outputs

may be implemented in similar fashions, such as in Figure 2.

Connecting outputs in parallel does not affect internal opera-

tion of the LM3595 and has no impact on the Electrical

Characteristics and limits previously presented. The avail-

able diode output current, maximum diode voltage, and all

other specifications provided in the Electrical Characteristics

table apply to parallel output configurations, just as they do

to the standard 4-LED application circuit.

POWER DISSIPATION

The maximum allowable power dissipation that this package

is capable of handling can be determined as follows:

P

θ

JA

Where T

ambient temperature, and

θ

JA

is the junction-to-ambient

thermal resistance of the specified package. The LM3595

come in the LLP-10 package that has a junction-to-ambient

thermal resistance (

θ

θ

highly dependant upon the layout of the PC board (See the

PCB Layout Considerations section of this datasheet for

more information). The actual power dissipated by the

LM3595 follows the equation:

P

Where N equals the number of active outputs, V

LED forward voltage, and I

20072215

FIGURE 1. Two Parallel Connected LEDs

20072216

FIGURE 2. One Parallel Connected LED

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