LP3359 datasheet(6/9 Pages) POWER

6 / 9 page

LP3359

LP3359-datasheet

Ver.1.1

Nov.-2005

-6

equals 12.5kΩ.

Figure4. LED current setting example

which using a DC voltage to Rset

VADJ(V)

0.2

0.4

0.6

0.8

1.2

ILED(mA)

19.7 18.1 16.5 14.9 13.3 11.7 10.1

VADJ(V)

1.4

1.6

1.8

2.2

2.4

2.5

ILED(mA)

8.5

6.9

5.3

3.7

2.1

0.5

LED Selection

The LP3359 is designed to drive white-LEDs with a typical

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

voltage that the LP3359 can accommo -date is highly

dependant upon VIN and ILEDX (See the section on Output

Current Capability for more information on finding maximum

VLEDX.) For applications that demand color and brightness

matching, care must be taken to select LEDs from the same

chromaticity group. Forward current matching is assured over

the LED process variations due to the constant current outputs

of the LP3359.

Parallel LEDx Outputs for Increased Current Driver

Outputs LED1 through LED4 may be connected together in

any combination to drive higher currents through fewer

LEDs. For example in Figure 5, outputs LED1 and LED2 are

connected together to drive one LED while LED3 and LED4

are connected together to drive a second LED.

Figure 5. Two Parallel Connected LEDs

With this configuration, two parallel current sources of equal

value provide current to each LED. RSET should 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 desired drive current for 2

parallel connected LEDs, RSET should be selected so that the

current through each of the outputs is 15mA. Other

combinations of parallel outputs may be implemented in

similar fashions, such as in Figure 6.

Figure 6. One Parallel Connected LED

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