LP3359 Datasheet, PDF (6/9 Pages) Lowpower Semiconductor inc – High performance, Current Source For Parallel White-LED Driver

equals 12.5kΩ.
LP3359
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.
Figure4. LED current setting example
which using a DC voltage to Rset
VADJ(V)
ILED(mA)
VADJ(V)
ILED(mA)
0
19.7
1.4
8.5
0.2
18.1
1.6
6.9
0.4
16.5
1.8
5.3
0.6
14.9
2
3.7
0.8
13.3
2.2
2.1
1
11.7
2.4
0.5
1.2
10.1
2.5
0
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.
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
LP3359-datasheet Ver.1.1 Nov.-2005
Figure 6. One Parallel Connected LED
6 -6