AATIAN55 Datasheet, PDF (2/4 Pages) SiGe Semiconductor, Inc. – Driving Color RGB LEDs with the AAT3123

AN-103
AAT3123 Application Note
RGB LED
4.0
Blue
3.5
3.0
Green
2.5
Red
2.0
1.5
1.0
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
I_D
Figure 2: Forward Voltage Versus Current Characteristic Curve
for an RGB Color LED Used in this Application Discussion.
Application Solution
The forward voltage drops for each LED within the RGB LED need to be equalized in order to match LED per-
formance over the AAT3123 operating range. Adding a ballast resistor to the red LED will help equalize the
LED output red color shift when the AAT3123 is operated in or near the dropout region of its output constant
current sources. See Figure 3.
VBATTERY
VIN
C1+
CIN
1µF
COUT
1µF
EN/SET
VOUT
C1-
C2+
AAT3123
C2-
D1
D2
D3
D4
EN/SET
GND
Enable Red
Enable Green
Enable Blue
C1
1µF
C2
1µF
RGB LED
RED GRN BLU
RBAL
Figure 3: AAT3123 RGB Driver Application With a Color Matching Ballast Resistor for the Red LED.
2
AN-103.2005.01.1.0