AAT3128
RGB LED Fashion Lighting Controller
EN/SET Timing
t
HI
t
LO
t
OFF
EN/SET
Code
OFF
1
2
3
OFF
Figure 1: S
2
Cwire Timing Diagram.
Application Information
R
SET
Selection
The maximum output current for current sources
ISRC1 and ISRC2 is programmed by the R
SET
resistor. A nominal value of 38.3kΩ will set each
current source output to 60mA each. Lower maxi-
mum current levels may be programmed by reduc-
ing the value of R
SET
. Refer to Table 3 for R
SET
resistor values to set the maximum brightness con-
stant current rounded off to the closest 1% value.
Current Source
Output (mA)
60
50
40
30
20
10
RGB LED Selection
The AAT3128 is specifically intended for driving
RGB color LEDs. However, the device design will
allow the AAT3128 to drive most types of LEDs with
forward voltage specifications ranging from 1.0V to
5.0V. The two current sink outputs provide up to
60mA each and may be paralleled to drive high-
current LEDs up to 120mA without complication.
Most RGB color LEDs have greatly varied forward
voltage specifications for each red, green and blue
LED for a given forward current operating condition.
Refer to Figure 2 or the datasheet for a given RGB
LED to be used with the AAT3128. Since the ISRC1
and ISRC2 output current sources are matched with
negligible voltage dependence, RGB LED bright-
ness and color will be matched regardless of specif-
ic LED forward voltage (V
F
) variations.
0.08
R
SET
Value (kΩ)
38.3
46.6
57.6
76.8
115
232
Forward Current (I
F
) (A)
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
1.00
1.50
2.00
2.50
3.00
3.50
4.00
Table 3: R
SET
Programming Values.
If a desired current source output level is not listed
in Table 3, the R
SET
resistor value may be calculat-
ed using the following formula:
R
SET
=
Where:
V
REF
= 1.2V
I
OUT
= Desired output current for ISRC1 and
ISRC2 (ISRC1 = ISRC2
≤
60mA)
(1920 · V
REF
)
I
OUT
Forward Voltage (V
F
) (V)
Figure 2: Typical RGB LED Forward Voltage
vs. Forward Current Characteristics.
3128.2007.09.1.0
9
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