AAT3128_08 ANALOGICTECH [Advanced Analogic Technologies], AAT3128_08 Datasheet - Page 9

• Manufacturer Part Number: AAT3128_08
• Description: RGB LED Fashion Lighting Controller
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

ChargePump
Application Information
R
The maximum output current for current sources ISRC1
and ISRC2 is programmed by the R
nal value of 38.3kΩ will set each current source output
to 60mA each. Lower maximum current levels may be
programmed by reducing the value of R
Table 3 for R
brightness constant current rounded off to the closest
1% value.
If a desired current source output level is not listed in
Table 3, the R
the following formula:
Where:
V
I
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 volt-
age 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.
Figure 2 or the datasheet for a given RGB LED to be used
3128.2008.02.1.1
OUT
REF
SET
Current Source Output (mA)
(ISRC1 = ISRC2 ≤ 60mA)
= 1.2V
= Desired output current for ISRC1 and ISRC2
Selection
Table 3: R
SET
SET
60
50
40
30
20
10
resistor value may be calculated using
TM
resistor values to set the maximum
R
SET
SET
=
Programming Values.
(1920 · V
I
OUT
REF
SET
)
R
resistor. A nomi-
SET
SET
Value (kΩ)
38.3
46.6
57.6
76.8
115
232
.
w w w . a n a l o g i c t e c h . c o m
Refer to
Refer to
with the AAT3128. Since the ISRC1 and ISRC2 output
current sources are matched with negligible voltage
dependence, RGB LED brightness and color will be
matched regardless of specific LED forward voltage (V
variations.
Capacitor Selection
Careful selection of the four external capacitors C
C2, and C
on time, output ripple, and transient performance.
Optimum performance will be obtained when low equiv-
alent series resistance (ESR) ceramic capacitors are
used. In general, low ESR may be defined as less than
50mΩ. For best overall performance, 1μF capacitors are
recommended.
Depending on ripple requirements, the input and output
capacitor values can be increased or decreased accord-
ingly. If lower ripple is desired, increase the capacitor
value. The peak-to-peak ripple seen at the input or out-
put increases or decreases with capacitor size.
Capacitor Characteristics
Ceramic composition capacitors are highly recommend-
ed over all other types of capacitors for use with the
AAT3128. Ceramic capacitors offer many advantages
over their tantalum and aluminum electrolytic counter-
parts. A ceramic capacitor typically has very low ESR, is
lowest cost, has a smaller PCB footprint, and is non-
polarized. Low ESR ceramic capacitors help maximize
charge pump transient response. Since ceramic capaci-
tors are non-polarized, they are not prone to incorrect
connection damage.
Figure 2: Typical RGB LED Forward Voltage vs.
RGB LED Fashion Lighting Controller
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
1.00
Forward Current Characteristics.
OUT
is important because they will affect turn-
1.50
Forward Voltage (V
PRODUCT DATASHEET
2.00
2.50
AAT3128
3.00
F
) (V)
3.50
IN
4.00
, C1,
F
9
)