PRODUCT DATASHEET
AAT3103
ChargePumpTM
3-Channel Charge-Pump LED Driver
performance will be obtained when low equivalent series
resistance (ESR) ceramic capacitors are used; in general,
low ESR may be defined as less than 100mΩ. A value of
1μF for all three capacitors is a good starting point when
choosing capacitors.
Additional Applications
The current sources of the AAT3103 can be combined to
drive higher current levels through a single LED. As an
example, a single LED can be driven at 60mA total by
combining together the D1-D3 outputs as shown in
Figure 6.
Capacitor Characteristics
For lower-cost applications, the flying capacitor can be
removed. This will force the AAT3103 to operate in 1x
mode. To maintain regulated LED current, the input supply
voltage must be greater than the charge pump’s dropout
voltage and the current source voltage drop in 1x mode.
For example, to power 3.0V VF with 20mA LED current, VIN
should be greater than 4.0V as shown in Figure 7.
Ceramic composition capacitors are highly recommended
over all other types of capacitors for use with the AAT3103.
Ceramic capacitors offer many advantages over their tan-
talum and aluminum electrolytic counterparts. 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 to maximize charge pump tran-
sient response. Since ceramic capacitors are non-polar-
ized, they are not prone to incorrect connection damage.
Capacitor Selection
Careful selection of the three external capacitors CIN, CP,
and COUT is important because they will affect turn-on
time, output ripple, and transient performance. Optimum
D1
U1
C2
1μF
AAT3103
1
2
3
4
5
10
D1
OUT
C-
C+
IN
D2
D3
AGND
RSET
9
C1
1μF
8
7
6
VIN
EN/SET
R1
14.3k
C3
1μF
EN/SET
Figure 6: Higher Current, Single LED Application.
U1
AAT3103
C2
1μF
1
2
3
4
5
10
9
D1
OUT
C-
C+
IN
D2
D3
AGND
RSET
EN/SET
8
D3
D2
D1
7
6
VIN
R1
14.3k
C3
1μF
EN/SET
Figure 7: Lower Cost 1x Mode Application.
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3103.2008.03.1.0
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
