AAT3103 Datasheet, PDF (13/17 Pages) Advanced Analog Technology, Inc. – 3-Channel Charge-Pump LED Driver

ChargePump^TM
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.
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 V_F with 20mA LED current, V_IN
should be greater than 4.0V as shown in Figure 7.
Capacitor Selection
Careful selection of the three external capacitors C_IN, C_P,
and C_OUT is important because they will affect turn-on
time, output ripple, and transient performance. Optimum
PRODUCT DATASHEET
AAT3103
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.
Capacitor Characteristics
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.
C2
1μF
C1
1μF
VIN
C3
1μF
U1
AAT3103
1 _D1
2
OUT
3
C-
4 _C+
5
IN
D2 ¹⁰
9
D3
8
AGND
RSET ⁷
6
EN/SET
EN/SET
D1
R1
14.3k
Figure 6: Higher Current, Single LED Application.
C2
1μF
VIN
C3
1μF
U1
1
AAT3103
D1
2 _OUT
3 _C-
4
C+
5 _IN
D2 ¹⁰
D3 ⁹
AGND ⁸
7
RSET
EN/SET ⁶
EN/SET
R1
14.3k
D3 D2 D1
Figure 7: Lower Cost 1x Mode Application.
3103.2008.03.1.0
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