PRODUCT DATASHEET
AAT3104178
TM
ChargePump
Low Cost 1x/2x 4 Channel Charge Pump WLED Driver
Input Voltage
2.7V to 5.5V
IN
OUT
COUT
1µF
C+
CIN
1µF
AAT3104
CP
1µF
D1
D2
D3
D4
C-
EN/SET
EN/SET
2
S Cwire
Interface
GND
Figure 4: Higher Current, Single LED Application.
Input Voltage
> VF + VDROP
IN
OUT
COUT
1µF
C+
CIN
1µF
AAT3104
D1
D2
D3
D4
C-
EN/SET
S2Cwire
Interface
EN/SET
GND
Figure 5: Lower Cost 1X Mode Application.
itors larger than 1μF are not typically required for
AAT3104 applications. Capacitor area is another con-
tributor to ESR. Capacitors that are physically large will
have a lower ESR when compared to an equivalent
material smaller capacitor. These larger devices can
improve circuit transient response when compared to an
equal value capacitor in a smaller package size.
Equivalent Series Resistance
ESR is an important characteristic to consider when
selecting a capacitor. ESR is a resistance internal to a
capacitor that is caused by the leads, internal connec-
tions, size or area, material composition, and ambient
temperature. Capacitor ESR is typically measured in mil-
liohms for ceramic capacitors and can range to more
than several ohms for tantalum or aluminum electrolytic
capacitors.
Evaluation Board Layout
When designing a PCB for the AAT3104, the key require-
ments are:
Ceramic Capacitor Materials
1. Place two flying capacitors C1 and C2 as close to the
chip as possible; otherwise 2x mode performance
will be compromised.
2. Place input and output decoupling capacitors as
close to the chip as possible to reduce switching
noise and output ripple.
Ceramic capacitors less than 0.1μF are typically made
from NPO or C0G materials. NPO and C0G materials gen-
erally have tight tolerance and are very stable over tem-
perature. Larger capacitor values are usually composed
of X7R, X5R, Z5U, or Y5V dielectric materials. Large
ceramic capacitors (i.e., larger than 2.2μF) are often
available in low cost Y5V and Z5U dielectrics, but capac-
w w w . a n a l o g i c t e c h . c o m
12
3104.2008.09.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
