AAT3244
300mA Adjustable Dual CMOS
Low Voltage LDO Linear Regulator
cations where output load is less than 10mA, the
minimum value for COUT can be as low as 0.47µF.
Applications Information
To assure the maximum possible performance is
obtained from the AAT3244, please refer to the fol-
lowing application recommendations.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3244. Ceramic capacitors offer many
advantages over their tantalum and aluminum elec-
trolytic counterparts. A ceramic capacitor typically
has very low ESR, is lower cost, has a smaller PCB
footprint, and is non-polarized. Line and load tran-
sient response of the LDO regulator is improved by
using low ESR ceramic capacitors. Since ceramic
capacitors are non-polarized, they are not prone to
incorrect connection damage.
Input Capacitor
A 1µF or larger capacitor is typically recommended
for CIN in most applications. A CIN capacitor is not
required for basic LDO regulator operation; howev-
er, if the AAT3244 is physically located more than
three centimeters from an input power source, a
CIN capacitor will be needed for stable operation.
C
IN should be located as closely to the device sup-
ply pin as practically possible. CIN values greater
than 1µF will offer superior input line transient
response and will assist in maximizing the highest
possible power supply ripple rejection.
Equivalent Series Resistance
ESR is a very important characteristic to consider
when selecting a capacitor. ESR is the internal
series resistance associated with a capacitor that
includes lead resistance, internal connections,
size and area, material composition, and ambient
temperature.
Ceramic, tantalum, or aluminum electrolytic capac-
itors may be selected for CIN. There is no specific
capacitor ESR requirement for CIN; however, for
300mA LDO regulator output operation, ceramic
capacitors are recommended for CIN due to their
inherent capability over tantalum capacitors to with-
stand input current surges from low impedance
sources, such as batteries in portable devices.
Typically, capacitor ESR is measured in milliohms
for ceramic capacitors and can range to more than
several ohms for tantalum or aluminum electrolytic
capacitors.
Output Capacitor
Ceramic Capacitor Materials
For proper load voltage regulation and operational
stability, a capacitor is required between pins OUT
and GND. The COUT capacitor connection to the
LDO regulator ground pin should be made as
direct as practically possible for maximum device
performance.
Ceramic capacitors less than 0.1µF are typically
made from NPO or C0G materials. NPO and C0G
materials generally have tight tolerance and are
very stable over temperature. Larger capacitor val-
ues are usually composed of X7R, X5R, Z5U, or
Y5V dielectric materials. These two material types
are not recommended for use with LDO regulators
since the capacitor tolerance can vary more than
50ꢀ over the operating temperature range of the
device. A 2.2µF Y5V capacitor could be reduced to
1µF over temperature; this could cause problems
for circuit operation. X7R and X5R dielectrics are
much more desirable. The temperature tolerance
of X7R dielectric is better than 15ꢀ. Capacitor
area is another contributor to ESR. Capacitors
The AAT3244 has been specifically designed to func-
tion with very low ESR ceramic capacitors. For best
performance, ceramic capacitors are recommended.
Typical output capacitor values for maximum out-
put current conditions range from 1µF to 10µF.
Applications requiring low output noise and opti-
mum power supply ripple rejection should use
2.2µF or greater for COUT. If desired, COUT may be
increased without limit. In low output current appli-
3244.200708.0.66 (ADVANCED INFORMATION)
9
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