AAT3242
300mA/150mA Dual CMOS LDO Linear Regulator
greater for COUT. If desired, COUT may be increased
without limit. In low output current applications
where output load is less than 10mA, the minimum
Applications Information
To assure the maximum possible performance is
obtained from the AAT3242, please refer to the fol-
lowing application recommendations.
value for COUT can be as low as 0.47µF.
Capacitor Characteristics
Input Capacitor
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3242. 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.
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 AAT3242 is physically located more than
three centimeters from an input power source, a
CIN capacitor will be needed for stable operation.
CIN should be located as closely to the device VIN
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
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.
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 tem-
perature. 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
For proper load voltage regulation and operational
stability, a capacitor is required between pins VOUT
and GND. The COUT capacitor connection to the
LDO regulator ground pin should be made as direct
as practically possible for maximum device per-
formance. The AAT3242 has been specifically
designed to function with very low ESR ceramic
capacitors. For best performance, ceramic capaci-
tors are recommended.
Ceramic Capacitor Materials
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
±50% 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
Typical output capacitor values for maximum out-
put current conditions range from 1µF to 10µF.
Applications utilizing the exceptionally low output
noise and optimum power supply ripple rejection
characteristics of the AAT3242 should use 2.2µF or
10
3242.2006.04.1.10
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
