AAT3237B Advanced Analogic Technologies, Inc., AAT3237B Datasheet - Page 9

• Manufacturer Part Number: AAT3237B
• Description: 300ma Micropower? Ldo Linear Regulator With Power-ok
• Manufacturer: Advanced Analogic Technologies, Inc.

Applications Information
To assure the maximum possible performance is
obtained from the AAT3237B, please refer to the
following application recommendations.
Input Capacitor
Typically, a 1µF or larger capacitor is recommend-
ed for C
not required for basic LDO regulator operation.
However, if the AAT3237B is physically located
more than three centimeters from an input power
source, a C
operation. C
device V
greater than 1µF will offer superior input line tran-
sient response and will assist in maximizing the
highest possible power supply ripple rejection.
Ceramic, tantalum, or aluminum electrolytic capac-
itors may be selected for C
capacitor ESR requirement for C
300mA LDO regulator output operation, ceramic
capacitors are recommended for C
inherent capability over tantalum capacitors to
withstand input current surges from low impedance
sources such as batteries in portable devices.
Output Capacitor
For proper load voltage regulation and operational
stability, a capacitor is required between pins V
and GND.
the LDO regulator ground pin should be made as
direct as practically possible for maximum device
performance.
The AAT3237B 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 output
current conditions range from 1µF to 10µF.
Applications utilizing the exceptionally low output
noise and optimum power supply ripple rejection
characteristics of the AAT3237B should use 2.2µF
or greater for C
increased without limit.
In low output current applications where output
load is less than 10mA, the minimum value for
C
3237B.2006.01.1.3
OUT
can be as low as 0.47µF.
IN
IN
in most applications. A C
pin as practically possible. C
IN
IN
The C
capacitor will be needed for stable
should be located as closely to the
OUT
.
OUT
If desired, C
capacitor connection to
IN
. There is no specific
IN
. However, for
IN
IN
OUT
due to their
capacitor is
IN
may be
values
OUT
LDO Linear Regulator with Power-OK
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3237B.
many advantages over their tantalum and alu-
minum electrolytic counterparts. A ceramic capac-
itor typically has very low ESR, is lower cost, has a
smaller PCB footprint, and is non-polarized. Line
and load transient 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.
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.
Typically, capacitor ESR is measured in milliohms
for ceramic capacitors and can range to more than
several ohms for tantalum or aluminum electrolytic
capacitors.
Ceramic Capacitor Materials: Ceramic capaci-
tors less than 0.1µF are typically made from NPO
or C0G materials. NPO and C0G materials gener-
ally have tight tolerance and are very stable over
temperature. Larger capacitor values are usually
composed of X7R, X5R, Z5U, or Y5V dielectric
materials. These two material types are not recom-
mended 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.
dielectric is better than ±15%.
Capacitor area is another contributor to ESR.
Capacitors that are physically large in size will have
a lower ESR when compared to a smaller sized
capacitor of an equivalent material and capaci-
tance value. These larger devices can improve cir-
cuit transient response when compared to an equal
value capacitor in a smaller package size.
Consult capacitor vendor datasheets carefully
when selecting capacitors for LDO regulators.
The temperature tolerance of X7R
300mA MicroPower™
Ceramic capacitors offer
AAT3237B
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