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Applications Information
Input Capacitor
Typically a 1μF or larger capacitor is recommend-
ed for C
IN
in most applications. A C
IN
capacitor is
not required for basic LDO regulator operation.
However, if the AAT3236 is physically located more
than 6 centimeters from an input power source, a
C
IN
capacitor will be needed for stable operation.
C
IN
should be located as close to the device V
IN
pin
as practically possible. C
IN
values greater than
1μF will offer superior input line transient response
and will assist in maximizing the highest possible
power supply ripple rejection.
Ceramic, tantalum or aluminum electrolytic capaci-
tors may be selected for C
IN
. There is no specific
capacitor ESR requirement for C
IN
. However, for
300mA LDO regulator output operation, ceramic
capacitors are recommended for C
IN
due to their
inherent capability over tantalum capacitors to with-
stand 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
OUT
and GND. The C
OUT
capacitor connection to
the LDO regulator ground pin should be made as
direct as practically possible for maximum device
performance.
The AAT3236 has been specifically designed to
function with very low ESR ceramic capacitors.
Although the device is intended to operate with
these low ESR capacitors, it is stable over a very
wide range of capacitor ESR, thus it will also work
with higher ESR tantalum or aluminum electrolytic
capacitors. However, for best performance,
ceramic capacitors are recommended.
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 AAT3236 should use 2.2μF or
greater for C
OUT
. If desired, C
OUT
may be
increased without limit.
In low output current applications where output
load is less then 10mA, the minimum value for
C
OUT
can be as low as 0.47μF.
Bypass Capacitor and Low Noise
Applications
A bypass capacitor pin is provided to enhance the
very low noise characteristics of the AAT3236 LDO
regulator. The bypass capacitor is not necessary for
operation of the AAT3236. However, for best device
performance, a small ceramic capacitor should be
placed between the Bypass pin (BYP) and the device
ground pin (GND). The value of C
BYP
may range
from 470pF to 10nF. For lowest noise and best pos-
sible power supply ripple rejection performance a
10nF capacitor should be used. To practically realize
the highest power supply ripple rejection and lowest
output noise performance, it is critical that the capac-
itor connection between the BYPpin and GND pin be
direct and PCB traces should be as short as possi-
ble. Refer to the PCB Layout Recommendations
section of this document for examples.
There is a relationship between the bypass capac-
itor value and the LDO regulator turn on time. In
applications where fast device turn on time is
desired, the value of C
BYP
should be reduced.
In applications where low noise performance
and/or ripple rejection are less of a concern, the
bypass capacitor may be omitted. The fastest
device turn on time will be realized when no bypass
capacitor is used.
DC leakage on this pin can affect the LDO regula-
tor output noise and voltage regulation perform-
ance. For this reason, the use of a low leakage,
high quality ceramic (NPO or COG type) or film
capacitor is highly recommended.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3236. 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.
Equivalent Series Resistance (ESR):
ESR is a very
important characteristic to consider when selecting a
capacitor. ESR is the internal series resistance asso-
AAT3236
300mA CMOS High Performance LDO
8
3236.2001.11.0.9