AAT3218 Datasheet, PDF (9/18 Pages) List of Unclassifed Manufacturers – 150mA MicroPower™ High Performance LDO

AAT3218
150mA MicroPower™ High Performance LDO
Applications Information
To assure the maximum possible performance is
obtained from the AAT3218, please refer to the fol-
lowing application recommendations.
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 AAT3218 is physically located more
than 3 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
150mA 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 AAT3218 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 AAT3218 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
low noise characteristics of the AAT3218 LDO regu-
lator. The bypass capacitor is not necessary for
operation of the AAT3218. 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 BYP pin 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 and
turn off time. In applications where fast device turn
on time and turn off 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 AAT3218. 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.
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