AAT3215
150mA CMOS High Performance LDO
In low output current applications where output
load is less then 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 AAT3215, please refer to the fol-
lowing application recommendations.
Bypass Capacitor and Low Noise
Applications
Input Capacitor
A bypass capacitor pin is provided to enhance the
very low noise characteristics of the AAT3215 LDO
regulator. The bypass capacitor is not necessary
for operation of the AAT3215. 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
CBYP may range from 470pF to 10nF. For lowest
noise and best possible power supply ripple rejec-
tion performance a 10nF capacitor should be used.
To practically realize the highest power supply rip-
ple rejection and lowest output noise performance,
it is critical that the capacitor connection between
the BYP pin and GND pin be direct and PCB traces
should be as short as possible. Refer to the PCB
Layout Recommendations section of this docu-
ment for examples.
Typically a 1µF or larger capacitor is recommend-
ed for CIN in most applications. A CIN capacitor is
not required for basic LDO regulator operation.
However, if the AAT3215 is physically located more
than 3 centimeters from an input power source, a
CIN capacitor will be needed for stable operation.
CIN should be located as close 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.
Ceramic, tantalum or aluminum electrolytic capaci-
tors may be selected for CIN. There is no specific
capacitor ESR requirement for CIN. However, for
150mA 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.
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 CBYP should be reduced.
Output Capacitor
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.
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
performance.
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.
The AAT3215 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
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3215. 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.
capacitors.
However, 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 AAT3215 should use 2.2µF or
greater for COUT. If desired, COUT may be increased
without limit.
8
3215.2002.03.0.91
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
