AAT3215
150mA CMOS High Performance LDO
greater for COUT. If desired, COUT may be increased
without limit.
Applications Information
To assure the maximum possible performance is
obtained from the AAT3215, please refer to the fol-
lowing application recommendations.
In low output current applications where output
load is less than 10mA, the minimum value for
COUT can be as low as 0.47µF.
Input Capacitor
Bypass Capacitor and Low Noise
Applications
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 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.
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 sup-
ply ripple rejection and lowest output noise per-
formance, 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 document for examples.
Ceramic, tantalum, or aluminum electrolytic capac-
itors 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
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.
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.
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
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 C0G type) or film
capacitor is highly recommended.
capacitors.
ceramic capacitors are recommended.
However, for best performance,
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
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
3215.2006.05.1.6
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
