150mA CMOS High Performance LDO
Applications Information
To assure the maximum possible performance is
obtained from the AAT3215, please refer to the fol-
lowing application recommendations.
greater for C
OUT
. If desired, C
OUT
may be increased
without limit.
In low output current applications where output
load is less than 10mA, the minimum value for
C
OUT
can be as low as 0.47µF.
AAT3215
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 AAT3215 is physically located more
than three centimeters from an input power source,
a C
IN
capacitor will be needed for stable operation.
C
IN
should be located as closely 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 capac-
itors 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.
Bypass Capacitor and Low Noise
Applications
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
C
BYP
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.
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 C0G type) or film
capacitor is highly recommended.
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 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
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
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
9
3215.2006.05.1.6
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
