AAT3220
150mA NanoPower™ LDO Linear Regulator
If large output current steps are required by an
application, then an increased value for COUT
should be considered. The amount of capacitance
needed can be calculated from the step size of the
change in the output load current expected and the
voltage excursion that the load can tolerate.
Applications Information
To assure the maximum possible performance is
obtained from the AAT3220, please refer to the fol-
lowing application recommendations.
The total output capacitance required can be cal-
culated using the following formula:
Input Capacitor
Typically, a 1µF or larger capacitor is recommended
for CIN in most applications. A CIN capacitor is not
required for basic LDO regulator operation.
However, if the AAT3220 is physically located any
distance more than one or two centimeters from the
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 val-
ues greater than 1µF will offer superior input line
transient response and will assist in maximizing the
highest possible power supply ripple rejection.
∆I
∆V
COUT
=
× 15µF
Where:
∆I = maximum step in output current
∆V = maximum excursion in voltage that the load
can tolerate.
Note that use of this equation results in capacitor
values approximately two to four times the typical
value needed for an AAT3220 at room temperature.
The increased capacitor value is recommended if
tight output tolerances must be maintained over
extreme operating conditions and maximum opera-
tional temperature excursions. If tantalum or alu-
minum electrolytic capacitors are used, the capaci-
tor value should be increased to compensate for the
substantial ESR inherent to these capacitor types.
Ceramic, tantalum, or aluminum electrolytic capac-
itors may be selected for CIN. There is no specific
capacitor ESR requirement for CIN. For 150mA
LDO regulator output operation, ceramic capacitors
are recommended for CIN due to their inherent
capability over tantalum capacitors to withstand
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 VOUT
and GND. The COUT capacitor connection to the
LDO regulator ground pin should be as direct as
practically possible for maximum device perform-
ance. The AAT3220 has been specifically designed
to function with very low ESR ceramic capacitors.
Although the device is intended to operate with low
ESR capacitors, it is stable over a very wide range
of capacitor ESR, thus it will also work with some
higher ESR tantalum or aluminum electrolytic
capacitors. However, for best performance, ceram-
ic capacitors are recommended.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3220. 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 less prone
to damage if incorrectly connected.
Equivalent Series Resistance: ESR is a very
important characteristic to consider when selecting
a capacitor. ESR is the internal series resistance
associated with a capacitor that includes lead
The value of COUT typically ranges from 0.47µF to
10µF; however, 1µF is sufficient for most operating
conditions.
3220.2006.01.1.4
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
