AAT3200
OmniPower™ LDO Linear Regulator
Applications Information
To assure the maximum possible performance is
obtained from the AAT3200, please refer to the fol-
lowing application recommendations.
If large output current steps are required by an
application, then an increased value for C
OUT
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.
The total output capacitance required can be cal-
culated using the following formula:
∆I
×
15µF
∆V
Input Capacitor
Typically, a 1µF or larger capacitor is recommended
for C
IN
in most applications. A C
IN
capacitor is not
required for basic LDO regulator operation.
However, if the AAT3200 is physically located any
distance more than one or two centimeters from the
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 capaci-
tors may be selected for C
IN
. There is no specific
capacitor equivalent series resistance (ESR)
requirement for C
IN
. For 150mA to 250mA LDO reg-
ulator output operation, ceramic capacitors are rec-
ommended for C
IN
due to their inherent capability
over tantalum capacitors to withstand input current
surges from low impedance sources such as bat-
teries in portable devices.
C
OUT
=
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 AAT3200 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.
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 per-
formance. The AAT3200 has been specifically
designed to function with very low ESR ceramic
capacitors. Although the device is intended to oper-
ate with low ESR capacitors, it is stable over a 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.
The value of C
OUT
typically ranges from 0.47µF to
10µF; however, 1µF is sufficient for most operating
conditions.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3200. 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
3200.2006.02.1.4
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
