AAT3200
OmniPower™ LDO Linear Regulator
resistance, internal connections, capacitor size and
area, material composition, and ambient tempera-
ture. Typically, capacitor ESR is measured in mil-
liohms for ceramic capacitors and can range to
more than several ohms for tantalum or aluminum
electrolytic capacitors.
over-current operating conditions, the output volt-
age would drop and the AAT3200 die temperature
would increase rapidly. Once the regulator's power
dissipation capacity has been exceeded and the
internal die temperature reaches approximately
140°C, the system thermal protection circuit will
become active. The internal thermal protection cir-
cuit will actively turn off the LDO regulator output
pass device to prevent the possibility of over-tem-
perature damage. The LDO regulator output will
remain in a shutdown state until the internal die
temperature falls back below the 140°C trip point.
Ceramic Capacitor Materials: Ceramic capacitors
less than 0.1µF are typically made from NPO or C0G
materials. NPO and C0G materials generally have
tight tolerance and are very stable over temperature.
Larger capacitor values are usually composed of
X7R, X5R, Z5U, or Y5V dielectric materials. Large
ceramic capacitors (i.e., greater than 2.2µF) are
often available in low-cost Y5V and Z5U dielectrics.
These two material types are not recommended for
use with LDO regulators since the capacitor toler-
ance can vary by more than ±50% over the operat-
ing temperature range of the device. A 2.2µF Y5V
capacitor could be reduced to 1µF over the full oper-
ating temperature range. This can cause problems
for circuit operation and stability. X7R and X5R
dielectrics are much more desirable. The tempera-
ture tolerance of X7R dielectric is better than ±15%.
The combination and interaction between the short-
circuit and thermal protection systems allows the
LDO regulator to withstand indefinite short-circuit
conditions without sustaining permanent damage.
No-Load Stability
The AAT3200 is designed to maintain output volt-
age regulation and stability under operational no-
load conditions. This is an important characteristic
for applications where the output current may drop
to zero. An output capacitor is required for stability
under no-load operating conditions. Refer to the
Output Capacitor section of this datasheet for rec-
ommended typical output capacitor values.
Capacitor area is another contributor to ESR.
Capacitors that are physically large in size will have
a lower ESR when compared to a smaller sized
capacitor of equivalent material and capacitance
value. These larger devices can also improve cir-
cuit transient response when compared to an equal
value capacitor in a smaller package size.
Thermal Considerations and High
Output Current Applications
The AAT3200 is designed to deliver a continuous
output load current of 150mA for an SC59 package
or 250mA for a SOT-89 package under normal
operating conditions. The limiting characteristic for
the maximum output load safe operating area is
essentially package power dissipation and the
internal preset thermal limit of the device. In order
to obtain high operating currents, careful device
layout and circuit operating conditions need to be
taken into account. The following discussions will
assume the LDO regulator is mounted on a printed
circuit board utilizing the minimum recommended
footprint and the printed circuit board is 0.062-inch
thick FR4 material with one ounce copper.
Consult capacitor vendor datasheets carefully when
selecting capacitors for use with LDO regulators.
Short-Circuit and Thermal Protection
The AAT3200 is protected by both current limit and
over-temperature protection circuitry. The internal
short-circuit current limit is designed to activate
when the output load demand exceeds the maxi-
mum rated output. If a short-circuit condition were
to continually draw more than the current limit
threshold, the LDO regulator output voltage would
drop to a level necessary to supply the current
demanded by the load. Under short-circuit or other
10
3200.2006.02.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
