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.
demanded by the load. Under short-circuit or other
over-current operating conditions, the output volt-
age will drop and the AAT3200's die temperature
will 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 are typically tight
tolerance and very stable over temperature. Larger
capacitor values are typically composed of X7R,
X5R, Z5U, or Y5V dielectric materials. Large ceram-
ic capacitors, typically greater than 2.2µF, are often
available in the 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 allow 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 considerations section for recom-
mended 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
Consult capacitor vendor data sheets carefully when
selecting capacitors for use with LDO regulators.
The AAT3200 is designed to deliver a continuous
output load current of 150mA for SOT23 or 250mA
for SOT-89 under normal operating conditions. The
limiting characteristic for the maximum output load
safe operating area is essentially package power dis-
sipation 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 discus-
sions will assume the LDO regulator is mounted on a
printed circuit board utilizing the minimum recom-
mended footprint and the printed circuit board is
0.062-inch thick FR4 material with one ounce copper.
Short-Circuit Protection 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's output voltage will
drop to a level necessary to supply the current
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3200.2005.04.1.1
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