AAT3236
300mA CMOS High Performance LDO
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 not prone to
incorrect connection damage.
regulator will switch on, the EN turn-on control level
must be greater than 2.0V. The LDO regulator will
go into the disable shutdown mode when the volt-
age on the EN pin falls below 0.6V. If the enable
function is not needed in a specific application, it
may be tied to VIN to keep the LDO regulator in a
continuously on state.
Equivalent Series Resistance: ESR is a very
important characteristic to consider when selecting a
capacitor. ESR is the internal series resistance asso-
ciated with a capacitor that includes lead resistance,
internal connections, size and area, material compo-
sition, and ambient temperature. Typically, capacitor
ESR is measured in milliohms for ceramic capacitors
and can range to more than several ohms for tanta-
lum or aluminum electrolytic capacitors.
When the LDO regulator is in the shutdown mode,
an internal 1.5kΩ resistor is connected between
VOUT and GND. This is intended to discharge COUT
when the LDO regulator is disabled. The internal
1.5kΩ has no adverse effect on device turn-on time.
Short-Circuit Protection
Ceramic Capacitor Materials: Ceramic capaci-
tors less than 0.1µF are typically made from NPO
or C0G materials. NPO and C0G materials gener-
ally have tight tolerance and are very stable over
temperature. Larger capacitor values are usually
composed of X7R, X5R, Z5U, or Y5V dielectric
materials. These two material types are not recom-
mended for use with LDO regulators since the
capacitor tolerance can vary more than ±50% over
the operating temperature range of the device. A
2.2µF Y5V capacitor could be reduced to 1µF over
temperature; this could cause problems for circuit
operation. X7R and X5R dielectrics are much more
desirable. The temperature tolerance of X7R
dielectric is better than ±15%.
The AAT3236 contains an internal short-circuit pro-
tection circuit that will trigger when the output load
current exceeds 750mA. Under short-circuit condi-
tions, the output will be limited to 750mA until the
LDO regulator package power dissipation exceeds
the device thermal limit or the until the short-circuit
condition is removed.
Thermal Protection
The AAT3236 has an internal thermal protection cir-
cuit which will turn on when the device die temper-
ature exceeds 150°C. The internal thermal protec-
tion circuit will actively turn off the LDO regulator
output pass device to prevent the possibility of over-
temperature damage. The LDO regulator output
will remain in a shutdown state until the internal die
temperature falls back below the 150°C trip point.
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 improve circuit tran-
sient response when compared to an equal value
capacitor in a smaller package size.
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.
Consult capacitor vendor datasheets carefully
when selecting capacitors for LDO regulators.
No-Load Stability
The AAT3236 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.
Enable Function
The AAT3236 features an LDO regulator enable /
disable function. This pin (EN) is active high and is
compatible with CMOS logic. To assure the LDO
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3236.2007.03.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
