AAT3238IJS-1.2-T1 View Datasheet(PDF) - Advanced Analogic Technologies
Part Name
Description
MFG CO.
AAT3238IJS-1.2-T1
Advanced Analogic Technologies
'AAT3238IJS-1.2-T1' PDF : 13 Pages View PDF
PowerLinearTM
PRODUCT DATASHEET
AAT3238
300mA MicroPowerTM High Performance LDO Linear Regulator
is measured in milliohms for ceramic capacitors and can
range to more than several ohms for tantalum or alumi-
num electrolytic capacitors.
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 com-
posed of X7R, X5R, Z5U, or Y5V dielectric materials.
These two material types are not recommended 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 prob-
lems for circuit operation. X7R and X5R dielectrics are
much more desirable. The temperature tolerance of X7R
dielectric is better than ±15%.
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 an equiv-
alent material and capacitance value. These larger devic-
es can improve circuit transient response when compared
to an equal value capacitor in a smaller package size.
Consult capacitor vendor datasheets carefully when
selecting capacitors for LDO regulators.
Enable Function
The AAT3238 features an LDO regulator enable/
disable function. This pin (EN) is active high and is com-
patible with CMOS logic. To assure the LDO regulator will
switch on, the EN turn-on control level must be greater
than 1.5V. The LDO regulator will go into the disable
shutdown mode when the voltage 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.
When the LDO regulator is in shutdown mode, an inter-
nal 1.5kΩ resistor is connected between VOUT and GND.
This is intended to discharge COUT when the LDO regula-
tor is disabled. The internal 1.5kΩ has no adverse effect
on device turn-on time.
Short-Circuit Protection
The AAT3238 contains an internal short-circuit protec-
tion circuit that will trigger when the output load current
exceeds the internal threshold limit. Under short-circuit
conditions, the output of the LDO regulator will be cur-
rent limited until the short-circuit condition is removed
from the output or the LDO regulator package power
dissipation exceeds the device thermal limit.
Thermal Protection
The AAT3238 has an internal thermal protection circuit
which will turn on when the device die temperature
exceeds 145°C. The internal thermal protection 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 shut-
down state until the internal die temperature falls back
below the 145°C trip point.
The combination and interaction between the short-cir-
cuit and thermal protection systems allow the LDO regu-
lator to withstand indefinite short-circuit conditions
without sustaining permanent damage.
No-Load Stability
The AAT3238 is designed to maintain output voltage
regulation and stability under operational no-load condi-
tions. This is an important characteristic for applications
where the output current may drop to zero.
Reverse Output-to-Input
Voltage Conditions and Protection
Under normal operating conditions, a parasitic diode
exists between the output and input of the LDO regula-
tor. The input voltage should always remain greater than
the output load voltage, maintaining a reverse bias on
the internal parasitic diode. Conditions where VOUT might
exceed VIN should be avoided since this would forward
bias the internal parasitic diode and allow excessive cur-
rent flow into the VOUT pin, possibly damaging the LDO
regulator.
In applications where there is a possibility of VOUT
exceeding VIN for brief amounts of time during normal
operation, the use of a larger value CIN capacitor is
highly recommended. A larger value of CIN with respect
to COUT will effect a slower CIN decay rate during shut-
down, thus preventing VOUT from exceeding VIN. In appli-
cations where there is a greater danger of VOUT exceed-
ing VIN for extended periods of time, it is recommended
to place a Schottky diode across VIN to VOUT (connecting
the cathode to VIN and anode to VOUT). The Schottky
diode forward voltage should be less than 0.45V.
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