AAT3239
500mA MicroPower™ LDO
Functional Block Diagram
IN
Active
Feedback
Control
Over-Current
Protection
OUT
Over-
Temperature
Protection
+
Error
Amplifier
-
EN
Fast
Start
Control
Voltage
Reference
BYP
GND
Functional Description
The AAT3239 is intended for LDO regulator appli-
cations where output current load requirements
range from no load to 500mA. Refer to the Thermal
Considerations discussion of this datasheet for
details on maximum power dissipation.
The advanced circuit design of the AAT3239 has
been specifically optimized for very fast start-up
and shutdown timing. This CMOS LDO has been
tailored for superior transient response characteris-
tics, a trait which is particularly important for appli-
cations that require fast power supply timing, such
as GSM cellular telephone handsets.
The high-speed turn-on capability of the AAT3239
is enabled through the implementation of a fast
start control circuit, which accelerates the power-
up behavior of fundamental control and feedback
circuits within the LDO regulator.
Fast turn-off response time is achieved by an
active output pull-down circuit, which is enabled
when the LDO regulator is placed in shutdown
mode. This active fast shutdown circuit has no
adverse effect on normal device operation.
The AAT3239 has very fast transient response
characteristics, which is an important feature for
8
applications where fast line and load transient
response are required. This rapid transient
response behavior is accomplished through the
implementation of an active error amplifier feedback
control. This proprietary circuit design is unique to
this MicroPower LDO regulator.
The LDO regulator output has been specifically
optimized to function with low-cost, low-ESR
ceramic capacitors. However, the design will allow
for operation over a wide range of capacitor types.
A bypass pin has been provided to allow the addition
of an optional voltage reference bypass capacitor to
reduce output self noise and increase power supply
ripple rejection. Device self noise and PSRR will be
improved by the addition of a small ceramic capaci-
tor in this pin. However, increased values of C
BYPASS
may slow down the LDO regulator turn-on time.
This LDO regulator has complete short-circuit and
thermal protection. The integral combination of
these two internal protection circuits gives the
AAT3239 a comprehensive safety system to guard
against extreme adverse operating conditions.
Device power dissipation is limited to the package
type and thermal dissipation properties. Refer to the
Thermal Considerations discussion of this datasheet
for details on device operation at maximum output
current loads.
3239.2006.03.1.2
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
