AAT3258
300mA LDO Linear Regulator with µP Reset
Functional Block Diagram
OUT
VIN
Over-Current
Protection
Over-
Temperature
Protection
+
Error
Amplifier
Voltage
Reference
-
BYP
SHDN
VDET
MR
+
-
Reset Generator
and Timer
RESET
Oscillator
Voltage
Reference
GND
required. This rapid transient response behavior is
accomplished through the implementation of an
active error amplifier feedback control. This propri-
etary circuit design is unique to this MicroPower
LDO regulator.
Functional Description
The AAT3258 is intended for LDO regulator applica-
tions where output current load requirements range
from no load to 300mA.
The LDO regulator output has been specifically opti-
mized to function with low-cost, low-ESR ceramic
capacitors; however, the design will allow for opera-
tion over a wide range of capacitor types.
The advanced circuit design of the AAT3258 has
been specifically optimized for very fast start-up and
shutdown timing. This proprietary CMOS LDO has
also been tailored for superior transient response
characteristics. These traits are particularly impor-
tant for applications that require fast power supply
timing, such as GSM cellular telephone handsets.
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 CBYPASS
may slow down the LDO regulator turn-on time.
The high-speed turn-on capability is enabled
through the implementation of a fast start control cir-
cuit, which accelerates the power-up behavior of
fundamental control and feedback circuits within the
LDO regulator.
This LDO regulator has complete short-circuit and
thermal protection. The integral combination of
these two internal protection circuits gives the
AAT3258 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 section of this datasheet for
details on device operation at maximum output cur-
rent loads.
Fast turn-off response time is achieved by an active
output pull-down circuit, which is enabled when the
LDO regulator is placed in the shutdown mode. This
active fast shutdown circuit has no adverse effect on
normal device operation.
The AAT3258 has very fast transient response char-
acteristics, which is an important feature for applica-
tions where fast line and load transient response is
10
3258.2006.03.1.6
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
