AAT2557
500mA Battery Charger and 300mA
LDO Regulator for Portable Systems
Linear Regulator
Protection Circuitry
The advanced circuit design of the linear regulator
has been specifically optimized for very fast start-
up. This proprietary CMOS LDO has also been tai-
lored for superior transient response characteris-
tics. These traits are particularly important for appli-
cations that require fast power supply timing.
Over-Voltage Protection
A battery charger over-voltage protection event is
defined as a condition where the voltage on the
BAT pin exceeds the over-voltage protection
threshold (VOVP) (4.4V). If this over-voltage condi-
tion occurs, the charger control circuitry will shut
down the device. The charger will resume normal
charging operation after the over-voltage condition
is removed.
The high-speed turn-on capability is enabled
through implementation of a fast-start control cir-
cuit which accelerates the power-up behavior of
fundamental control and feedback circuits within
the 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.
Over-Temperature Protection
The battery charger has a thermal protection circuit
which will shut down charging functions when the
internal die temperature exceeds the preset ther-
mal limit threshold (145°C). Once the internal die
temperature falls below the thermal limit, normal
charging operation will resume.
The regulator comes with complete short-circuit
and thermal protection. The combination of these
two internal protection circuits gives a comprehen-
sive safety system to guard against extreme
adverse operating conditions.
Short-Circuit Protection
The AAT2557’s LDO contains an internal short-cir-
cuit protection circuit that will trigger when the out-
put load current exceeds the internal threshold
limit. Under short-circuit conditions, the output of
the LDO regulator will be current limited until the
short-circuit condition is removed from the output
or until the package power dissipation exceeds the
device thermal limit.
The regulator features an enable/disable function.
This pin (ENLDO) is active high and is compatible
with CMOS logic. To assure the LDO regulator will
switch on, the ENLDO 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 ENLDO pin falls below 0.6V. If the enable func-
tion is not needed in a specific application, it may
be tied to INLDO to keep the LDO regulator in a
continuously on state.
Thermal Protection
The AAT2557’s LDO has an internal thermal protec-
tion circuit which will turn on when the device die
temperature exceeds 145°C. The internal thermal
protection circuit will actively turn off the LDO regu-
lator output pass device to prevent the possibility of
overtemperature damage. The LDO regulator output
will remain in a shutdown state until the internal die
temperature falls back below the 145°C trip point.
Under-Voltage Lockout
The AAT2557 has internal circuits for UVLO and
power on reset features. If the ADP supply voltage
drops below the UVLO threshold, the battery
charger will suspend charging and shut down.
When power is reapplied to the ADP pin or the
UVLO condition recovers, the system charge con-
trol will automatically resume charging in the
appropriate mode for the condition of the battery.
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.
2557.2007.06.1.0
13
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
