PRODUCT DATASHEET
AAT2557
TM
SystemPower
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 tailored for supe-
rior transient response characteristics. These traits are
particularly important for applications that require fast
power supply timing.
Over-Voltage Protection
When the voltage on the BAT pin exceeds the over-
voltage protection threshold (VOVP = 4.4V) it is defined
as an over-voltage protection event. If this over-voltage
condition occurs, the charger control circuitry will shut
down the device. The charger will resume normal charg-
ing operation after the over-voltage condition is
removed.
The high-speed turn-on capability is enabled through
implementation of a fast-start control circuit which
accelerates the power-up behavior of fundamental con-
trol 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 AAT2557’s battery charger has a thermal protection
circuit which will shut down charging functions when the
internal die temperature exceeds the preset thermal
limit threshold (145°C). Once the internal die tempera-
ture falls below the thermal limit, normal charging
operation will resume. The AAT2557’s LDO also 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 regu-
lator output will remain in a shutdown state until the
internal die temperature falls back to 12°C below the
145°C trip point.
The regulator comes with complete short-circuit and ther-
mal protection. The combination of these two internal
protection circuits gives a comprehensive safety system
to guard against extreme adverse operating conditions.
The regulator features an enable/disable function. The
EN_LDO pin is active high and is compatible with CMOS
logic levels. To assure the LDO regulator will turn on, the
EN_LDO control level must be greater than 1.5V. The
LDO regulator will be disabled when the voltage on the
EN_LDO pin falls below 0.6V. If the enable function is not
needed in a specific application, it may be tied to INLDO
to keep the LDO regulator in a continuously on state.
Short-Circuit Protection
The AAT2557’s LDO contains an internal short-circuit
protection 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 current limited until the short-circuit condition is
removed from the output or until the package power dis-
sipation exceeds the device thermal limit.
Battery Charger 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 control will automatically resume charging in the
appropriate mode for the condition of the battery.
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.
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
