PRODUCT DATASHEET
AAT2550178
SystemPowerTM
Total Power Solution for Portable Applications
drops below the UVLO threshold. When power is re-
applied to the adapter pin or the UVLO condition recov-
ers and ADP > VBAT, the system charge control will assess
the state of charge on the battery cell and will auto-
matically resume charging in the appropriate mode for
the condition of the battery.
Application Information
AC Adapter Power Charging
The adapter constant current charge levels can be pro-
grammed up to 1A. The AAT2550 will operate from the
adapter input over a 4.0V to 5.5V range.
ICH
ADP RSET (kΩ)
The constant current fast charge current for the adapter
input mode is set by the RSET resistor connected between
the ADPSET and ground. Refer to Table 1 for recommend-
ed RSET values for a desired constant current charge level.
The precise charging function in the adapter mode may be
read from the DATA pin and/or status LEDs. Please refer
to the Battery Charge Status Indication discussion in this
datasheet for further details on data reporting.
100
200
300
400
500
600
700
800
900
1000
84.5
43.2
28.0
21.0
16.9
13.3
11.5
10.2
9.09
8.06
Thermal Loop Control
Due to the integrated nature of the linear charging con-
trol pass device, a special thermal loop control system
has been employed to maximize charging current under
all operation conditions. The thermal management sys-
tem measures the internal circuit die temperature and
reduces the fast charge current when the device exceeds
a preset internal temperature control threshold. Once
the thermal loop control becomes active, the fast charge
current is initially reduced by a factor of 0.44.
Table 1: Resistor Values.
Enable / Disable
The AAT2550 provides an enable function to control the
charger IC on and off. The enable (ENBAT) pin is active
high. When pulled to a logic low level, the AAT2550 will
be shut down and forced into the sleep state. Charging
will be halted regardless of the battery voltage or charg-
ing state. When the device is re-enabled, the charge
control circuit will automatically reset and resume charg-
ing functions with the appropriate charging mode based
on the battery charge state and measured cell voltage.
The initial thermal loop current can be estimated by the
following equation:
ITLOOP = ICH · 0.44
The thermal loop control re-evaluates the circuit die tem-
perature every three seconds and adjusts the fast charge
current back up in small steps to the full fast charge cur-
rent level or until an equilibrium current is discovered and
maximized for the given ambient temperature condition.
The thermal loop controls the system charge level; there-
fore, the AAT2550 will always provide the highest level of
constant current possible in the fast charge mode for any
given ambient temperature condition.
Programming Charge Current
The fast charge constant current charge level is pro-
grammed with a resistor placed between the ADPSET pin
and ground. The accuracy of the fast charge, as well as
the preconditioning trickle charge current, is dominated
by the tolerance of the set resistor used. For this reason,
1% tolerance metal film resistors are recommended for
the set resistor function.
Fast charge constant current levels from 100mA to 1A
can be set by selecting the appropriate resistor value
from Table 1. The RSET resistor should be connected
between the ADPSET pin and ground.
Adapter Input Charge Inhibit and Resume
The AAT2550 has an under-voltage lockout and power on
reset feature so that the charger will suspend charging
and shut down if the input supply to the adapter pin
w w w . a n a l o g i c t e c h . c o m
2550.2008.02.1.3
17
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
