AAT2550
Total Power Solution for Portable Applications
When power is re-applied to the adapter pin or the
UVLO condition recovers and ADP > VBAT, the sys-
tem charge control will assess the state of charge
on the battery cell and will automatically 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
programmed up to 1A. The AAT2550 will operate
from the adapter input over a 4.0V to 5.5V range.
The constant current fast charge current for the
adapter input mode is set by the RSET resistor con-
nected between the ADPSET and ground. Refer to
Table 1 for recommended 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.
ADP
ICH
RSET (kΩ)
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
control pass device, a special thermal loop control
system has been employed to maximize charging
current under all operation conditions. The thermal
management system measures the internal circuit
die temperature and reduces the fast charge cur-
rent when the device exceeds a preset internal
temperature control threshold. Once the thermal
loop control becomes active, the fast charge cur-
rent is initially reduced by a factor of 0.44.
Table 1: Resistor Values.
Enable / Disable
The AAT2550 provides an enable function to con-
trol the charger IC on and off. The enable (EN) 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 charging state. When the
device is re-enabled, the charge control circuit will
automatically reset and resume charging 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
temperature every three seconds and adjusts the
fast charge current back up in small steps to the full
fast charge current level or until an equilibrium cur-
rent is discovered and maximized for the given
ambient temperature condition. The thermal loop
controls the system charge level; therefore, 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
programmed 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.
Adapter Input Charge Inhibit and Resume
The AAT2550 has an under-voltage lockout and
power on reset feature so that the charger will sus-
pend charging and shut down if the input supply to
the adapter pin drops below the UVLO threshold.
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 con-
nected between the ADPSET pin and ground.
2550.2006.07.1.0
17
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