AAT3687
Lithium-Ion/Polymer Battery Charger
voltage is detected on the ADP pin. The precise
charging function of the AAT3687 may be read from
the DATA pin and/or status LEDs. Please refer to
the Battery Charge Status Indication discussion for
further details on data reporting.
Enable / Disable
The AAT3687 provides an enable function to control
the charger IC on and off. The enable (EN) pin is
active high. When pulled to a logic low level, the
AAT3687 will be shut down and forced into the sleep
state. Charging will be halted regardless of the bat-
tery voltage or charging state. When the device is re-
enabled, the charge control circuit will automatically
reset and resume charging functions with the appro-
priate charging mode based on the battery charge
state and measured cell voltage on the BAT pin.
Thermal Loop Control
Due to the integrated nature of the linear charging
control pass device for the adapter input, a special
thermal loop control system has been employed to
maximize charging current under all operating con-
ditions. The thermal management system meas-
ures 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.
Programming Charge Current
The fast charge constant current charge level is
user programmed with a set resistor placed
between the ADPSET pin and ground. The accu-
racy of the fast charge, as well as the precondi-
tioning trickle charge current, is dominated by the
tolerance of the set resistor used. For this reason,
a 1% tolerance metal film resistor is recommended
for the set resistor function.
The initial thermal loop current can be estimated by
the following equation:
ITLOOP = ICC · 0.44
Eq. 1:
Fast charge constant current levels from 50mA to
1.5A can be set by selecting the appropriate resis-
tor value from Table 1.
The thermal loop control re-evaluates the circuit die
temperature in 330ms intervals and adjusts the fast
charge current back up in small steps to the full fast
charge current level or until an equilibrium current
is discovered and maximized for the given ambient
temperature condition. The thermal loop controls
the system charge level; therefore, the AAT3687
will always provide the highest level of constant
current in the fast charge mode possible for any
given ambient temperature condition.
ADP
RSET (kΩ)
ADP
RSET (kΩ)
ICC
ICC
50
N/A
N/A
800
900
10.2
9.09
8.06
7.32
6.65
6.04
5.62
5.36
75
100
200
300
400
500
600
700
84.5
43.2
28.0
21.0
16.9
13.3
11.5
1000
1100
1200
1300
1400
1500
Adapter Input Charge Inhibit and Resume
The AAT3687 has a UVLO and power on reset fea-
ture so that the charger will suspend charging and
shut down if the input supply to the adapter pin
drops below the UVLO threshold. When power is
re-applied to the adapter pin or the UVLO condi-
tions recovers, the system charge control will
assess the state of charge on the battery cell and
will automatically resume charging in the appropri-
ate mode for the condition of the battery.
Table 1: Recommended RSET Values.
12
3687.2006.10.1.7
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
