AAT3687_08 Datasheet, PDF (12/20 Pages) Advanced Analogic Technologies – Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
Application Information
Adapter Power Input
Constant current charge levels up to 1.5A may be pro-
grammed by the user when powered from a sufficient
input power source. The AAT3687 will operate from the
adapter input over a 4.0V to 5.5V range.
The constant current fast charge current for the adapter
input is set by the R_SET resistor connected between the
ADPSET and ground. Refer to Table 1 for recommended
R_SET values for a desired constant current charge level.
The presence of voltage on the adapter input is indicated
by the ADPP# pin function. This indicator pin uses an
internal open drain device that will pull the ADPP# pin
low when voltage is detected on the ADP pin. The pre-
cise 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.
Thermal Loop Control
Due to the integrated nature of the linear charging con-
trol pass device for the adapter input, a special thermal
loop control system has been employed to maximize
charging current under all operating conditions. The
thermal management system measures the internal cir-
cuit 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.
The initial thermal loop current can be estimated by the
following equation:
Eq. 1: I_TLOOP = I_CC · 0.44
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 tem-
perature condition. The thermal loop controls the sys-
tem charge level; therefore, the AAT3687 will always
provide the highest level of constant current in the fast
charge mode possible for any given ambient tempera-
ture condition.
PRODUCT DATASHEET
AAT3687
Lithium-Ion/Polymer Battery Charger
Adapter Input Charge Inhibit and Resume
The AAT3687 has a UVLO and power on reset feature 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 adapt-
er pin or the UVLO conditions recovers, the system
charge control will assess the state of charge on the bat-
tery cell and will automatically resume charging in the
appropriate mode for the condition of the battery.
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 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
on the BAT pin.
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 accuracy of the fast
charge, as well as the preconditioning trickle charge cur-
rent, 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.
Fast charge constant current levels from 50mA to 1.5A
can be set by selecting the appropriate resistor value
from Table 1.
ADP
ADP
I_CC
R_SET (kΩ)
I_CC
R_SET (kΩ)
50
N/A
800
10.2
75
N/A
900
9.09
100
84.5
1000
8.06
200
43.2
1100
7.32
300
28.0
1200
6.65
400
21.0
1300
6.04
500
16.9
1400
5.62
600
13.3
1500
5.36
700
11.5
Table 1: Recommended R_SET Values.
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3687.2008.04.1.12