AAT3688
USB Port Lithium-Ion/Polymer Battery Charger
Battery Temperature Fault Monitoring
function is not required by the system, it should be
In the event of a battery over-temperature condi-
tion, the charge control will turn off the internal pass
device and report a battery temperature fault on the
DATA pin function. The STAT LEDs will also dis-
play a system fault. After the system recovers
from a temperature fault, the device will resume
charging operation.
terminated to ground using a 10kΩ resistor.
Battery Charge Status Indication
The AAT3688 indicates the status of the battery
under charge with two different systems. First, the
device has two status LED driver outputs. These
two LEDs can indicate simple functions such as no
battery charge activity, battery charging, charge
complete, and charge fault. The AAT3688 also
provides a bi-directional data reporting function so
that a system microcontroller may interrogate the
DATA pin and read any one of 14 system states.
The AAT3688 checks battery temperature before
starting the charge cycle, as well as during all
stages of charging. This is accomplished by moni-
toring the voltage at the TS pin. This system is
intended for use negative temperature coefficient
(NTC) thermistors which are typically integrated into
the battery package. Most commonly used NTC
thermistors used in battery packs are approximate-
ly 10kΩ at room temperature (25°C). The TS pin
has been specifically designed to source 80µA of
current to the thermistor. The voltage on the TS pin
that results from the resistive load should stay with-
in a window from 335mV to 2.32V. If the battery
becomes too hot during charging due to an internal
fault, the thermistor will heat up and reduce in value,
thus pulling the TS pin voltage lower than the TS1
threshold, and the AAT3688 will halt charging and
signal the fault condition. If the use of the TS pin
Status Indicator Display
Simple system charging status may be displayed
using one or two LEDs in conjunction with the
STAT1 and STAT2 pins on the AAT3688. These
two pins are simple switches to connect the display
LED cathodes to ground. It is not necessary to use
both display LEDs if a user simply wants to have a
single lamp to show "charging" or "not charging."
This can be accomplished by just using the STAT1
pin and a single LED. Using two LEDs and both
STAT pins simply gives the user more information
for charging states. Refer to Table 2 for LED dis-
play definitions.
Event Description
STAT1
STAT2
Charge Disabled or Low Supply
Charge Enabled Without Battery
Battery Charging
Off
Flash1
On
Off
Flash1
Off
Charge Completed
Off
On
Fault
On
On
Table 2: LED Display Status Conditions.
1. Flashing rate depends on output capacitance.
3688.2006.10.1.5
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
