AAT3686 Datasheet, PDF (16/24 Pages) Advanced Analogic Technologies – USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger

AAT3686
USB Port/AC Adapter
Lithium-Ion/Polymer Battery Charger
Over-Voltage Protection
An over-voltage event is defined as a condition
where the voltage on the BAT pin exceeds the max-
imum battery charge voltage and is set by the over-
voltage protection threshold (V_OVP). If an over-volt-
age condition occurs, the AAT3686 charge control
will shut down the device until voltage on the BAT
pin drops below the over-voltage protection thresh-
old (V_OVP). The AAT3686 will resume normal charg-
ing operation after the over-voltage condition is
removed. During an over-voltage event, the STAT
LEDs will report a system fault, and the actual fault
condition may be read via the DATA pin signal.
Over-Temperature Shutdown
The AAT3686 has a thermal protection control cir-
cuit which will shut down charging functions should
the internal die temperature exceed the preset
thermal limit threshold.
Battery Temperature Fault Monitoring
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 display
a system fault. After the system recovers from a
temperature fault, the device will resume charging
operation.
The AAT3686 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 to use negative temperature coefficient
thermistors (NTC), which are typically integrated
into the battery package. Most of the commonly
used NTC thermistors in battery packs are approx-
imately 10kΩ at room temperature (25°C).
The TS pin has been specifically designed to
source 80µA of current to the thermistor. The volt-
age on the TS pin that results from the resistive
load should stay within a window from 335mV to
2.32V. If the battery becomes too hot during charg-
ing due to an internal fault, the thermistor will heat
up and reduce in value, pulling the TS pin voltage
lower than the TS1 threshold and the AAT3686 will
signal the fault condition.
If the use of the TS pin function is not required by
the system, it should be terminated to ground using
a 10kΩ resistor. Alternatively, on the AAT3686-1,
the TS pin may be left open.
Battery Charge Status Indication
The AAT3686 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 AAT3686 also pro-
vides a bi-directional data reporting function so that
a system microcontroller can interrogate the DATA
pin and read any one of 22 system states.
Status Indicator Display
Simple system charging status states can be dis-
played using one or two LEDs in conjunction with the
STAT1 and STAT2 pins on the AAT3686. These two
pins are simple switches to connect the LED cath-
odes to ground. It is not necessary to use both dis-
play LEDs if a user simply wants to have a single
lamp to show "charging" or "not charging." This can
be accomplished by using the STAT1 pin and a sin-
gle LED. Using two LEDs and both STAT pins simply
gives the user more information to the charging
states. Refer to Table 3 for LED display definitions.
The LED anodes should be connected to either
V_USB or V_ADP, depending upon system design
requirements. The LEDs should be biased with as
little current as necessary to create reasonable illu-
mination; therefore, a ballast resistor should be
placed between the LED cathodes and the
STAT1/2 pins. LED current consumption will add to
the overall thermal power budget for the device
package, so it is wise to keep the LED drive current
to a minimum. 2mA should be sufficient to drive
most low-cost green or red LEDs. It is not recom-
mended to exceed 8mA for driving an individual
status LED.
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