AAT3686_08 Datasheet, PDF (16/23 Pages) Advanced Analogic Technologies – USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger

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AAT3686
USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger
charging. This is accomplished by monitoring 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
approximately 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 within 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, 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 indi-
cate simple functions such as no battery charge activity,
battery charging, charge complete, and charge fault. The
AAT3686 also provides 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 displayed
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 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 using the STAT1
pin and a single 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 illumination; 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 pack-
age, 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 recommended to exceed
8mA for driving an individual status LED.
Event Description
Charge Disabled or Low Supply
Charge Enabled Without Battery
Battery Charging
Charge Completed
Fault
STAT1
Off
Flash¹
On
Off
On
STAT2
Off
Flash¹
Off
On
On
Table 3: Status LED Display Conditions.
The required ballast resistor value can be estimated
using the following formulas:
For connection to the adapter supply:
R = ^{VI - V} _B(STAT1/2)
ADP
F(LED)
LED(STAT1/2)
Example:
R_B(STAT1) =
5.5V - 2.0V
2mA
= 1.75kΩ
Note: Red LED forward voltage (V_F) is typically 2.0V @
2mA.
For connection to the USB supply:
R = ^{VI - V} _B(STAT1/2)
USB
F(LED)
LED(STAT1/2)
Example:
R_B(STAT2) =
5.0V - 3.2V
2mA
= 900Ω
Note: Green LED forward voltage (V_F) is typically 3.2V @
2mA.
The four status LED display conditions are described in
Table 3.
1. Flashing rate depends on output capacitance.
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