AAT3687_08 Datasheet, PDF (14/20 Pages) Advanced Analogic Technologies – Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
current, the thermistor will heat up and reduce in value,
pulling the TS pin voltage lower than the TS1 threshold,
and the AAT3687 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 AAT3687-1 and AAT3687-2,
the TS pin may be left open.
Battery Charge Status Indication
The AAT3687 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 AAT3687 also provides a bi-directional data reporting
function so that a system microcontroller can interrogate
the DATA pin and read any one of 12 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 AAT3687. These two pins are simple
open drain switches used 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 V_ADP.
The LEDs should be biased with as little current as nec-
essary to create reasonable illumination; therefore, a
ballast resistor should be placed between the LED cath-
odes and the STAT1/2 pins. LED current consumption
will add to the overall thermal power budget for the
device package, hence it is good 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 recommend-
ed to exceed 8mA for driving an individual status LED.
The required ballast resistor values can be estimated
using the following formulas:
Eq. 2: R_B(STAT1/2) =
(V_ADP - V_F(LED))
I_LED(STAT1/2)
PRODUCT DATASHEET
AAT3687
Lithium-Ion/Polymer Battery Charger
Example:
Eq. 3: R_B(STAT1) =
(5.5V - 2.0V)
2mA
=
1.75kΩ
Note: Red LED forward voltage (V_F) is typically 2.0V @
2mA
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: LED Status Indicator.
Digital Charge Status Reporting
The AAT3687 has a comprehensive digital data reporting
system by use of the DATA pin feature. This function can
provide detailed information regarding the status of the
charging system. The DATA pin is a bi-directional port
which will read back a series of data pulses when the sys-
tem microcontroller asserts a request pulse. This single
strobe request protocol will invoke one of 12 possible
return pulse counts that the system microcontroller can
look up based on the serial report data listed in Table 4.
N
DATA Report Status
1
Chip Over-Temperature Shutdown.
2
Battery Temperature Fault.
3
Over-Voltage Turn Off.
4
Not Used.
5
ADP Watchdog Time-Out in Battery Condition Mode.
6
ADP Battery Condition Mode.
7
ADP Watchdog Time-Out in Constant Current Mode.
8 ADP Thermal Loop Regulation in Constant Current Mode.
9
ADP Constant Current Mode.
10 ADP Watchdog Time-Out in Constant Voltage Mode.
11
ADP Constant Voltage Mode.
12
ADP End of Charging.
23
Data Report Error.
Table 4: Serial Data Report Table.
1. Flashing rate depends on output capacitance.
14
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