AAT3686
USB Port/AC Adapter
Lithium-Ion/Polymer Battery Charger
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 3: Status LED Display Conditions.
The required ballast resistor value can be estimat-
ed using the following formulas:
Digital Charge Status Reporting
The AAT3686 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 system microcon-
troller asserts a request pulse. This single strobe
request protocol will invoke one of 22 possible return
pulse counts which the microcontroller can look up
based on the serial report table shown in Table 4.
For connection to the adapter supply:
VADP - VF(LED)
ILED(STAT1/2)
RB(STAT1/2)
=
Example:
RB(STAT1)
5.5V - 2.0V
2mA
=
= 1.75kΩ
The DATA pin function is active low and should nor-
mally be pulled high to VADP or VUSB. This data line
may also be pulled high to the same level as the
high state for the logic I/O port on the system
microcontroller. In order for the DATA pin control
circuit to generate clean, sharp edges for the data
output and to maintain the integrity of the data tim-
ing for the system, the pull-up resistor on the data
line should be low enough in value so that the
DATA signal returns to the high state without delay.
If too small a pull-up resistor is used, the strobe
pulse from the system microcontroller could
exceed the maximum pulse time and the DATA out-
put control could issue false status reports. A 1.5kΩ
resistor is recommended when pulling the DATA
pin high to 5.0V on either VADP or VUSB inputs. If the
data line is pulled high to a voltage level less than
5.0V, the pull-up resistor can be calculated based
on a recommended minimum pull-up current of
3mA. Use the following formula:
Note: Red LED forward voltage (VF) is typically
2.0V @ 2mA.
For connection to the USB supply:
VUSB - VF(LED)
ILED(STAT1/2)
RB(STAT1/2)
=
Example:
5.0V - 3.2V
= 900Ω
2mA
RB(STAT2)
=
Note: Green LED forward voltage (VF) is typically
3.2V @ 2mA.
The four status LED display conditions are
described in Table 3.
VPULL-UP
3mA
RPULL-UP
≤
1. Flashing rate depends on output capacitance.
3686.2006.10.1.9
17
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
