AAT3685 Datasheet, PDF (16/23 Pages) Advanced Analogic Technologies – Lithium-Ion/Polymer Battery Charger

AAT3685
Lithium-Ion/Polymer Battery Charger
Event Description
Charge Disabled or Low Supply
Charge Enabled Without Battery
Battery Charging
Charge Completed
Fault
STAT1
Off
Flash¹
On
Off
On
Table 2: LED Display Status Conditions.
STAT2
Off
Flash¹
Off
On
On
The LED anodes should be connected to V_ADP/USB.
The LEDs should be biased with as little current as
necessary to create reasonable illumination; there-
fore, a ballast resistor should be placed between
each of the LED cathodes and the STAT1/2 pins.
LED current consumption will add to the over-ther-
mal power budget for the device package, hence it
is recommended to keep the LED drive current to a
minimum. 2mA should be sufficient to drive most
low-cost green, red, or multi-color LEDs. It is not
recommended to exceed 8mA for driving an indi-
vidual status LED.
The required ballast resistor value can be estimat-
ed using the following formulas:
Eq. 2: R_B(STAT1/2) =
(V_APD/USB - V_F(LED))
I_LED(STAT1/2)
Example:
R_B(STAT1) =
(5.0V - 2.0V)
2mA
=
1.5kΩ
Note: Red LED forward voltage (V_F) is typically
2.0V @ 2mA.
Table 2 shows the four status LED display conditions.
Digital Charge Status Reporting
The AAT3685 has a comprehensive digital data
reporting system by use of the DATA pin feature.
This function can provide detailed information
regarding the state of the charging system. The
DATA pin is a bi-directional port which will read
back a series of data pulses when the system
microcontroller asserts a request pulse. This sin-
gle strobe request protocol will invoke one of 14
possible return pulse counts in which the micro-
controller can look up based on the serial report
shown in Table 3.
The DATA pin function is active low and should nor-
mally be pulled high to V_ADP/USB. 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 the value of the pull-up resistor used is too high,
the strobe pulse from the system microcontroller
may exceed the maximum pulse time and the
DATA output control could issue false status
reports. A 1.5kΩ resistor is recommended when
pulling the DATA pin high to 5.0V at the V_USB input.
If the data line is pulled high to a voltage level less
than 5.0V, the pull-up resistor may be calculated
based on a recommended minimum pull-up current
of 3mA. Use the following formula:
Eq. 3: R_PULL-UP ≤
V_PULL-UP
3mA
1. Flashing rate depends on output capacitance.
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3685.2006.10.1.3