AAT3683 Datasheet, PDF (15/24 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger

The required ballast resistor values can be esti-
mated using the following formula:
R_BALLAST =
(V_IN - V_F(LED))
I_LED
Example:
R_BALLAST =
(5.0V - 2.0V)
2mA
= 1.5kΩ
Note: Red LED forward voltage (V_F) is typically
2.0V @ 2mA.
Protection Circuitry
Programmable Watchdog Timer
The AAT3683 contains a watchdog timing circuit to
shut down charging functions in the event of a defec-
tive battery cell not accepting a charge over a preset
period of time. Typically, a 0.1µF ceramic capacitor
is connected between the CT pin and ground. When
a 0.1µF ceramic capacitor is used, the device will
time out a shutdown condition if the trickle charge
mode exceeds 25 minutes and a combined trickle
charge plus constant current mode of 3 hours.
When the device transitions to the constant voltage
mode, the timing counter is reset and will time out
after an additional 3 hours if the charge current does
not drop to the charge termination level.
The 3683-4 has a battery fault detector, which, when
used in conjunction with a 0.1µF capacitor on the CT
pin, outputs a 1Hz signal with 50% duty cycle at the
STAT1 pin in the event of a timeout while in the trick-
le charge mode.
Mode
Trickle Charge (TC) Time Out
Trickle Charge (TC) + Constant
Current (CC) Mode Time Out
Constant Voltage (VC)
Mode Time Out
Time
25 minutes
3 hours
3 hours
Table 4: Summary for a 0.1µF Ceramic
Capacitor Used for the Timing Capacitor.
AAT3683
1A Linear Li-Ion Battery Charger
The CT pin is driven by a constant current source
and will provide a linear response to increases in the
timing capacitor value. Thus, if the timing capacitor
were to be doubled from the nominal 0.1µF value,
the time-out periods would be doubled.
If the programmable watchdog timer function is not
needed, it can be disabled by terminating the CT
pin to ground. The CT pin should not be left float-
ing or un-terminated, as this will cause errors in the
internal timing control circuit.
The constant current provided to charge the timing
capacitor is very small, and this pin is susceptible to
noise and changes in capacitance value. Therefore,
the timing capacitor should be physically located on
the printed circuit board layout as close as possible
to the CT pin. Since the accuracy of the internal
timer is dominated by the capacitance value, a 10%
tolerance or better ceramic capacitor is recommend-
ed. Ceramic capacitor materials, such as X7R and
X5R types, are a good choice for this application.
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 AAT3683 charge control
will shut down the device until the voltage on the
BAT pin drops below V_OVP. The AAT3683 will
resume normal charging operation after the over-
voltage condition is removed. During an over-volt-
age event, the STAT LEDs (3683-4 only) will report
a system fault.
Over-Temperature Shutdown
The AAT3683 has a thermal protection control cir-
cuit which will shut down charging functions should
the internal die temperature exceed the preset ther-
mal limit threshold. Once the internal die tempera-
ture falls below the thermal limit, normal operation
will resume the previous charging state.
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 dis-
play a system fault. After the system recovers from
a temperature fault, the device will resume charg-
ing operation.
3683.2007.06.1.0
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