AAT3683_08 Datasheet, PDF (15/23 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger

BatteryManager^TM
The required ballast resistor values can be estimated
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 defective bat-
tery 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 trickle 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.
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.
PRODUCT DATASHEET
AAT3683
1A Linear Li-Ion Battery Charger
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 floating or un-
terminated, as this will cause errors in the internal tim-
ing 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 domi-
nated by the capacitance value, a 10% tolerance or bet-
ter ceramic capacitor is recommended. Ceramic capaci-
tor 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 maximum bat-
tery charge voltage and is set by the over-voltage pro-
tection threshold (V_OVP). If an over-voltage 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-voltage event, the STAT LEDs (3683-4 only) will
report a system fault.
Over-Temperature Shutdown
The AAT3683 has a thermal protection control circuit
which will shut down charging functions should the inter-
nal die temperature exceed the preset thermal limit
threshold. Once the internal die temperature falls below
the thermal limit, normal operation will resume the pre-
vious charging state.
Battery Temperature Fault Monitoring
In the event of a battery over-temperature condition,
the charge control will turn off the internal pass device
and report a battery temperature fault on the STAT pins.
After the system recovers from a temperature fault, the
device will resume charging operation.
The AAT3683-2 checks battery temperature before
starting the charge cycle, as well as during all stages of
charging. This is accomplished by monitoring the voltage
at the TS pin. This system is intended for use with
negative temperature coefficient thermistors (NTC)
which are typically integrated into the battery package.
3683.2007.11.1.2
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