AAT3663 Datasheet, PDF (16/22 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications

AAT3663
1A Linear Li-Ion Battery Charger
for Single and Dual Cell Applications
Protection Circuitry
Programmable Timer Function
The AAT3663 contains a watchdog timing circuit to
shut down charging functions in the event of a
defective 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 ter-
mination level.
The AAT3663 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 (CV) Mode Time Out
Time
25 minutes
3 hours
3 hours
Table 3: 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 timeout 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 floating
or unterminated, 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 print-
ed 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% toler-
ance or better ceramic capacitor is recommended.
16
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 AAT3663 charge control
will shut down the device until the voltage on the
BAT pin drops below V_OVP. The AAT3663 will
resume normal charging operation after the over-
voltage condition is removed. During an over-volt-
age event, the STAT LEDs will report a system fault.
Over-Temperature Shutdown
The AAT3663 has a thermal protection control cir-
cuit which will shut down charging functions once
the internal die temperature exceeds the over-tem-
perature shutdown threshold. Once the internal die
temperature falls below the hysteresis, normal
operation will resume the previous charging state.
Battery Temperature Fault Monitoring
There are two AAT3663 temperature sense options,
The AAT3663-1 and AAT3663-2. The AAT3663-1
option allows of the use of any NTC resistor. For
ease of use, the AAT3663-2 option is factory set to
function with typical 10kΩ NTC resistors and elimi-
nates the need for a resistor divider pull up to the
input power source.
Regardless of the AAT3663 option selected, the
internal system control checks battery temperature
before starting the charge cycle and continues to
monitor the battery temperature during all stages of
the charging cycle. This is accomplished by moni-
toring the voltage at the TS pin. In general, the sys-
tem is intended for use with negative temperature
coefficient thermistors (NTC) which are typically
integrated into the battery package. The voltage on
the TS pin resulting from the resistive load and
applied current, should stay within a window
bounded by the TS1 and TS2 specification thresh-
olds. Refer to the Electrical Characteristics table
for the TS1 and TS2 limits for a selected AAT3663
option. If the battery becomes too hot during
charge cycle due to an internal fault or excessive
charge current, the NTC thermistor will heat up and
reduce in value. This in turn will pull the TS pin
3663.2007.10.1.0