AAT3663_08 Datasheet, PDF (18/23 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications

BatteryManager^TM
PRODUCT DATASHEET
AAT3663
1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications
timer function is not needed, it can be disabled by ter-
minating 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 capac-
itance 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 recom-
mended. 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 maximum bat-
tery charge voltage and is set by the overvoltage protec-
tion threshold (V_OVP). If an over-voltage 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 overvoltage condition is removed. During an over-
voltage event, the STAT LEDs will report a system fault.
Over-Temperature Shutdown
The AAT3663 has a thermal protection control circuit
which will shut down charging functions once the internal
die temperature exceeds the over-temperature shut-
down 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 eliminates 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 start-
ing the charge cycle and continues to monitor the bat-
tery temperature during all stages of the charging cycle.
This is accomplished by monitoring the voltage at the TS
pin. In general, the system 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 thresholds.
Refer to the Electrical Characteristics table for the TS1
and TS2 limits for a selected AAT3663 option. If the bat-
tery 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 voltage below than the TS1 threshold,
and indicate a battery cell temperature fault. The charg-
ing process will then be suspended until the over-tem-
perature condition is removed, at which time charging
will resume. Conversely, if the battery under charge is
exposed to extreme cold ambient temperature condition,
the NTC thermistor may increase in value and push the
voltage on the TS pin above the TS2 threshold. In such
a case, the charge cycle will be suspended and will not
resume until the cold fault condition is removed. Both
TS1 and TS2 temperature fault conditions will be report
by the STAT1 and STAT2 LEDs.
AAT3663-1 Option
the AAT3663-1 option utilizes an internal battery tem-
perature sensing system comprised of two comparators
which establish a voltage window for safe operation. The
thresholds for the TS operating window are bounded by
the TS1 and TS2 specifications. Referring to the electri-
cal characteristics table in this datasheet, the TS1
threshold = 0.30 · V_IN and the TS2 threshold = 0.6 · V_IN.
Refer to Figure 4 for external resistor and NTC thermis-
tor connections.
If the use of the battery temperature sense function is
not required, it may be disabled by terminating the TS
pin to IN and ground using a 10kΩ resistor divider net-
work. If circuit power dissipation is a concern, the two
terminating resistor values may be increased to 100kΩ.
AAT3663-2 Option
Most of the commonly used NTC thermistors in Li-Ion/
Polymer battery packs are approximately 10kΩ at room
temperature (25°C). The AAT3663-2 TS pin has been
specifically designed to source 75μA of current to the
10kΩ NTC thermistor. The applied constant current
source and fixed internal TS1 and TS2 voltage thresholds
eliminate the need for a resistor divider on the TS pin.
Simply connect the 10kΩ NTC resistor between the TS
pin and ground. If the TS function is not needed for the
AAT3663-2, it may be left open (not connected).
18
www.analogictech.com
3663.2008.01.1.2