AAT3690 Datasheet, PDF (14/20 Pages) Advanced Analogic Technologies – 1.0A USB Port/Adapter Lithium-Ion/Polymer Battery Charger

AAT3690
1.0A USB Port/Adapter
Lithium-Ion/Polymer Battery Charger
Protection Circuitry
Programmable Watchdog Timer
The AAT3690 contains a watchdog timing circuit for
the adapter input charging mode. No watchdog tim-
ing functions are active for the USB input mode.
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 a
shutdown condition if the fast charge mode
exceeds three hours. When the device transitions
to the constant voltage mode, the timing counter is
reset and will time out after three hours and shut
down the charger.
Mode
Fast Charge (CC) Time Out
Constant Voltage (CV) Mode
Time Out
Time
3 hours
3 hours
Summary for a 0.1μF 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 times would be doubled.
If the programmable watchdog timer function is not
needed, it may be disabled by connecting 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 physical-
ly located on the printed circuit board layout as
closely as possible to the CT pin. Since the accu-
racy of the internal timer is dominated by the
capacitance value, 10% tolerance or better ceram-
ic capacitors are recommended. Ceramic capacitor
materials such as X7R and X5R type 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 AAT3690 charge control
will shut down the device until voltage on the BAT
pin drops below the over-voltage protection thresh-
old (V_OVP). The AAT3690 will resume normal charg-
ing operation after the over-voltage condition is
removed. During an over-voltage event, the STAT
LEDs will report a system fault.
Over-Temperature Shutdown
The AAT3690 has a thermal protection control cir-
cuit which will shut down charging functions should
the internal die temperature exceed the preset
thermal limit threshold.
Battery Temperature Fault Monitoring
In the event of a battery over-temperature condi-
tion, the charge control will turn off the internal pass
device. The STAT LEDs will display a system fault.
After the system recovers from a temperature fault,
the device will resume charging operation.
The AAT3690 checks battery temperature before
starting the charge cycle, as well as during all
stages of charging. This is accomplished by moni-
toring the voltage at the TS pin. This system is
intended to use negative temperature coefficient
(NTC) thermistors, which are typically integrated
into the battery package. Most commonly used
NTC thermistors used in battery packs are approx-
imately 10kΩ at room temperature (25°C).
The TS pin has been specifically designed to
source 80μA of current to the thermistor. The volt-
age on the TS pin that results from the resistive
load should stay within a window from 335mV to
2.32V. If the battery becomes too hot during charg-
ing due to an internal fault, the thermistor will heat
up and reduce in value, thus pulling the TS pin volt-
age lower than the T_S1 threshold and the AAT3690
will signal the fault condition.
If the use of the TS pin function is not required by
the system, it can be left open or terminated to
ground using a 10kΩ resistor.
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3690.2007.01.1.2