AAT3783_12 Datasheet, PDF (15/20 Pages) Skyworks Solutions Inc. – 1-A Linear Li-Ion/Polymer Battery Charger with 28V Over-Voltage Protection

DATA SHEET
AAT3783
1-A Linear Li-Ion/Polymer Battery Charger with 28V Over-Voltage Protection
Charge Termination Current
The charge termination current I_{CH_TERM} can be pro-
grammed by connecting a resistor from TERM to GND:
Where:
I_{CH_TERM}
=
15µA · R_TERM
2V
·
I_{CH_CC}
I_{CH_TERM} = Charge termination current level
I_{CH_CC} = Programmed fast charge constant current level
R_TERM = TERM resistor value
If the TERM pin is left open, the termination current will
set to 10% of the constant charging current as the
default value.
When the charge current drops to the defaulted 10% of
the programmed charge current level or programmed
terminated current in the constant voltage mode, the
device terminates charging and goes into a sleep state.
The charger will remain in this sleep state until the bat-
tery voltage decreases to a level below the battery
recharge voltage threshold (V_RCH).
Consuming very low current in sleep state, the AAT3783
minimizes battery drain when it is not charging. This
feature is particularly useful in applications where the
input supply level may fall below the battery charge or
under-voltage lockout level. In such cases where the
AAT3783 input voltage drops, the device will enter sleep
state and automatically resume charging once the input
supply has recovered from the fault condition.
Protection Circuitry
Programmable Watchdog Timer
The AAT3783 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.
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 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 increase 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 watch-
dog 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 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 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.
Battery 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_BOVP). If an over-voltage condition
occurs, the AAT3783 charge control will shut down the
device until the voltage on the BAT pin drops below V_OVP.
The AAT3783 will resume normal charging operation
after the over-voltage condition is removed.
Battery Temperature Monitoring
In the event of a battery over-temperature condition, the
charge control will turn off the internal pass device. After
the system recovers from a temperature fault, the device
will resume charging operation. The AAT3783 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. Most of the commonly used NTC therm-
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201903B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 27, 2012
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