AAT3697IWP-4.2-T1 Advanced Analog Technology, Inc., AAT3697IWP-4.2-T1 Datasheet - Page 13

• Manufacturer Part Number: AAT3697IWP-4.2-T1
• Description: 2A Lithium-Ion/Polymer Battery Charger
• Manufacturer: Advanced Analog Technology, Inc.

Protection Circuitry
Programmable Watchdog Timer
The AAT3697 contains a watchdog timing circuit to
shut down charging functions in the event of a defec-
tive 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 fast charge mode of 3 hours. When the
device transitions to the constant voltage mode, the
timing counter is reset and will time out after an addi-
tional 3 hours if the charge current does not drop to
the charge termination level.
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.
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 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
close as possible to the CT pin. Since the accura-
cy of the internal timer is dominated by the capaci-
tance value, a 10% tolerance or better ceramic
capacitor is recommended.
materials, such as X7R and X5R types, are a good
choice for this application.
3697.2007.02.1.1
Mode
Trickle Charge (TC) Time Out
Trickle Charge (TC) +
Fast Charge (CC) Time Out
Constant Voltage (VC) Mode
Time Out
Capacitor Used for the Timing Capacitor.
Table 2: Summary for a 0.1μF Ceramic
Ceramic capacitor
25 minutes
3 hours
3 hours
Time
2A Lithium-Ion/Polymer Battery Charger
Over-Voltage Protection
An over-voltage event is defined as a condition
where the voltage on the BAT pin exceeds the
maximum battery charge voltage and is set by the
over-voltage protection threshold (V
over-voltage condition occurs, the AAT3697 charge
control will shut down the device until the voltage
on the BAT pin drops below V
will resume normal charging operation after the
over-voltage condition is removed. During an over-
voltage event, the STAT LEDs will report a system
fault, and the actual fault condition can be read via
the DATA pin signal.
Over-Temperature Shutdown
The AAT3697 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 and report a battery temperature fault on the
DATA pin function. The STAT LEDs will also dis-
play a system fault. After the system recovers from
a temperature fault, the device will resume charg-
ing operation.
The AAT3697 checks battery temperature before
starting the charge cycle, as well as during all
stages of charging. This is accomplished by mon-
itoring the voltage at the TS pin. Either a negative
temperature coefficient thermistor (NTC) or posi-
tive temperature coefficient thermistor (PTC) can
be used because the AAT3697 checks to see that
the voltage at TS is within a voltage window bound-
ed by V
below for specifying resistors:
R
T1
and R
TS1
Eq. 2:
T2
and V
for use with NTC Thermistor
R
R
T1
T2
TS2
=
=
. Please see the equations
3 ⋅ (R
(2 ⋅ R
5 ⋅ R
5 ⋅ R
TC
TC
TH
) - (7 ⋅ R
TH
- R
OVP
⋅ R
⋅ R
AAT3697
TC
TH
. The AAT3697
)
TC
OVP
TH
)
).
If an
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