PRODUCT DATASHEET
AAT2601178
Total Power Solution for Portable Applications
in the internal timing control circuit. The constant cur-
rent 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 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.
Power Saving Mode
After the charge cycle is complete, the battery charger
turns off the series pass device and automatically goes
into a power saving sleep mode. During this time, the
series pass device will block current in both directions to
prevent the battery from discharging through the battery
charger.
The battery charger will remain in sleep mode even if the
charger source is disconnected. It will come out of sleep
mode if either the battery terminal voltage drops below
the VRCH threshold, the charger EN pin is recycled, or the
charging source is reconnected. In all cases, the battery
charger will monitor all parameters and resume charging
in the most appropriate mode.
Programming Charge Current (ISET)
The default constant current mode charge level is user
programmed with a set resistor placed between the ISET
pin and ground. The accuracy of the constant charge cur-
rent, as well as the preconditioning trickle charge cur-
rent, is dominated by the tolerance of the set resistor. For
this reason, a 1% tolerance metal film resistor is recom-
mended for the set resistor function. The constant charge
current levels from 100mA to 1A may be set by selecting
the appropriate resistor value from Table 1 and Figure 5.
The ISET pin current to charging current ratio is 1 to 800.
It is regulated to 1.25V during constant current mode
unless changed using I2C commands. It can be used as a
charging current monitor, based on the equation:
Temperature Sense (TS)
The TS pin is available to monitor the battery tempera-
ture. Connect a 10k NTC resistor from the TS pin to
ground. The TS pin outputs a 75μA constant current into
the resistor and monitors the voltage to ensure that the
battery temperature does not fall outside the limits
depending on the temperature coefficient of the resistor
used. When the voltage goes above 2.39V or goes below
0.331V, the charging current will be suspended.
V
Charge Safety Timer (CT)
⎛
⎝
⎞
⎠
ISET
ICH = 800 ⋅
R
ISET
While monitoring the charge cycle, the AAT2601 utilizes
a charge safety timer to help identify damaged cells and
to ensure that the cell is charged safely. Operation is as
follows: upon initiating a charging cycle, the AAT2601
charges the cell at 12% of the programmed maximum
charge until VBAT >2.8V. If the cell voltage fails to reach
the preconditioning threshold of 2.8V (typ) before the
safety timer expires, the cell is assumed to be damaged
and the charge cycle terminates. If the cell voltage
exceeds 2.8V prior to the expiration of the timer, the
charge cycle proceeds into fast charge. There are three
timeout periods: 1 hour for Trickle Charge mode, 3 hours
for Constant Current mode, and 3 hours for Constant
Voltage mode.
During preconditioning charge, the ISET pin is regulated
to 12% of the fast charge current ISET voltage level
(Figure 5), but the equation stays the same. During con-
stant voltage charge mode, the ISET pin voltage will
slew down and be directly proportional to the battery
current at all times.
Constant Charging
Current ICH_CC (mA)
Set Resistor
Value (kΩ)
100
200
300
400
500
600
700
800
900
1000
10
4.99
3.32
2.49
2
1.65
1.43
1.24
1.1
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 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 unterminated, as this will cause errors
1
Table 1: Constant Current Charge vs.
ISET Resistor Value.
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2601.2008.01.1.0
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