AAT3603 Datasheet, PDF (24/35 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

PRODUCT DATASHEET
AAT3603178
Total Power Solution for Portable Applications
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 V_RCH 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.
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.
Charge Safety Timer (CT)
While monitoring the charge cycle, the AAT3603 utilizes a
charge safety timer to help identify damaged cells and to
ensure that the cell is charged safely. Operation is as fol-
lows: upon initiating a charging cycle, the AAT3603 charg-
es the cell at 12% of the programmed maximum charge
until V_BAT >2.8V. If the cell voltage fails to reach the pre-
conditioning 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 pro-
ceeds 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.
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
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.
Programming Charge Current (ISET)
At initial power-on, the charge current is always set to
100mA. The constant current mode charge level is user
programmed with the I²C interface and a set resistor
placed between the ISET pin and ground. The accuracy of
the constant charge current, as well as the precondition-
ing trickle charge current, is dominated by the tolerance
of the set resistor. For this reason, a 1% tolerance metal
film resistor is recommended for the set resistor function.
The programmable constant charge current levels from
100mA to 1A may be set by selecting the appropriate
resistor value from Table 1, Figure 5, and Table 3. 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:
I_CH
=
800
⋅
⎛
⎝
V_ISET⎞
R_ISET⎠
During preconditioning charge, the ISET pin is regulated
to 12% of the fast charge current I_SET 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 I_{CH_CC} (mA)
100
200
300
400
500
600
700
800
900
1000
Set Resistor
Value (kΩ)
10
4.99
3.32
2.49
2
1.65
1.43
1.24
1.1
1
Table 1: Constant Current Charge vs.
I_SET Resistor Value.
24
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