AAT3603 datasheet(24/35 Pages) ANALOGICTECH

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AAT3603178

Total Power Solution for Portable Applications

PRODUCT DATASHEET

3603.2008.06.1.0

www .analogictech.com

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.

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 VBAT >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:

ICH = 800 ⋅ ⎛⎝

⎞

⎠

VISET

RISET

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

4.99

300

3.32

400

2.49

500

600

1.65

700

1.43

800

1.24

900

1.1

1000

Table 1: Constant Current Charge vs.

ISET Resistor Value.

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