AAT3682

DATA SHEET

Li-Ion/Polymer Linear Battery Charger

15

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continue at approximately 3Hz with a 0.1μF capacitor

connected. A larger capacitor value will produce a slower

voltage cycle. This operation mode can be observed by

viewing the STAT LED blinking on and off at the rate

cations, where it might not be desirable to have a “char-

range of 100μF or more would prevent the operation of

this mode.

The AAT3682 features a charge status output. Connecting

a LED to the STAT pin will display all the three conditions

of battery operation. Once the adapter is connected to

the battery charger, the LED will be fully illuminated. As

the battery charges, the LED will gradually dim as it

transitions to constant current mode and to constant

voltage mode. Table 1 summarizes the conditions.

Charge Status

LED Display

No Battery Connected

Blinking

Battery Condition

100% LED Light

Constant Current

75% LED Light

Constant Voltage

25% LED Light

Sleep/Charge Complete

Off

Table 1: Charging Status.

For applications where gradual dimming of the LED is not

desired, adding C3 (refer to Figure 5) between the STAT

pin and VSS will alter the charging status. In addition,

the AAT3682 must be configured to operate in the high

frequency STAT mode by connecting the T2X pin to VCC

via 100k resistor.

As the battery is transitioning from trickle charge to con-

stant current charge and constant voltage, the LED will

remain illuminated. Once the battery is fully charged,

the LED will shut off, indicating completion of charge.

Table 2 summarizes the conditions.

Charge Status

LED Display

No Battery Connected

Blinking

Battery Condition

On

Constant Current

On

Constant Voltage

On

Sleep/Charge Complete

Off

Table 2: Charging Status With C3 Connected.

Reverse Current Blocking Diode

A reverse blocking diode is generally required for the

circuit shown in Figure 5. The blocking diode gives the

system protection from a shorted input. If there is no

other protection in the system, a shorted input could

discharge the battery through the body diode of the

internal pass MOSFET. If a reverse blocking diode is

added to the system, a device should be chosen that can

withstand the maximum constant current charge current

at the maximum system ambient temperature.

Additionally, the blocking diode will prevent the battery

from being discharged to the UVLO level by the AAT3682

in the event that power is removed from the input to the

AAT3682. For this reason, the blocking diode must be

placed in the location shown in Figure 5.

Diode Selection

Typically, a Schottky diode is used in reverse current

blocking applications with the AAT3682. Other lower cost

rectifier type diodes may also be used if sufficient input

power supply headroom is available.

The blocking diode selection should based on merits of

supply level versus the maximum battery charge volt-

age, and cost.

First, one must determine the appropriate minimum

diode forward voltage drop:

Where:

Based on the maximum constant current charge level set

for the system, the next step is to determine the mini-

mum current rating and power handling capacity for the

blocking diode. The constant current charge level itself

will dictate what the minimum current rating must be for

a given blocking diode. The minimum power handling

capacity must be calculated based on the constant cur-

V

F

P

I

CC

Where: