AAT3682 查看數據表（PDF） - Advanced Analogic Technologies

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AAT3682

Lithium-Ion/Polymer Battery Charger

Advanced Analogic Technologies 

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

PMAX = (VIN(MAX) - VSENSE - VSCHOTTKY - VBAT(MIN)) ⋅ ICHG(MAX)

= (5.5V - 0.1V - 0.2V - 3.04V) ⋅ 550mA

= 1.2W

This equation can be used to determine the maxi-

mum input voltage given the maximum junction and

ambient temperature and desired charge current.

VIN(MAX) =

TJ(MAX) - TAMB

θ ⋅ ICHG(MAX)

+ VBAT + VSCHOTTKY + VCS

=

120°C - 70°C

50°C/W ⋅ 500mA

+ 3.1V + 0.2V + 0.1V

= 5.3V

Operation Under No-Load

Under no-load conditions (i.e., when the AAT3682 is

powered with no battery connected between the

BAT pin and VSS), the output capacitor is charged

up very quickly by the trickle charge control circuit to

the BAT pin until the output reaches the recharge

threshold (VRCH). At this point, the AAT3682 will

drop into sleep mode. The output capacitor will dis-

charge slowly by the capacitor's own internal leak-

age until the voltage seen at the BAT pin drops

below the VRCH threshold. This 100mV cycle will

continue at approximately 3Hz with a 0.1µF capaci-

tor 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 established by the COUT value. For

desktop charger applications, where it might not be

desirable to have a "charger ready" blinking LED, a

large COUT capacitor in the 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

No Battery Connected

Battery Condition

Constant Current

Constant Voltage

Sleep/Charge Complete

LED Display

Blinking

100% LED Light

75% LED Light

25% LED Light

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 con-

necting the T2X pin to VCC via 100kΩ resistor.

As the battery is transitioning from trickle charge to

constant 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

No Battery Connected

Battery Condition

Constant Current

Constant Voltage

Sleep/Charge Complete

LED Display

Blinking

On

On

On

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 bat-

tery 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.

3682.2006.12.1.3

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