AAT3682ISN-4.2-T1(2005) データシートの表示（PDF） - Advanced Analogic Technologies

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AAT3682ISN-4.2-T1
(Rev.:2005)

Lithium-Ion/Polymer Linear 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.

AAT3682 features charge status output. Connecting

a LED to the STAT pin will display all the three con-

ditions 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 sum-

marizes the conditions.

3682.2005.02.1.1

Charge Status

No battery connected

Battery condition

cc

cv

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

cc

cv

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 MOS-

FET. If a reverse-blocking diode is added to the sys-

tem, 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.

15

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