AAT3685(2006) 查看數據表（PDF） - Analog Technology Inc

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AAT3685
(Rev.:2006)

Lithium-Ion/Polymer Battery Charger

Analog Technology Inc 

AAT3685

Lithium-Ion/Polymer Battery Charger

10000

1000

SETL

100

SETH

10

1

10

100

RSET (kΩ)

1000

Figure 3: IFASTCHARGE vs. RSET.

Protection Circuitry

Over-Voltage Protection

An over-voltage event is defined as a condition

where the voltage on the BAT pin exceeds the

maximum battery charge voltage and is set by the

over-voltage protection threshold (VOVP). If an

over-voltage condition occurs, the AAT3685 charge

control will shut down the device until voltage on

the BAT pin drops below the over-voltage protec-

tion threshold (VOVP). The AAT3685 will resume

normal charging operation after the over-voltage

condition is removed. During an over-voltage

event, the STAT LEDs will report a system fault; the

actual fault condition may also be read via the

DATA pin signal.

Over-Temperature Shutdown

The AAT3685 has a thermal protection control cir-

cuit which will shut down charging functions should

the internal die temperature exceed the preset

thermal limit threshold.

Battery Temperature Fault Monitoring

In the event of a battery over-temperature condi-

tion, the charge control will turn off the internal pass

device and report a battery temperature fault on the

DATA pin function. The STAT LEDs will also dis-

play a system fault. After the system recovers

from a temperature fault, the device will resume

charging operation.

The AAT3685 checks battery temperature before

starting the charge cycle, as well as during all

stages of charging. This is accomplished by moni-

toring the voltage at the TS pin. This system is

intended for use negative temperature coefficient

(NTC) thermistors which are typically integrated into

the battery package. Most commonly used NTC

thermistors used in battery packs are approximate-

ly 10kΩ at room temperature (25°C). The TS pin

has been specifically designed to source 80µA of

current to the thermistor. The voltage on the TS pin

that results from the resistive load should stay with-

in a window from 335mV to 2.32V. If the battery

becomes too hot during charging due to an internal

fault, the thermistor will heat up and reduce in value,

thus pulling the TS pin voltage lower than the TS1

threshold, and the AAT3685 will halt charging and

signal the fault condition. If the use of the TS pin

function is not required by the system, it should be

terminated to ground using a 10kΩ resistor.

Battery Charge Status Indication

The AAT3685 indicates the status of the battery

under charge with two different systems. First, the

device has two status LED driver outputs. These

two LEDs can indicate simple functions such as no

battery charge activity, battery charging, charge

complete, and charge fault. The AAT3685 also

provides a bi-directional data reporting function so

that a system microcontroller may interrogate the

DATA pin and read any one of 14 system states.

Status Indicator Display

Simple system charging status may be displayed

using one or two LEDs in conjunction with the

STAT1 and STAT2 pins on the AAT3685. These

two pins are simple switches to connect the display

LED cathodes to ground. It is not necessary to use

both display LEDs if a user simply wants to have a

single lamp to show "charging" or "not charging."

This can be accomplished by just using the STAT1

pin and a single LED. Using two LEDs and both

STAT pins simply gives the user more information

for charging states. Refer to Table 2 for LED dis-

play definitions.

3685.2006.02.1.2

15

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