AAT3685IWP-4.2-1-T1 Ver la hoja de datos (PDF) - Analog Technology Inc

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AAT3685IWP-4.2-1-T1

Lithium-Ion/Polymer Battery Charger

Analog Technology Inc 

BatteryManagerTM

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 monitoring the voltage at the TS

pin. This system is intended for use negative temperature

coefficient (NTC) thermistors which are typically inte-

grated into the battery package. Most commonly used

NTC thermistors used in battery packs are approximately

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 within 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. Alternatively,

on the AAT3685-1, the TS pin may be left open.

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 indi-

cate 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 display definitions.

PRODUCT DATASHEET

AAT3685

Lithium-Ion/Polymer Battery Charger

Event Description

Charge Disabled or Low Supply

Charge Enabled Without Battery

Battery Charging

Charge Completed

Fault

STAT1

Off

Flash1

On

Off

On

STAT2

Off

Flash1

Off

On

On

Table 2: LED Display Status Conditions.

The LED anodes should be connected to VADP/USB. The

LEDs should be biased with as little current as necessary

to create reasonable illumination; therefore, a ballast

resistor should be placed between each of the LED cath-

odes and the STAT1/2 pins. LED current consumption

will add to the over-thermal power budget for the device

package, hence it is recommended to keep the LED drive

current to a minimum. 2mA should be sufficient to drive

most low-cost green, red, or multi-color LEDs. It is not

recommended to exceed 8mA for driving an individual

status LED.

The required ballast resistor value can be estimated

using the following formulas:

Eq. 2: RB(STAT1/2) =

(VAPD/USB - VF(LED))

ILED(STAT1/2)

Example:

RB(STAT1) =

(5.0V - 2.0V)

2mA

=

1.5kΩ

Note: Red LED forward voltage (VF) is typically 2.0V @

2mA.

Table 2 shows the four status LED display conditions.

Digital Charge Status Reporting

The AAT3685 has a comprehensive digital data reporting

system by use of the DATA pin feature. This function can

provide detailed information regarding the state of the

charging system. The DATA pin is a bi-directional port

which will read back a series of data pulses when the

system microcontroller asserts a request pulse. This

single strobe request protocol will invoke one of 14 pos-

sible return pulse counts in which the microcontroller can

look up based on the serial report shown in Table 3.

3685.2007.12.1.4

www.analogictech.com

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