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AAT3689

0.5A/1.0A USB Port/Adapter Lithium-Ion/Polymer Battery Charger

Advanced Analogic Technologies 

AAT3689

0.5A/1.0A USB Port/Adapter

Lithium-Ion/Polymer Battery Charger

The AAT3689 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 to use negative temperature coefficient

(NTC) thermistors, which are typically integrated

into the battery package. Most commonly used

NTC thermistors used in battery packs are approx-

imately 10kΩ at room temperature (25°C).

The TS pin has been specifically designed to

source 80μA of current to the thermistor. The volt-

age on the TS pin that results from the resistive

load should stay within a window from 330mV to

2.30V. If the battery becomes too hot during charg-

ing due to an internal fault, the thermistor will heat

up and reduce in value, thus pulling the TS pin volt-

age lower than the TS1 threshold and the AAT3689

will 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 AAT3689 has two status LED driver outputs.

These two LEDs can indicate simple functions

such as no battery charge activity, battery charg-

ing, charge complete, and charge fault.

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 AAT3689. These two

pins are simple switches to connect the LED cath-

odes to ground. It is not necessary to use both dis-

play LEDs if a user simply wants to have a single

lamp to show "charging" or "not charging." This can

be accomplished by using the STAT1 pin and a sin-

gle LED. Using two LEDs and both STAT pins sim-

ply gives the user more information to the charging

states. Refer to Table 3 for LED display definitions.

The LED anodes should be connected to either

VUSB or VADP, depending upon the system design

requirements. The LEDs should be biased with as

little current as necessary to create reasonable illu-

mination; therefore, a ballast resistor should be

placed between the LED cathodes and the

STAT1/2 pins. LED current consumption will add to

the overall thermal power budget for the device

package, so it is wise to keep the LED drive current

to a minimum. 2mA should be sufficient to drive

most low-cost green or red LEDs. It is not recom-

mended to exceed 8mA for driving an individual

status LED. The required ballast resistor value can

be estimated using the following formulas:

For connection to the adapter supply:

R = VI - V B(STAT1/2)

ADP

F(LED)

LED(STAT1/2)

Example:

RB(STAT1) =

5.5V - 2.0V

2mA

= 1.75kΩ

Note: Red LED forward voltage (VF) is typically

2.0V @ 2mA.

For connection to the USB supply:

R = VI - V B(STAT1/2)

USB

F(LED)

LED(STAT1/2)

Example:

RB(STAT2) =

5.0V - 3.2V

2mA

= 900Ω

Note: Green LED forward voltage (VF) is typically

3.2V @ 2mA.

The status LED display conditions are described in

Table 3.

3689.2006.11.1.0

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