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

Event Description

Charge Disabled or Low Supply

Charge Enabled Without Battery

Battery Charging

Charge Completed

Fault

STAT1

Off

Flash1

On

Off

On

Table 2: LED Display Status Conditions.

STAT2

Off

Flash1

Off

On

On

The LED anodes should be connected to VUSB.

The LEDs should be biased with as little current as

necessary to create reasonable illumination; there-

fore, a ballast resistor should be placed between

each of the LED cathodes and the STAT1/2 pins.

LED current consumption will add to the over-ther-

mal 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 indi-

vidual status LED.

The required ballast resistor value can be estimat-

ed using the following formulas:

Eq. 2: RB(STAT1/2) =

(VUSB - 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 sin-

gle strobe request protocol will invoke one of 14

possible return pulse counts in which the micro-

controller can look up based on the serial report

shown in Table 3.

The DATA pin function is active low and should nor-

mally be pulled high to VUSB. This data line may

also be pulled high to the same level as the high

state for the logic I/O port on the system microcon-

troller. In order for the DATA pin control circuit to

generate clean sharp edges for the data output and

to maintain the integrity of the data timing for the

system, the pull-up resistor on the data line should

be low enough in value so that the DATA signal

returns to the high state without delay. If the value

of the pull-up resistor used is too high, the strobe

pulse from the system microcontroller may exceed

the maximum pulse time and the DATA output con-

trol could issue false status reports. A 1.5kΩ resis-

tor is recommended when pulling the DATA pin

high to 5.0V at the VUSB input. If the data line is

pulled high to a voltage level less than 5.0V, the

pull-up resistor may be calculated based on a rec-

ommended minimum pull-up current of 3mA. Use

the following formula:

Eq. 3: RPULL-UP ≤

VPULL-UP

3mA

1. Flashing rate depends on output capacitance.

16

3685.2006.02.1.2

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