AAT3688 查看數據表（PDF） - Advanced Analog Technology, Inc.

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AAT3688

USB Port Lithium-Ion/Polymer Battery Charger

Advanced Analog Technology, Inc. 

AAT3688

USB Port Lithium-Ion/Polymer Battery Charger

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 AAT3688 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

16

3688.2006.10.1.5

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