AAT3685IWP-4.2-1-T1 データシートの表示（PDF） - Analog Technology Inc

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AAT3685IWP-4.2-1-T1

Lithium-Ion/Polymer Battery Charger

Analog Technology Inc 

BatteryManagerTM

Application Information

USB System Power Charging

The USB charge mode provides two programmable fast

charge levels up to 1A for each, SETH and SETL. The

SETH or SETL modes may be externally selected by the

select pin (PWRSEL). When the PWRSEL pin is con-

nected to a logic high level, the SETH level will be active.

Conversely, when PWRSEL is pulled to a logic low level

(ground), the SETL level will be used for fast charging.

These two charge levels may be user programmed to

any level between 50mA and 1A by selecting the appro-

priate resistor values for RSETH and RSETL. Refer to Table

1 for recommended RSETH and RSETL values for the desired

input constant current charge levels.

Charge Reduction

In many instances, product system designers do not

know the real properties of a potential port to be used

to supply power to the battery charger. Typical powered

USB ports commonly found on desktop and notebook

PCs should supply up to 500mA. In the event a port

being used to supply the charger is unable to provide the

programmed fast charge current, or if the system under

charge must also share supply current with other func-

tions, the AAT3685 will automatically reduce USB fast

charge current to maintain port integrity and protect the

host system.

The charge reduction system becomes active when the

voltage on the input falls below the charge reduction

threshold (VADP/USB_CHR), which is typically 4.5V. Regardless

of which charge function is selected (SETH or SETL), the

charge reduction system will reduce the fast charge cur-

rent level in a linear fashion until the voltage sensed on

the input recovers above the charge reduction threshold

voltage. The charge reduction threshold (VADP/USB_CHR)

may be externally set to a value lower than 4.5V by

placing a resistor divider network between VADP/USB and

ground with the center connected to the CHR pin. The

charge reduction feature may be disabled by connecting

a 10kΩ resistor from the CHR pin directly to the ADP/

USB input pin.

The following equation may be used to approximate a

USB charge reduction threshold below 4.5V:

Eq.

1:

V = ADP/USB_CHR

2.0V ÷

R12

R12 + R11

where R11/R12 << 1MΩ.

PRODUCT DATASHEET

AAT3685

Lithium-Ion/Polymer Battery Charger

ICC

50

75

100

200

300

400

500

600

700

800

900

1000

SETH

RSET (kΩ)

86.6

57.6

42.2

21.0

13.7

10.2

8.06

6.65

5.62

4.87

4.32

3.83

SETL

RSET (kΩ)

86.6

57.6

42.2

20.5

13.7

10.2

8.06

6.65

5.62

4.87

4.32

3.83

Table 1: Recommended RSET Values.

VADP/USB

ADP/USB

R11

CHR

R12

1.025M

VCHR = 2.0V

825k

Figure 2: Internal Equivalent Circuit

for the CHR Pin.

Input Charge Inhibit and Resume

The AAT3685 UVLO and power on reset feature will func-

tion when the input pin voltage level drops below the

UVLO threshold. At this point, the charger will suspend

charging and shut down. When power is re-applied to the

ADP/USB pin or the UVLO condition recovers, the system

charge control will assess the state of charge on the bat-

tery cell and will automatically resume charging in the

appropriate mode for the condition of the battery.

Single Path Charging from

a Line Adapter or USB Source

Most USB charging applications limit charging current to

500mA due to the limitations of a USB port as a power

source. The AAT3685 is capable of, and may be pro-

grammed for, constant current charge levels up to 1A.

Thus, charging operation is not just restricted to use

with USB port supplies. Any power source may be used

3685.2007.12.1.4

www.analogictech.com

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