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AAT3681A

500mA USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger

Analog Technology Inc 

AAT3681A

500mA USB Port or AC Adapter

Lithium-Ion/Polymer Battery Charger

Application Information

Adapter or USB Power Input

Constant current charge levels up to 500mA may

be programmed by the user when powered from a

sufficient input power source. The AAT3681A will

operate from the adapter input over a 4.0V to 7.5V

range. The constant current fast charge current for

the adapter input is set by the RSET resistor con-

nected between ISET and ground. Refer to Table 1

for recommended RSET values for a desired con-

stant current charge level.

Adapter Input Charge Inhibit and Resume

The AAT3681A has a UVLO and power on reset

feature so that if the input supply to the ADP pin

drops below the UVLO threshold, the charger will

suspend charging and shut down. When power is

re-applied to the ADP pin or the UVLO condition

recovers, the system charge control will assess the

state of charge on the battery cell and will auto-

matically resume charging in the appropriate mode

for the condition of the battery.

Enable / Disable

The AAT3681A provides an enable function to con-

trol the charger IC on and off. The EN pin functions

as follows on the various AAT3681A options:

AAT3681A and AAT3681A-1: The enable (EN) pin

is internally pulled down. When pulled to a logic

high level, the AAT3681A is enabled. When left

open or pulled to a logic low level, the AAT3681A

will be shut down and forced into the sleep state.

AAT3681A-2: The enable (EN) pin is internally

pulled down. When left open or pulled to a logic low

level, the AAT3681A-2 is enabled. When pulled to

a logic high level, the AAT3681A-2 will be shut

down and forced into the sleep state.

AAT3681A-3: The enable (EN) pin is not internally

pulled down. When pulled to a logic low level, the

AAT3681A-3 is enabled. When pulled to a logic

high level, the AAT3681A-3 will be shut down and

forced into the sleep state.

Charging will be halted regardless of the battery

voltage or charging state. When the device is re-

enabled, the charge control circuit will automati-

cally reset and resume charging functions with the

appropriate charging mode based on the battery

3681A.2007.10.1.2

charge state and measured cell voltage on the

BAT pin.

Programming Charge Current

The fast charge constant current charge level is

user programmed with a set resistor placed

between the ISET pin and ground. The accuracy of

the fast charge, as well as the preconditioning trick-

le charge current, is dominated by the tolerance of

the set resistor used. For this reason, a 1% toler-

ance metal film resistor is recommended for the set

resistor function. Fast charge constant current lev-

els from 15mA to 500mA may be set by selecting

the appropriate resistor value from Table 1.

Nominal

ICHARGE (mA)

500

450

400

350

300

250

200

150

100

50

40

30

20

15

Set Resistor

Value (kΩ)

3.24

3.57

4.12

4.64

5.36

6.49

8.06

10.7

16.2

31.6

38.3

53.6

78.7

105

Table 1: RSET Values.

1000

100

10

1

1

10

100

1000

RSET (kΩ)

Figure 2: Constant Charging Current

vs. Set Resistor Values.

11

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