AAT3682

DATA SHEET

Li-Ion/Polymer Linear Battery Charger

13

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

201884B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012

1

2

J1

1

2

3

J2

1K

R4

0.2Ω

R2

1K

R3

2.2K

R1

100K

R6

100K

R5

D2

22μF

C1

10μF

C2

Green LED

GND

D1

47nF

C3

TS

1

N/C

2

N/C

3

STAT

4

AAT3682

U1

100K

R7

2

1

3

SW-T2X

S1

1000pF

C4

4.7μF

C5

Remove capacitor for

progressive dimming

Figure 5: Evaluation Board Schematic.

Applications Information

Choosing a Sense Resistor

The charging rate recommended by lithium-ion/polymer

cell vendors is normally 1C, with a 2C absolute maximum

rating. Charging at the highest recommended rate offers

the advantage of shortened charging time without

decreasing the battery’s lifespan. This means that the

suggested fast charge rate for a 500mAH battery pack is

500mA. Refer to the Safe Operating Area curves in the

Typical Characteristics section of this datasheet to deter-

mine the maximum allowable charge current for a given

the charge current according to the following equation:

V

R

I

CHARGE

rent during fast charge, a 200m value resistor should

be selected. Calculate the worst case power dissipated in

the sense resistor according to the following equation:

V

CS

2

0.1V

2

P =

=

= 50mW

R

SENSE

0.2

Ω

A 500mW LRC type sense resistor from IRC is adequate

for this purpose. Higher value sense resistors can be

used, decreasing the power dissipated in the sense resis-

tor and pass transistor. The drawback of higher value

sense resistors is that the charge cycle time is increased,

so tradeoffs should be considered when optimizing the

design.

Thermistor

The AAT3682 checks battery temperature before starting

the charge cycle, as well as during all stages of charging.

This is accomplished by monitoring the voltage at the TS

pin. Either a negative temperature coefficient thermistor

(NTC) or positive-temperature coefficient thermistor

(PTC) can be used because the AAT3682 checks to see