AAT3682ISN-4.2-T1 - AnalogicTech

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 1

BatteryManager™

General Description

The AAT3682 is a lithium-ion/polymer linear battery

charger. It is designed for compact portable appli-

cations with a single cell battery. The AAT3682 pre-

cisely regulates battery charge voltage and charge

current, and offers an integrated pass device, mini-

mizing the number of external components required.

The AAT3682 charges the battery in three different

phases: preconditioning, constant current, and con-

stant voltage. In preconditioning mode, the charge

current has two different levels and is controlled by

one external pin. Battery charge temperature and

charge state are carefully monitored for fault condi-

tions. A battery charge stable monitor output pin is

provided to indicate the battery charge status

through a display LED or interface to a system con-

troller. The AAT3682 has the sleep mode option for

when the input supply is removed. In this mode, it

draws only 2.0µA of typical current.

The AAT3682 is available in a 16-pin QFN44 and is

specified over the -20°C to +70°C temperature

range.

Features

•V

IN Range: 4.7V to 6.0V

• Low Quiescent Current, Typically 0.5mA

• 1% Accurate Preset Voltage

• Up to 1A of Charging Current

• Integrated Pass Device

• Battery Temperature Monitoring

• Fast Trickle Charge Option

• Deep Discharge Cell Conditioning

• LED Charge Status Output or System

Microcontroller Serial Interface

• Power-On Reset

• Lower Power Sleep Mode

• Status Outputs for LED or System Interface

Indicates Charge and Fault Conditions

• Temperature Range: -20°C to +70°C

• 16-Pin QFN44 Package

Applications

• Cellular Telephones

• Digital Still Cameras

• Hand-Held PCs

• MP3 Players

• Personal Data Assistants (PDAs)

Typical Application

Gate

DRV

CSI

VCC

VSS

BAT

T2X

BSENSE

STAT

RSENSE

CIN = 10µF

COUT= 1µF

LED 1

R2= 1K

BATT+

BATT-

RT1

RT2

TEMP

dapter

Pin Description

Pin Configuration

QFN44-16

(Top View)

N/C

STAT

VSS

T2X

N/C

BAT

VSS

GATE

N/C

AAT3682

CSI

BSENSE

VCC

Pin # Symbol Function

1 TS Battery temperature sense input.

2, 3, 8, 12 N/C Not connected.

4 STAT Battery charger status output. Connect an LED in series with 2.2kΩfrom STAT to VIN

for a visual monitor battery charge state or connect to a microcontroller to monitor bat-

tery status. A 100kΩresistor should be placed between STAT and VIN for this function.

5 VSS Common ground connection.

6 DRV Battery charge control output.

7 T2X Battery trickle charge control input. Connect this pin to VSS to double the battery trickle

charge current. Leave this pin floating for normal trickle current (10% of full charge cur-

rent). To enter microcontroller fast-read status, pull this pin high during power up.

9 BAT Battery charge control output. Current regulated output to charge the battery. For best

operation, a 0.1µF ceramic capacitor should be placed between BAT and GND.

10 VSS Common ground connection.

11 Gate Input voltage for biasing the pass device.

13 VP Battery charge power input.

14 CSI Current sense input.

15 BSENSE Battery voltage sense input.

16 VCC AAT3682 bias input power.

EP Exposed paddle (bottom); connect to GND directly beneath the package.

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

23682.2005.02.1.1

Absolute Maximum Ratings1

Thermal Information

Symbol Description Value Units

θJA Maximum Thermal Resistance2, 3 50 °C/W

PDPower Dissipation (TA= 25°C) 2.0 W

Symbol Description Value Units

VIN VIN Relative to GND -0.3 to 6.0 V

VCSI CSI to GND -0.3 to VCC+0.3 V

VT2X T2X to GND -0.3 to 5.5 V

Bias, VBAT BAT to GND -0.3 to VCC+0.3 V

TJOperating Junction Temperature Range -40 to 85 °C

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 3

1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions

other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.

2. Mounted on an FR4 board.

3. Derate 20mW/°C above 25°C.

Electrical Characteristics1

VIN = 5.0V, TA= -20 to +70°C, unless otherwise noted. Typical values are at TA= 25°C.

Symbol Description Conditions Min Typ Max Units

VIN Operation Input Voltage 4.7 6.0 V

ICC Operating Current VIN = 5.5V, VCH = 4.2 0.5 3.0 mA

ISLEEP Sleep Mode Current VIN = 3.5V, VCH = 4.2 3.0 6.0 µA

ISTAT(HI) STAT High Level Output Leakage Current VIN = 5.5V -1.0 +1.0 µA

VSTAT(LOW) STAT Low Level Sink Current VIN = 5.5V, ISINK = 5mA 0.3 0.6 V

VCH Output Charge Voltage Regulation VBAT = 4.2V TA= 25°C 4.175 4.20 4.225 V

See Note 1 4.158 4.20 4.242

VCS Charge Current Regulation VIN = 5.5V, VCH = 4.2 90 100 110 mV

ICH Charge Current2VIN = 5.5V 1.0 A

VMIN Preconditioning Voltage Threshold VCH = 4.2V 3.04 3.1 3.16 V

VTRICKLE Trickle Charge Current Regulation T2X Floating; VCH = 4.2V 10 mV

T2X Trickle Charge Current Gain T2X = VSS 1.8

VTS1 Low Temperature Threshold 29.1 30 30.9 %VCC

VTS2 High Temperature Threshold 58.2 60 61.8 %VCC

VTERM Charge Termination Threshold Voltage 4 12 24 mV

VRCH Battery Recharge Voltage Threshold VCH = 4.2V 4.018 4.1 4.182 V

VUVLO Under-Voltage Lockout VIN Rising, TA= 25°C 3.5 4.0 4.5 V

VOVP Over-Voltage Protection Threshold 4.4 V

VOCP Over-Current Protection Threshold 200 %VCS

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

43682.2005.02.1.1

1. The AAT3682 output charge voltage is specified over 0°C to 55°C ambient temperature range; operation over -20°C to 70°C is guar-

anteed by design.

2. 1A of charging current is only for dynamic applications and not DC. In addition, the ambient temperature must be at or below 50°C.

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 5

Typical Characteristics

Trickle Charge Current vs. Temperature

(RSENSE = 0.15Ω)

Temperature (°C)

Trickle Charge Current

(mA)

130

135

140

145

150

155

160

165

170

-50 -25 0 25 50 75 100

Trickle Charge Threshold Voltage

vs.Temperature

(RSENSE = 0.15Ω)

Temperature (°C)

Trickle Charge Threshold Voltage

(V)

2.8

2.9

3.0

3.1

3.2

3.3

3.4

-50 -25 0 25 50 75 100

Regulated Output Voltage vs. Temperature

(RSENSE = 0.15Ω)

Temperature (°C)

Regulated Output Voltage (V)

4.100

4.125

4.150

4.175

4.200

4.225

4.250

-50 -25 0 25 50 75 100

Regulated Output Voltage vs. Input Voltage

(RSENSE = 0.15Ω)

Input Voltage

(V)

Regulated Output Voltage

(V)

4.00

4.10

4.20

4.30

4.40

4.0 4.5 5.0 5.5 6.0 6.5

Regulated Output Voltage vs. Charge Current

(RSENSE = 0.15Ω)

Charging Current (mA)

Regulated Output Voltage (V)

4.15

4.17

4.19

4.21

4.23

4.25

0 100 200 300 400 500 600 700

Battery Recharge Threshold Voltage

vs.Temperature

(RSENSE = 0.15Ω

)

Temperature (°C)

Battery Recharge

Threshold Voltage (V)

3.80

3.85

3.90

3.95

4.00

4.05

4.10

4.15

4.20

-50 -25 0 25 50 75 100

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

63682.2005.02.1.1

Typical Characteristics

Trickle Charge Current vs. Input Voltage

(RSENSE = 0.15Ω; 1.8X Mode)

Input Voltage (V)

Trickle Charge Current

(mA)

130

135

140

145

150

155

160

165

170

4.0 4.5 5.0 5.5 6.0

Charging Current vs. Battery Voltage

(RSENSE = 0.15Ω with External Schottky)

Battery Voltage (V)

Charging Current

(mA)

100

200

300

400

500

600

700

2.5 3.0 3.5 4.0 4.5 5.0

VIN = 4.5V VIN = 4.75V

VIN = 5.5V

Charging Current vs. Input Voltage

(RSENSE = 0.15Ω with External Schottky)

Input Voltage (V)

Charging Current

(mA)

100

200

300

400

500

600

700

4.0 4.5 5.0 5.5 6.0

VBAT = 4.1V

VBAT = 3.6V

Charging Current vs. Temperature

(RSENSE = 0.15Ω)

Temperature (°C)

Charging Current

(mA)

650

660

670

680

690

700

-50 -25 0 25 50 75 100

Typical Characteristics

Safe Operating Area

(TJ(MAX) = 150°C)

Charging Current (A)

Maximum Input Voltage (V)

5.0

5.2

5.4

5.6

5.8

6.0

6.2

0 0.2 0.4 0.6 0.8

TAMB = 85°C

TAMB = 70°C

TAMB = <50°C

Schottky VF = 0.2V

Safe Operating Area

(TJ(MAX) = 120°C)

Charging Current (A)

Maximum Input Voltage (V)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0.0 0.2 0.4 0.6 0.8

TAMB = 85°C

Schottky VF = 0.2V

TAMB = 70°C

TAMB = 50°CTAMB = 40°C

Charging Current vs. Battery Voltage

(RSENSE = 0.2Ω with External Schottky)

Battery Voltage (V)

Charging Current

(mA)

100

200

300

400

500

600

2.5 3.0 3.5 4.0 4.5 5.0

VIN = 4.5V

VIN = 4.75V

VIN = 5.5V

Trickle Charge Current vs. Input Voltage

(RSENSE = 0.2Ω; 1.8X Mode)

Input Voltage (V)

Trickle Charge Current

(mA)

100

102

104

4 4.5 5 5.5 6

Charging Current vs. Input Voltage

(RSENSE = 0.2Ω with External Schottky)

Input Voltage (V)

Charging Current

(mA)

100

200

300

400

500

600

4.0 4.5 5.0 5.5 6.0

VBAT = 4.0V

VBAT = 3.6V

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 7

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

83682.2005.02.1.1

Functional Block Diagram

MUX

T2X

LED Signal

Generator

Microcontroller

Status Generator

Microcontroller

Read Enable

Charge Status

Logic Control

Power-On

Reset

VSS

STAT

DRV

GATE

BAT

Under-Voltage

Lock Out

Over-Current /

Short-Circuit

Protection

2X Trickle

Charge

Control

Loop Select

MUX

Driver

VREF

Temperature

Sense

Comparator

Voltage

Comparator

Voltage Loop

Error Amp

Current Loop

Error Amp

VCC

BSENSE

T2X

CSI

Functional Description

The AAT3682 is a linear charger designed for single

cell lithium-ion/polymer batteries. It is a full-featured

battery management system IC with multiple levels

of power savings, system communication, and pro-

tection integrated inside. Refer to the block diagram

above and the flow chart and typical charge profile

graph (Figures 1 and 2) in this section.

Cell Preconditioning

Before the start of charging, the AAT3682 checks

several conditions in order to maintain a safe charg-

ing environment. The input supply must be above

the minimum operating voltage, or under-voltage

lockout threshold (VUVLO), for the charging

sequence to begin. Also, the cell temperature, as

reported by a thermistor connected to the TSpin,

must be within the proper window for safe charging.

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 9

Figure 1: AAT3682 Operational Flow Chart.

Figure 2: Typical Charge Profile.

Preconditioning

(Trickle Charge)

Phase Constant Current

Phase Constant Voltage

Phase

Output Charge

Voltage (VCH)

Preconditioning

Voltage Threshold

(VMIN)

Regulation

Current

(ICHARGE(REG))

Trickle Charge

and Termination

Threshold

UVLO

Temperature Test

TS > VTS1

TS < VTS2

Power On Reset

Preconditioning Test

Current Phase Test

VCH >VBAT

VMIN >VBAT

VTERM

RSENSE

<VRCH

Voltage

Phase Test

VCC> VUVLO Shut Down

Mode

Shut Down

Mode

Yes

Yes Low Current

Conditioning

Charge

Low Current

Conditioning

Charge

(Trickle Charge)

Temperature

Fault

Temperature

Fault No

Current

Charging

Mode

Current

Charging

Mode

Yes

Voltage

Charging

Mode

Voltage

Charging

Mode

< IBAT

Yes

Charge Complete

Latch Off

Charge Complete

Latch Off

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

10 3682.2005.02.1.1

When these conditions have been met and a bat-

tery is connected to the BAT pin, the AAT3682

checks the state of the battery. If the cell voltage is

below VMIN, the AAT3682 begins preconditioning

the cell. This is performed by charging the cell with

10% of the programmed constant-current amount.

For example, if the programmed charge current is

500mA, then the preconditioning mode (trickle

charge) current will be 50mA. Cell preconditioning

is a safety precaution for deeply discharged cells

and, furthermore, limits power dissipation in the

pass transistor when the voltage across the device

is largest. The AAT3682 features an optional T2X

mode, which allows faster trickle-charging at

approximately two times the default rate. This

mode is selected by connecting the T2X pin to VSS.

If an over-temperature fault is triggered, the fast

trickle-charge will be latched off, and the AAT3682

will continue at the default 10% charge current.

Constant Current Charging

The cell preconditioning continues until the voltage

on the BAT pin reaches VMIN. At this point, the

AAT3682 begins constant-current charging (fast

charging). Current level for this mode is pro-

grammed using a current sense resistor RSENSE

between the VCC and CSI pins. The CSI pin moni-

tors the voltage across RSENSE to provide feedback

for the current control loop. The AAT3682 remains

in constant current charge mode until the battery

reaches the voltage regulation point, VCH.

Constant Voltage Charging

When the battery voltage reaches VCH during con-

stant-current mode, the AAT3682 transitions to con-

stant-voltage mode. The regulation voltage is facto-

ry programmed to 4.2V. In constant-voltage opera-

tion, the AAT3682 monitors the cell voltage and ter-

minates the charging cycle when the voltage across

RSENSE decreases to approximately 10mV.

Charge Cycle Termination, Recharge

Sequence

After the charge cycle is complete, the AAT3682

shuts off the pass device and automatically enters

power-saving sleep mode. Either of two possible

conditions will bring the IC out of sleep mode: the

battery voltage at the BAT pin drops below VRCH

(recharge threshold voltage) or the AAT3682 is

reset by cycling the input supply through the

power-on sequence. Falling below VRCH signals the

IC that it is time to initiate a new charge cycle.

Sleep Mode

When the input supply is disconnected, the device

automatically enters power-saving sleep mode. Only

consuming an ultra-low 2µA current, the AAT3682

minimizes battery drain when it is not charging. This

feature is particularly useful in applications where

the input supply level may fall below the battery

charge or under-voltage lockout level. In such cases,

where the AAT3682 input voltage drops, the device

will enter the sleep mode and automatically resume

charging once the input supply has recovered from

its fault condition. This makes the AAT3682 well suit-

ed for USB battery charger applications.

Charge Inhibit

The AAT3682 charging cycle is fully automatic;

however, it is possible to stop the device from

charging even when all conditions are met for prop-

er charging. Switching the TSpin to either VIN or

GND will force the AAT3682 to turn off the pass

device and wait for a voltage between the low and

high temperature voltage thresholds.

Resuming Charge and the VRCH

Threshold

The AAT3682 will automatically resume charging

under most conditions when a battery charge cycle

is interrupted. Events such as an input supply

interruption or under voltage, removal and replace-

ment of the battery under charge, or charging a

partially drained battery are all possible. The

AAT3682 will monitor the battery voltage and auto-

matically resume charging in the appropriate mode

based upon the measured battery cell voltage.

This feature is useful for systems with an unstable

input supply, which could be the case when power-

ing a charger from a USB bus supply. It is also

beneficial for charging or "topping off" partially dis-

charged batteries. The only restriction on resum-

ing charge of a battery is that the battery cell volt-

age must be below the battery recharge voltage

threshold (VRCH) specification. There is VRCH

threshold hysteresis built into the charge control

system. This is done to prevent the charger from

erroneously turning on and off once a battery

charge cycle is complete.

For example, the AAT3682 has a typical VRCH

threshold of 4.1V. A battery under charge is above

4.1V, but is still in the constant voltage mode

because it has not yet reached 4.2V to complete

the charge cycle. If the battery is removed and

then placed back on the charger, the charge cycle

will not resume until the battery voltage drops

below the VRCH threshold. In another case, a bat-

tery under charge is in the constant current mode

and the cell voltage is 3.7V when the input supply

is inadvertently removed and then restored. The

battery is below the VRCH threshold and the charge

cycle will immediately resume where it left off.

LED Display Charge Status Output

The AAT3682 provides a battery charge status out-

put via the STAT pin. STAT is an open-drain serial

data output cap able of displaying five distinct status

functions with one LED connected between the

STAT pin and VP. There are four periods which

determine a status word. Under default conditions,

each output period is one second long; thus one

status word will take four seconds to display

through an LED. The five modes include:

1. Sleep/Charge Complete: The IC goes into

Sleep mode when no battery is present -OR-

when the charge cycle is complete.

2. Fault: When an Over-Current (OC) condition

is detected by the current sense and control

circuit -OR- when an Over-Voltage (OV) con-

dition is detected at the BAT pin -OR- when a

battery Over-Temperature fault is detected

on the TEMP pin.

3. Battery Conditioning: When the charge sys-

tem is in the 1X or 2X trickle charge mode.

4. Constant Current (CC) Mode: When the sys-

tem is in the constant current charge mode.

5. Constant Voltage (CV) Mode: When the sys-

tem is in the constant voltage charge mode.

An additional feature of the LED status display is for

a Battery Not Detected state. When the AAT3682

senses there is no battery connected to the BAT

pin, the STAT output will turn the LED on and off at

a rate dependent on the size of the output capacitor

being used. The LED cycles on for two periods then

remains off for two periods. See Figure 3 below.

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 11

Figure 3: LED Display Output.

Sleep / Charge Complete

Temp., OC, OV Fault

Battery Conditioning

Constant Current Mode

Constant Voltage Mode

off / off / off / off

on / on / off / off

on / on / on / on

on / off / off / off

on / on / on / off

Charge Status Output Status LED Display

on/off

OFF

on/off on/off on/off

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

12 3682.2005.02.1.1

High-Speed Data Reporting

An optional system microcontroller interface can be

enabled by pulling the T2X pin up to 4.5V to 5.5V

during power-up sequence. The T2X pin should be

pulled high with the use of a 100kΩresistor. If the

input supply to VIN will not exceed 5.5V, then the

T2X pin may be tied directly to VIN through a

100KΩresistor. Since this is a TTL level circuit, it

may not be pulled higher than 5.5V without risk of

damage to the device.

When the high-speed data report feature is

enabled, the STAT output periods are sped up to

40µs, making the total st atus word 160µs in length.

See Figure 4 below.

An additional feature is the Output Status for the

Battery Not Detected state. When the AAT3682

senses there is no battery connected to the BAT

pin, the STAT pin cycles for two periods, then

remains off for two periods. When in High-Speed

Data Reporting, the AAT3682 will only trickle

charge at the 2X trickle charge level. This is

because the T2X pin is pulled high to enable the

high-speed data reporting. A status display LED

may not be connected to the STAT pin when the

high-speed data reporting is being utilized. If both

display modes are required, the display LED must

be switched out of the circuit before the T2X pin is

pulled high. Failing to do so could cause problems

with the high-speed switching control circuits inter-

nal to the AAT3682.

Charge Complete LED Status Mode

A simplified LED status can be obtained by config-

uring the AAT3682 for high-speed data recording

mode (T2X tied to VCC) and installing a 0.047µF

capacitor from the STAT pin to the VSS pin (see

Figure 5). In this configuration, the LED will be illu-

minated for all modes except the Sleep/Charge

Complete mode. In addition, the T2X input must be

tied to VCC through a 100kΩresistor. In this mode,

the trickle charge current will be 1.8X the normal

trickle charge level. To reset the trickle charge cur-

rent to the 1X level, the TSinput must be temporar-

ily toggled low. Removing C3 forces the LED status

to gradually dim out as the battery becomes fully

charged (see Figure 5).

Figure 4: Microcontroller Interface Logic Output.

Sleep / Charge Complete

Temp., OC, OV Fault

Battery Conditioning

Constant Current Mode

Constant Voltage Mode

HI / HI / HI / HI

LO / LO / HI / HI

LO / LO / LO / LO

LO / HI / HI / HI

LO / LO / LO / HI

Charge Status Output Status STAT Level

Protection Circuitry

The AAT3682 is a highly integrated battery manage-

ment system IC including several protection fea-

tures. In addition to battery temperature monitoring,

the IC constantly monitors for over-current and over-

voltage conditions; if an over-current situation

occurs, the AAT3682 latches off the pass device to

prevent damage to the battery or the system, and

enters shutdown mode until the over-current event is

terminated. An over-volt age condition is defined as a

condition where the voltage on the BAT pin exceeds

the maximum battery charge voltage. If an over-volt-

age condition occurs, the IC turns off the pass

device until voltage on the BAT pin drops below the

maximum battery charge constant volt age threshold.

The AAT3682 will resume normal operation after the

over-current or over-voltage condition is removed.

During an over-current or over-voltage event, the

STAT will report a FAULT signal. In the event of a

battery over-temperature condition, the IC will turn

off the p ass device and report a FAULT signal on the

STAT pin. After the system recovers from a temper-

ature fault, the IC will resume operation in the 1X

trickle charge mode to prevent damage to the sys-

tem in the event a defective battery is placed under

charge. Once the battery voltage rises above the

trickle charge to constant current charge threshold,

the IC will resume the constant current mode.

Applications Information

Choosing a Sense Resistor

The charging rate recommended by Lithium-Ion

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

maximum rating. Charging at the highest recom-

mended rate offers the advantage of shortened

charging time without decreasing the battery's lifes-

pan. 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 input voltage. The current sense resistor,

RSENSE, programs the charge current according to

the following equation:

Where ICHARGE is the desired typical charge current

during constant-current charge mode. VCC - VCSI is

the voltage across RSENSE, shown in the Electrical

Characteristic table as VCS. To program a nominal

500mA charge current during fast-charge, a

200mΩvalue resistor should be selected.

- V

CSI

SENSE

CHARGE

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 13

Figure 5: Evaluation Board Schematic.

0.2Ω

2.2K

100K

22µF

10µF

Green LED

GND

47nF

1N/C

2N/C

3STAT

VSS 5

DRV 6

T2X 7

N/C 8

BAT 9

VSS 10

Gate 11

N/C 12

13 CSI

14 BSENSE

15 VCC

AAT3682

100K

SW-T2X

1000pF

4.7

µF

Remove capacitor for

progressive dimming

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

14 3682.2005.02.1.1

Calculate the worst case power dissipated in the

sense resistor according to the following equation:

A 500mW LRC type sense resistor from IRC is

adequate for this purpose. Higher value sense

resistors can be used, decreasing the power dissi-

pated in the sense resistor 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 st ages

of charging. This is accomplished by monitoring the

voltage at the TSpin. Either a negative temperature

coefficient thermistor (NTC) or positive-temperature

coefficient thermistor (PTC) can be used because

the AAT3682 checks to see that the voltage at TSis

within a voltage window bounded by VTS1 and VTS2.

Please see the following equations for specifying

resistors:

RT1 and RT2 for use with NTC Thermistor

RT1 and RT2 for use with PTC Thermistor

Where RTC is the thermistor's cold temperature

resistance and RTH is the thermistor's hot tempera-

ture resistance. See thermistor specifications for

additional information. To ensure there is no

dependence on the input supply changes, connect

divider between VCC and VSS. Disabling the tem-

perature-monitoring function is achieved by apply-

ing a voltage between VTS1 and VTS2 on the TSpin.

Capacitor Selection

Input Capacitor

In general, it is good design practice to place a

decoupling capacitor between the VCC and VSS

pins. An input capacitor in the range of 1µF to 10µF

is recommended. If the source supply is unregu-

lated, it may be necessary to increase the capaci-

tance to keep the input voltage above the under-

voltage lockout threshold. If the AAT3682 is to be

used in a system with an external power supply

source, such as a typical AC-to-DC wall adaptor,

then a CIN capacitor in the range of 10µF should be

used. Alarger input capacitor in this application will

minimize switching or power bounce effects when

the power supply is "hot plugged" in.

Output Capacitor

The AAT3682 does not need an output capacitor for

stability of the device itself. However, a capacitor

connected between BAT and VSS will control the

output voltage when the AAT3682 is powered up

when no battery is connected. The AAT3682 can

become unstable if a high impedance load is placed

across the BAT pin to VSS. Such a case is possible

with aging Li-Ion battery cells. As cells age through

repeated charge and discharge cycles, the internal

impedance can rise over time. A10µF or larger out-

put capacitor will compensate for the adverse

effect s of a high impedance load and assure device

stability over all operating conditions.

Power Dissipation

The voltage drop across the VPand BAT pins mul-

tiplied times the charge current is used to deter-

mine the internal power dissipation. The maximum

power dissipation occurs when the input voltage is

at a maximum and the battery voltage is at the min-

imum preconditioning voltage threshold. This

power is then multiplied times the package theta to

determine the maximum junction temperature. The

worst case power junction temperature is calculat-

ed as follows.

RT1 =

5 • RTH • RTC

3 • (RTC - RTH)

RT2 =

5 • RTH • RTC

(2 • RTH) - (7 • RTC)

RT1 =

5 • RTH • RTC

3 • (RTC - RTH)

RT2 =

5 • RTH • RTC

(2 • RTC) - (7 • RTH)

0.1V

P = = = 50mW

SENSE 0.2Ω

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 15

This equation can be used to determine the maxi-

mum input voltage given the maximum junction and

ambient temperature and desired charge current.

Operation Under No-Load

Under no-load conditions (i.e., when the AAT3682 is

powered with no battery connected between the

BAT pin and VSS), the output capacitor is charged up

very quickly by the trickle charge control circuit to the

BAT pin until the output reaches the recharge

threshold (VRCH). At this point, the AAT3682 will

drop into sleep mode. The output capacitor will dis-

charge slowly by the capacitor's own internal leak-

age until the voltage seen at the BAT pin drops

below the VRCH threshold. This 100mV cycle will

continue at approximately 3Hz with a 0.1µF capaci-

tor connected. A larger capacitor value will produce

a slower voltage cycle. This operation mode can be

observed by viewing the STAT LED blinking on and

off at the rate established by the COUT value. For

desktop charger applications, where it might not be

desirable to have a "charger ready" blinking LED, a

large COUT capacitor in the range of 100µF or more

would prevent the operation of this mode.

AAT3682 features charge status output. Connecting

a LED to the STAT pin will display all the three con-

ditions of battery operation. Once the adapter is

connected to the battery charger, the LED will be

fully illuminated. As the battery charges, the LED

will gradually dim as it transitions to constant current

mode and to constant voltage mode. Table 1 sum-

marizes the conditions.

Table 1: Charging Status.

For applications where gradual dimming of the LED

is not desired, adding C3 (refer to Figure 5) between

the STAT pin and VSS will alter the charging status.

In addition, the AAT3682 must be configured to

operate in the high frequency STAT mode by con-

necting the T2X pin to VCC via 100KΩresistor.

As the battery is transitioning from trickle charge to

constant current charge and constant voltage, the

LED will remain illuminated. Once the battery is fully

charged, the LED will shut off indicating completion

of charge. Table 2 summarizes the conditions.

Table 2: Charging Status With C3 Connected.

Reverse Current Blocking Diode

A reverse-blocking diode is generally required for

the circuit shown in Figure 5.

The blocking diode gives the system protection from

a shorted input. If there is no other protection in the

system, a shorted input could discharge the battery

through the body diode of the internal pass MOS-

FET. If a reverse-blocking diode is added to the sys-

tem, a device should be chosen that can withstand

the maximum constant-current charge current at the

maximum system ambient temperature.

Additionally, the blocking diode will prevent the bat-

tery from being discharged to the UVLO level by

the AAT3682 in the event that power is removed

from the input to the AAT3682. For this reason, the

blocking diode must be placed in the location

shown in Figure 5.

Charge Status LED Display

No battery connected Blinking

Battery condition On

cc On

cv On

Sleep/charge complete Off

Charge Status LED Display

No battery connected blinking

Battery condition 100% LED light

cc 75% LED light

cv 25% LED light

Sleep/charge complete off

J(MAX)

- T

AMB

IN(MAX)

= + V

BAT

+ V

SCHOTTKY

+ V

= + 3.1V + 0.2V + 0.1V

= 5.3V

θ ⋅ I

CHG(MAX)

120°C - 70°C

50°C/W ⋅ 500mA

PMAX = (VIN(MAX) - VSENSE - VSCHOTTKY - VBAT(MIN)) ⋅ ICHG(MAX)

= (5.5V - 0.1V - 0.2V - 3.04V) ⋅ 550mA

= 1.2W

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

16 3682.2005.02.1.1

Diode Selection

Typically, a Schottky diode is used in reverse cur-

rent blocking applications with the AAT3682. Other

lower cost rectifier type diodes may also be used to

save cost if sufficient input power supply head

room is available.

The blocking diode selection should based on merits

of the device forward voltage (VF), current rating,

input supply level versus the maximum battery

charge voltage, and cost.

First, one must determine the appropriate minimum

diode forward voltage drop. Refer to the following

equation:

VIN(MIN) = VBAT(MAX) + VF(TRAN) + VF(DIODE)

Where:

VIN(MIN) = Minimum input supply level

VBAT(MAX) = Maximum battery charge voltage required

VF(TRAN) = Pass transistor forward voltage drop

VF(DIODE) = Blocking diode forward voltage

Based on the maximum constant current charge

level set for the system, the next step is to determine

the minimum current rating and power handling

capacity for the blocking diode. The constant current

charge level itself will dictate what the minimum cur-

rent rating must be for a given blocking diode. The

minimum power handling capacity must be calculat-

ed based on the constant current amplitude and the

diode forward voltage (VF):

Where:

PD(MIN) = Minimum power rating for a diode selection

VF= Diode forward voltage

ICC = Constant current charge level for the system

Schottky Diodes

Schottky diodes are selected for this application

because they have a low forward voltage drop, typi-

cally between 0.3V and 0.4V. A lower VFpermits a

lower voltage drop at the constant current charge

level set by the system; less power will be dissipated

in this element of the circuit. A Schottky diode allows

for lower power dissipation, smaller component

package sizes, and greater circuit layout densities.

Rectifier Diodes

Any general purpose rectifier diode can be used with

the AAT3682 application circuit in place of a higher

cost Schottky diode. The design trade-off is that a

rectifier diode has a high forward voltage drop. VF

for a typical silicon rectifier diode is in the range of

0.7V. A higher VFwill place an input supply voltage

requirement for the battery charger system. This will

also require a higher power rated diode since the

voltage drop at the constant current charge ampli-

tude will be greater. Refer to the previously stated

equations to calculate the minimum VIN and diode

PDfor a given application.

D(MIN)

= I

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

3682.2005.02.1.1 17

Figure 6: Evaluation Board Top Side Layout. Figure 7: Evaluation Board Bottom Side Layout.

Reference

Component

Designator Description Footprint Part Number Manufacturer

U1 Battery Charger AAT3682 QFN44-16 AAT3682-4.2 AnalogicTech

C1 Ceramic Capacitor 20µF-10V-X5R 1210 GRM32ER61A226KA65L muRata

C2 Ceramic Capacitor 10µF-10V-X5R 0805 GRM21BR61A106KE19L muRata

C3 Ceramic Capacitor 0.047µF-10V-X7R 0805 VJ0805Y473KXQA Vishay

R1 Resistor 2.2KΩ1/4W 0402 CRCW04022211F Vishay

R2 Current Sensing Resistor 0.2Ω1/4W 0805 RL1220S-R20-F SSM Susumu

R3 Resistor 1.0KΩ1% 1/4W 0402 CRCW04021003F Vishay

R4 Resistor 1.0KΩ1% 1/4W 0402 CRCW04021001F Vishay

R5 Resistor 100KΩ1% 1/4W 0402 CRCW04021003F Vishay

R6 Resistor 100KΩ1% 1/4W 0402 CRCW04021003F Vishay

R7 Resistor 100KΩ1% 1/4W 0402 CRCW04021003F Vishay

J1 4-Pin Socket Connector 4 Pin 277-1273-ND

J2 6-Pin Socket Connector 6 Pin 277-1274-ND

S1 Jumper Stand Switch 2 mm Jumper S2105-40-ND

D1 Green LED 1206 L62215CT-ND Chicago Miniature

D2 3.0A Schottky Diode SMA B340LADITR-ND Diodes Incorporated

Ordering Information

Package Information

All dimensions in millimeters.

4.000 ± 0.050

Pin 1 Dot By Marking

2.400 ± 0.050

0.600 ± 0.050

4.000 ± 0.050 2.280 REF

0.650 BSC

0.900 ± 0.050

Pin 1 Identification

R0.030Max

13 16

0.450 ± 0.050

0.0125 ± 0.0125

0.203 ± 0.025

0.330 ± 0.050

Top View Bottom View

Side View

Output Voltage Package Marking1Part Number (Tape and Reel)2

4.2V QFN44-16 MGXXY AAT3682ISN-4.2-T1

AAT3682

Lithium-Ion/Polymer Linear Battery Charger

18 3682.2005.02.1.1

Advanced Analogic Technologies, Inc.

830 E. Arques Avenue, Sunnyvale, CA 94085

Phone (408) 737-4600

Fax (408) 737-4611

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rights, or other intellectual property rights are implied.

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other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily

performed.

1. XYY = assembly and date code.

2. Sample stock is generally held on part numbers listed in BOLD.