General Description

The AAT3685 BatteryManagerTM is a member of

AnalogicTech's Total Power Management ICTM

(TPMICTM) product family. This device is a highly

integrated single cell lithium-ion/polymer battery

charger IC designed to operate with USB port or

line adapter inputs. It requires the minimum number

of external components.
The AAT3685 precisely regulates battery charge volt-

age and current for 4.2V lithium-ion/polymer battery

cells. Regardless of the type of input power source

(USB or adapter), the AAT3685 can be programmed

for two separate constant current charge levels up to

1A. An optional Charge Reduction Loop is built in to

allow users to charge the battery with available cur-

rent from the charge supply, while keeping the port

voltage regulated.
Battery temperature and charge state are fully

monitored for fault conditions. In the event of an

over-voltage or over-temperature failure, the

device will automatically shut down, thus protecting

the charging device, control system, and the bat-

tery under charge. Status monitor output pins are

provided to indicate the battery charge status by

directly driving two external LEDs. A serial interface

output is available to report any one of 14 various

status states to a microcontroller.
The AAT3685 is available in a Pb-free, thermally-

enhanced, space-saving 12-pin 3x3mm TDFN

package and is rated over the -40°C to +85°C tem-

perature range.

Features

Adapter or USB Charger

-- Programmable up to 1A Max

4.0V to 5.5V Input Voltage Range

High Level of Integration With Internal:

-- Charging Device

-- Reverse Blocking Diode

-- Current Sensing

Automatic Recharge Sequencing

Charge Reduction Loop

Battery Temperature Monitoring

Full Battery Charge Auto Turn-Off

Over-Voltage Protection

Emergency Thermal Protection

Power On Reset and Soft Start

Serial Interface Status Reporting

12-Pin 3x3mm TDFN Package

Applications

Cellular Telephones

Digital Still Cameras

Hand-Held PCs

MP3 Players

Personal Data Assistants (PDAs)

Other Lithium-Ion/Polymer Battery-Powered

Devices

AAT3685

Lithium-Ion/Polymer Battery Charger

Typical Application

AAT3685

C2
10

µF

BATT-

TEMP

Adapter or USB Input

Battery Pack

Serial Data

ADP/USB

PWRSEL

GND

BAT

BATT+

Input Hi/Lo Select

STAT1

SETH

SETL

CHR

STAT2

DATA

Enable

3685.2006.02.1.2

BatteryManager

Pin Descriptions

Pin Configuration

TDFN33-12

(Top View)

ADP/USB

BAT

GND

CHR

SETH
SETL
PWRSEL
STAT1
STAT2
DATA

Pin #

Name

Type

Function

ADP/USB

Line adapter or USB power supply input.

BAT

In/Out

Battery charging and sensing.

GND

Ground

Ground connection.

CHR

In/Out

Resistor divider to set USB voltage regulation for charge reduction mode.
Leave this pin open for default 4.5V USB regulation point. Tie to ADP/USB
pin to disable this function.

Enable pin. Logic high enables the IC.

In/Out

Connect to 10k NTC thermistor.

DATA

In/Out

Status report to microcontroller via serial interface, open-drain.

STAT2

Out

Battery charge status indicator pin to drive an LED: active low, open-drain.

STAT1

Out

Battery charge status indicator pin to drive an LED: active low, open-drain.

PWRSEL

When ADP/USB is present, use this pin to toggle between SETH and SETL
charging levels.

SETL

In/Out

Connect resistor here to set charge current for low-current port.

SETH

In/Out

Connect resistor here to set charge current for high-current port.

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

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Absolute Maximum Ratings

Thermal Information

Symbol

Description

Value

Units

Maximum Thermal Resistance (3x3mm TDFN)

°C/W

Maximum Power Dissipation

2.0

Symbol

Description

Value

Units

ADP/USB Input Voltage, <30ms, Duty Cycle <10%

-0.3 to 7.0

ADP/USB Input Voltage, Continuous

-0.3 to 6.0

BAT, PWRSEL, SETH, SETL, STAT1, STAT2, DATA, TS, CHR, EN

-0.3 to V

+ 0.3

Operating Junction Temperature Range

-40 to 150

°C

LEAD

Maximum Soldering Temperature (at leads)

300

°C

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

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

tions 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.

Electrical Characteristics

ADP

= 5V, T

= -25°C to +85°C, unless otherwise noted. Typical values are at T

= 25°C.

Symbol

Description

Conditions

Min

Typ

Max Units

Operation

ADP/USB Input Voltage Range

4.0

5.5

UVLO

Under-Voltage Lockout

Rising Edge

3.0

Under-Voltage Lockout Hysteresis

150

Operating Current

CC Charge Current = 500mA

0.75

1.5

SLEEP

Sleep Mode Current

BAT

= 4.25V

0.3

1.0

µA

Leakage

Reverse Leakage Current from

BAT

= 4V, ADP/USB Pin

1.0

µA

BAT Pin

Open

Voltage Regulation

BAT_EOC

End of Charge Voltage Accuracy

4.158

4.2

4.242

BAT

EOC Voltage Tolerance

0.5

MIN

Preconditioning Voltage Threshold

2.8

3.0

3.15

RCH

Battery Recharge Voltage Threshold

BAT_EOC

- 0.1

ADP/USB_CHR

Charge Reduction Regulation

No Connection on CHR Pin

4.3

4.5

4.64

CHR

CHR Pin Voltage Accuracy

1.9

2.0

2.1

Current Regulation

Charge Current

1000

Charge Current Regulation

Tolerance

SETH

SETH Pin Voltage

CC Mode

2.0

SETL

SETL Pin Voltage

CC Mode

2.0

IUH

Current Set Factor: I

CHARGE

SETH

2000

IUL

Current Set Factor: I

CHARGE

SETL

2000

Charging Devices

DS(ON)U

Charging MOSFET Transistor

= 5.5V

0.4

0.5

0.65

On Resistance

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

1. The AAT3685 output charge voltage is specified over the 0° to 70°C ambient temperature range; operation over the -25°C to +85°C

temperature range is guaranteed by design.

Electrical Characteristics

ADP

= 5V, T

= -25°C to +85°C, unless otherwise noted. Typical values are at T

= 25°C.

Symbol

Description

Conditions

Min Typ

Max Units

Logic Control / Protection

PWRSEL(H)

Input High Threshold

1.6

PWRSEL(L)

Input Low Threshold

0.4

EN(H)

Input High Threshold

1.6

EN(L)

Input Low Threshold

0.4

STAT

Output Low Voltage

STAT Pin Sinks 4mA

0.4

STAT

STAT Pin Current Sink Capability

8.0

OVP

Over-Voltage Protection Threshold

4.4

Pre-Charge Current I

CHG

For SETH Mode

For SETL Mode

Charge Termination Threshold Current

For SETH Mode

7.5

TERM

CHG

Charge Termination Threshold Current

For SETL Mode

TERM

CHG

Current Source from TS Pin

µA

TS1

TS Hot Temperature Fault

Threshold 310 330

350

Hysteresis

TS2

TS Cold Temperature Fault

Threshold 2.2

2.3

2.4

Hysteresis

I_DATA

DATA Pin Sink Current

DATA Pin is Active Low State

3.0

DATA(H)

Input High Threshold

1.6

DATA)(L)

Input Low Threshold

0.4

PULSE

Status Request Pulse Width

Status Request

200

PERIOD

System Clock Period

µs

DATA

Data Output Frequency

kHz

OVSD

Over-Temperature Shutdown Threshold

145

°C

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

1. The AAT3685 output charge voltage is specified over the 0° to 70°C ambient temperature range; operation over the -25°C to +85°C

temperature range is guaranteed by design.

Typical Characteristics

Preconditioning Charge Current vs. Temperature

(SETH; SETH = 3.83k

)

Temperature (

°C)

(mA)

100

110

120

-50

-25

100

Preconditioning Threshold

Voltage vs. Temperature

Temperature (

MIN

(V)

2.95

2.96

2.97

2.98

2.99

3.00

3.01

3.02

3.03

3.04

3.05

-50

-25

100

End of Charge Voltage vs. Temperature

Temperature (

BAT

(V)

4.158

4.179

4.200

4.221

4.242

-50

-25

100

Recharge Voltage vs. Temperature

Temperature (

RCH

(V)

4.040

4.050

4.060

4.070

4.080

4.090

4.100

4.110

4.120

4.130

4.140

-50

-25

100

Battery Voltage vs. Supply Voltage

Supply Voltage (V)

BAT

(V)

4.158

4.179

4.200

4.221

4.242

4.5

4.75

5.25

5.5

FASTCHARGE

vs. R

SET

)

FASTCHARGE

(mA)

100

1000

10000

100

1000

SETL

SETH

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Typical Characteristics

Fast Charge Current vs. Supply Voltage

(SETH; SETH = 3.83k

)

Supply Voltage (V)

(mA)

200

400

600

800

1000

1200

4.40

4.50

4.60

4.70

4.80

4.90

5.00

°C

Fast Charge Current vs. Supply Voltage

(SETL; SETL = 40.2k

)

Supply Voltage (V)

(mA)

100

120

4.5

5.5

6.5

BAT

= 3.3V

BAT

= 3.5V

BAT

= 3.9V

Fast Charge Current vs. Supply Voltage

(SETH; SETH = 3.83k

)

Supply Voltage (V)

(mA)

200

400

600

800

1000

1200

4.25

4.5

4.75

5.25

5.5

5.75

BAT

= 3.3V

BAT

= 3.9V

BAT

= 3.5V

Charging Current vs. Battery Voltage

(SETL; SETL = 40.2k

)

Battery Voltage (V)

(mA)

100

120

2.5

3.5

4.5

Charging Current vs. Battery Voltage

(SETH; SETH = 3.83k

)

Battery Voltage (V)

(mA)

200

400

600

800

1000

1200

2.5

3.5

4.5

Fast Charge Current vs. Temperature

(SETH; SETH = 3.83k

)

Temperature (

°C)

(mA)

900

920

940

960

980

1000

1020

1040

1060

1080

1100

-50

-25

100

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Typical Characteristics

Charge Current vs. Time

(SETH; SETH = 3.83k

)

Time (sec)

BUS

(400mV/div)

Charge

Current

(400mA/div)

Peripheral

Current

Consumption

(400mA/div)

Charge Reduction

Mode Activated

Supply Current vs. SETH Resistor

SETH Resistor (k

)

(mA)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

100

1000

Constant Current

Pre-Conditioning

vs. Supply Voltage

PWRSEL (Falling)

Supply Voltage (V)

(V)

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

4.2

4.4

4.6

4.8

5.2

5.4

5.6

5.8

-40

°C

+25

°C

+85

°C

vs. Supply Voltage

PWRSEL (Rising)

Supply Voltage (V)

(V)

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

4.2

4.4

4.6

4.8

5.2

5.4

5.6

5.8

-40

°C

+25

°C

+85

°C

vs. Supply Voltage

EN Pin (Falling)

Supply Voltage (V)

(V)

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

4.2

4.4

4.6

4.8

5.2

5.4

5.6

5.8

-40

°C

+25

°C

+85

°C

vs. Supply Voltage

EN Pin (Rising)

Supply Voltage (V)

(V)

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

4.2

4.4

4.6

4.8

5.2

5.4

5.6

5.8

-40

°C

+25

°C

+85

°C

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Functional Block Diagram

Charge

Control

Current

Compare

Reverse Blocking

CV/

Precharge

ADP/USB

PWRSEL

Constant

Current

BAT

UVLO

Over-

Temperature

Protect

Charge

Status

STAT2

STAT1

Window

Comparator

80µA

SETH

SETL

Serial

Data

DATA

GND

Charge

Reduction

Loop

CHR

IC enable

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Functional Description

The AAT3685 is a highly integrated single cell lithi-

um-ion/polymer battery charger IC designed to

operate from adapter or USB port V

BUS

supplies,

while requiring a minimum number of external

components. The device precisely regulates bat-

tery charge voltage and current for 4.2V lithium-

ion/polymer battery cells.
The AAT3685 is specifically designed for being

powered from a USB port V

BUS

supply, but it can

also be powered from any input voltage source

capable supplying 4.5V to 5.5V for loads up to 1A.

The AAT3685 constant charge current can be

externally programmed for two levels, SETH and

SETL, for maximum constant current charge levels

up to 1A. The SETH/L mode has an automatic

Charge Reduction Loop control to allow users to

charge the battery with limited available current

from a port while maintaining the regulated port

voltage. This system assures the battery charge

function will not overload the port while charging if

other system demands also share power with the

respective port supply.
Status monitor output pins are provided to indicate

the battery charge status by directly driving two

external LEDs. A serial interface output is available

to report 14 various charge states to a system

microcontroller.
Battery temperature and charge state are fully

monitored for fault conditions. In the event of an

over-voltage or over-temperature failure, the

device will automatically shut down, thus protecting

the charging device, control system, and the bat-

tery under charge. In addition to internal charge

controller thermal protection, the AAT3685 also

provides a temperature sense feedback function

(TS pin) from the battery to shut down the device in

the event the battery exceeds its own thermal limit

during charging. All fault events are reported to the

user either by the simple status LEDs or via the

DATA pin function.

Charging Operation

The AAT3685 has four basic modes for the battery

charge cycle and is powered from the input: pre-con-

ditioning/trickle charge; constant current/fast charge;

constant voltage; and end of charge. For reference,

Figure 1 shows the current versus voltage profile

during charging phases.

Battery Preconditioning

Before the start of charging, the AAT3685 checks

several conditions in order to assure a safe charging

environment. The input supply must be above the

minimum operating voltage, or under-voltage lockout

threshold (V

UVLO

), for the charging sequence to

begin. In addition, the cell temperature, as reported

by a thermistor connected to the TS pin from the bat-

tery, must be within the proper window for safe

charging. When these conditions have been met and

a battery is connected to the BAT pin, the AAT3685

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

below the Preconditioning Voltage Threshold (V

MIN

the AAT3685 begins preconditioning the cell.
The battery preconditioning trickle charge current

is equal to the fast charge constant current divided

by 10. For example, if the programmed fast charge

current is 500mA, then the preconditioning mode

(trickle charge) current will be 50mA. Cell precon-

ditioning is a safety precaution for a deeply dis-

charged battery and also aids in limiting power dis-

sipation in the pass transistor when the voltage

across the device is at the greatest potential.

Fast Charge / Constant Current Charging

Battery cell preconditioning continues until the volt-

age on the BAT pin exceeds the Preconditioning

Voltage Threshold (V

MIN

). At this point, the AAT3685

begins the constant current fast charging phase.

The fast charge constant current (I

) amplitude is

determined by the selected charge mode SETH or

SETL and is programmed by the user via the R

SETH

and R

SETL

resistors. The AAT3685 remains in con-

stant current charge mode until the battery reaches

the voltage regulation point, V

BAT

Constant Voltage Charging

The system transitions to a constant voltage charg-

ing mode when the battery voltage reaches output

charge regulation threshold (V

BAT

) during the con-

stant current, fast charge phase. The regulation

voltage level is factory programmed to 4.2V ( 1%).

The charge current in the constant voltage mode

drops as the battery cell under charge reaches its

maximum capacity.

End of Charge Cycle Termination and Recharge
Sequence

When the charge current drops to 7.5% of the pro-

grammed fast charge current level in the constant volt-

age mode, the device terminates charging and goes

into a sleep state. The charger will remain in a sleep

state until the battery voltage decreases to a level

below the battery recharge voltage threshold (V

RCH

When the input supply is disconnected, the charg-

er will also automatically enter power-saving sleep

mode. Only consuming an ultra-low 0.3µA in sleep

mode, the AAT3685 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 AAT3685 input volt-

age drops, the device will enter the sleep mode and

automatically resume charging once the input sup-

ply has recovered from its fault condition.

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Figure 1: Current vs. Voltage Profile During Charging Phases.

Constant Current

Charge Phase

Constant Voltage

Charge Phase

Preconditioning

Trickle Charge

Phase

Charge Complete Voltage

Constant Current Mode

Voltage Threshold

Regulated Current

Trickle Charge and

Termination Threshold

I = CC / 10

I = Max CC

System Operation Flow Chart

UVLO

Battery

Temperature Monitor

TS1

< TS < V

TS2

Preconditioning Test

Current Phase Test

> V

BAT

MIN

> V

BAT

Voltage Phase Test

> V

UVLO

Shut Down

Mode

Shut Down

Mode

Yes

Low Current

Conditioning

Charge

Low Current

Conditioning

Charge

Battery

Temp. Fault

Battery

Temperature

Fault

Current

Charging

Mode

Current

Charging

Mode

Yes

Voltage

Charging

Mode

Voltage

Charging

Mode

BAT

> I

MIN

Yes

Switch

Yes

Input Detect

PWRSEL > 0

Charge

Completed

Charge

Completed

Recharge Test

RCH

> V

BAT

Yes

Power On

Reset

Power On

Reset

Sleep

Mode

Sleep

Mode

Yes

USB High

Current Loop

SETH

Current Loop

USB Low

Current Loop

SETL

Current Loop

Yes

Fault

Conditions Monitor

OV, OT

Yes

Port Voltage Test

< 4.5V

USB Voltage

Regulation

Enable

Input Voltage

Regulation

Enable

USB Loop

Current

Reduction in USB

Charging Mode

Charge

Current

Reduction

USB Power

Input Power

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Application Information

USB System Power Charging

The USB charge mode provides two programma-

ble fast charge levels up to 1A for each, SETH and

SETL. The SETH or SETL modes may be exter-

nally selected by the select pin (PWRSEL). When

the PWRSEL pin is connected 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 R

SETH

and R

SETL

. Refer to

Table 1 for recommended R

SETH

and R

SETL

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 (V

ADP/USB_CHR

), which is typical-

ly 4.5V. Regardless of which charge function is

selected (SETH or SETL), the charge reduction

system will reduce the fast charge current level in a

linear fashion until the voltage sensed on the input

recovers above the charge reduction threshold volt-

age. The charge reduction threshold (V

ADP/USB_CHR

)

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

placing a resistor divider network between V

ADP/USB

and ground with the center connected to the CHR

pin. The charge reduction feature may be disabled

by connecting a 10k 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:

where R11/R12 << 1M.

ADP/USB_CHR

= 2.0V

R12

R12 + R11

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Table 1: Recommended R

SET

Values.

Figure 2: Internal Equivalent

Circuit for the CHR Pin.

1.025M

825k

R11

R12

CHR

= 2.0V

ADP/USB

CHR

SETH

SETL

SETH

SETL

SET

) R

SET

)

SET

)

SET

)

86.6

500

8.06

57.6

600

6.65

100

42.2

700

5.62

200

21.0

20.5

800

4.87

300

13.7

900

4.32

400

10.2

1000

3.83

Input Charge Inhibit and Resume

The AAT3685 UVLO and power on reset feature

will function when the input pin voltage level drops

below the UVLO threshold. At this point, the charg-

er will suspend charging and shut down. When

power is re-applied to the ADP/USB pin or the

UVLO condition recovers, the system charge con-

trol will assess the state of charge on the battery

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 cur-

rent to 500mA due to the limitations of a USB port

as a power source. The AAT3685 is capable of,

and may be programmed 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 within the operat-

ing voltage limits as specified in the Electrical

Characteristics section of this datasheet. This

makes the AAT3685 perfect for applications that

only have one input path, but may access either a

line adapter source or a USB port supply.
In order to fully utilize the power capacity from a line

adapter or USB port supply, program the SETH

charge rate according to the highest charging cur-

rent capacity of the two possible sources, providing

that neither supply exceeds 1A. A lower charge

level may be set with the SETL charge rate and

selection of the higher or lower charge rate is con-

trolled via the PWRSEL function. If the pro-

grammed charge rate is greater than the current

source capacity, there is little danger of system fail-

ure because the AAT3685 charge reduction loop

will activate to automatically reduce the charging

current and maintain a supply voltage set by the

CHR threshold. If the input supply is incapable of

maintaining an input voltage greater than the under-

voltage lockout level of the AAT3685, the charge

control will suspend charging until the source sup-

ply is capable of supplying the minimum input cur-

rent to charge. At this point, the AAT3685 will auto-

matically resume charging in the appropriate mode

based on the battery cell voltage. In case of an

over-temperature condition with a high charge cur-

rent and large input-to-battery voltage difference,

the device will cycle from charging to thermal shut-

down and re-charge after temperature drops suffi-

ciently, until the battery is charged to 4.2V.

Enable / Disable

The AAT3685 provides an enable function to con-

trol the charger IC on and off. The enable (EN) pin

is an active high. When pulled to a logic low level,

the AAT3685 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

automatically reset and resume charging functions

with the appropriate charging mode based on the

battery charge state and measured cell voltage.

Programming Charge Current

The fast charge constant current charge level for the

ADP/USB input is programmed with set resistors

placed between the SETH and SETL pins and

ground. The accuracy of the fast charge, as well as

the preconditioning trickle charge current, is domi-

nated by the tolerance of the set resistors used. For

this reason, 1% tolerance metal film resistors are

recommended for programming the desired con-

stant current level.
The fast charge constant current charge control

provides for two current set levels, SETH and

SETL. The PWRSEL pin is used to select the high

or low charge current levels. When the PWRSEL

pin is pulled to a voltage level above the V

PWRSEL(H)

threshold, the SETH current level will be selected.

Conversely, this pin should be pulled below the

PWRSEL(L)

to enable the SETL charge level. These

two charge levels may be set to any level between

50mA and 1A, depending upon the system design

requirements for a given charge application. Refer

to Table 1 and Figure 3 for recommended R

SETH

and R

SETL

values.

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Figure 3: I

FASTCHARGE

vs. R

SET

Protection Circuitry

Over-Voltage Protection

An over-voltage event is defined as a condition

where the voltage on the BAT pin exceeds the

maximum battery charge voltage and is set by the

over-voltage protection threshold (V

OVP

). If an

over-voltage condition occurs, the AAT3685 charge

control will shut down the device until voltage on

the BAT pin drops below the over-voltage protec-

tion threshold (V

OVP

). The AAT3685 will resume

normal charging operation after the over-voltage

condition is removed. During an over-voltage

event, the STAT LEDs will report a system fault; the

actual fault condition may also be read via the

DATA pin signal.

Over-Temperature Shutdown

The AAT3685 has a thermal protection control cir-

cuit which will shut down charging functions should

the internal die temperature exceed the preset

thermal limit threshold.

Battery Temperature Fault Monitoring

In the event of a battery over-temperature condi-

tion, the charge control will turn off the internal pass

device and report a battery temperature fault on the

DATA pin function. The STAT LEDs will also dis-

play a system fault. After the system recovers

from a temperature fault, the device will resume

charging operation.

The AAT3685 checks battery temperature before

starting the charge cycle, as well as during all

stages of charging. This is accomplished by moni-

toring the voltage at the TS pin. This system is

intended for use negative temperature coefficient

(NTC) thermistors which are typically integrated into

the battery package. Most commonly used NTC

thermistors used in battery packs are approximate-

ly 10k at room temperature (25°C). The TS pin

has been specifically designed to source 80µA of

current to the thermistor. The voltage on the TS pin

that results from the resistive load should stay with-

in a window from 335mV to 2.32V. If the battery

becomes too hot during charging due to an internal

fault, the thermistor will heat up and reduce in value,

thus pulling the TS pin voltage lower than the TS1

threshold, and the AAT3685 will halt charging and

signal the fault condition. If the use of the TS pin

function is not required by the system, it should be

terminated to ground using a 10k resistor.

Battery Charge Status Indication

The AAT3685 indicates the status of the battery

under charge with two different systems. First, the

device has two status LED driver outputs. These

two LEDs can indicate simple functions such as no

battery charge activity, battery charging, charge

complete, and charge fault. The AAT3685 also

provides a bi-directional data reporting function so

that a system microcontroller may interrogate the

DATA pin and read any one of 14 system states.

Status Indicator Display

Simple system charging status may be displayed

using one or two LEDs in conjunction with the

STAT1 and STAT2 pins on the AAT3685. These

two pins are simple switches to connect the display

LED cathodes to ground. It is not necessary to use

both display LEDs if a user simply wants to have a

single lamp to show "charging" or "not charging."
This can be accomplished by just using the STAT1

pin and a single LED. Using two LEDs and both

STAT pins simply gives the user more information

for charging states. Refer to Table 2 for LED dis-

play definitions.

SET

)

FASTCHARGE

(mA)

100

1000

10000

100

1000

SETL

SETH

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

The LED anodes should be connected to V

USB

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:

Example:

Note: Red LED forward voltage (V

) is typically

2.0V @ 2mA.
Table 2 shows the four status LED display conditions.

Digital Charge Status Reporting

The AAT3685 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 V

USB

. 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 1.5k resis-

tor is recommended when pulling the DATA pin

high to 5.0V at the V

USB

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:

PULL-UP

3mA

(5.0V - 2.0V)

B(STAT1)

= 1.5k

2mA

USB

F(LED)

)

B(STAT1/2)

LED(STAT1/2)

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Table 2: LED Display Status Conditions.

Event Description

STAT1

STAT2

Charge Disabled or Low Supply

Off

Charge Enabled Without Battery

Flash

Battery Charging

Off

Charge Completed

Off

Fault

1. Flashing rate depends on output capacitance.

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Table 3: Serial Data Report Table.

Figure 4: Data Pin Application Circuit.

AAT3685

Status

Control

1.8V to 5.0V

DATA Pin

PULL_UP

µP GPIO

Port

GPIO

OUT

DATA Report Status

Chip Over-Temperature Shutdown

Battery Temperature Fault

Over-Voltage Turn Off

Not Used

SETH Battery Condition Mode

SETH Charge Reduction in Constant Current Mode

SETH Constant Current Mode

SETH Constant Voltage Mode

SETH End of Charging

SETL Battery Condition Mode

SETL Charge End of Charging Reduction in Constant Current Mode

SETL Constant Current Mode

SETL Constant Voltage Mode

SETL End of Charging

Data Report Error

Data Timing

The system microcontroller should assert an active

low data request pulse for minimum duration of

200ns; this is specified by T

LO(DATA)

. Upon sensing

the rising edge of the end of the data request pulse,

the AAT3685 status data control will reply the data

word back to the system microcontroller after a

delay specified by the data report time specification

DATA(RPT)

. The period of the following group of data

pulses will be specified by the T

DATA

specification.

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

Timing Diagram

PULSE

Data

System Reset
System Start

SYNC

LAT

N=1

N=2

N=3

OFF

DATA(RPT)

= T

SYNC

+ T

LAT

< 2.5 P

DATA

OFF

> 2 P

DATA

Thermal Considerations

The AAT3685 is packaged in a Pb-free, 3x3mm

TDFN package which can provide up to 2.0W of

power dissipation when it is properly bonded to a

printed circuit board and has a maximum thermal

resistance of 50°C/W. Many considerations should

be taken into account when designing the printed

circuit board layout, as well as the placement of the

charger IC package in proximity to other heat gen-

erating devices in a given application design. The

ambient temperature around the charger IC will

also have an affect on the thermal limits of a bat-

tery charging application. The maximum limits that

can be expected for a given ambient condition can

be estimated by the following discussion.
First, the maximum power dissipation for a given

situation should be calculated:

Eq. 4:

Where:
P

= Total Power Dissipation by the Device

= Input Voltage Level, V

ADP/USB

BAT

= Battery Voltage as Seen at the BAT Pin

= Maximum Constant Fast Charge Current

Programmed for the Application

= Quiescent Current Consumed by the

Charger IC for Normal Operation

Next, the maximum operating ambient temperature

for a given application can be estimated based on

the thermal resistance of the 3x3mm TDFN pack-

age when sufficiently mounted to a PCB layout and

the internal thermal loop temperature threshold.

Eq. 5:

= T

- (

· P

)

= [(V

- V

BAT

)

· I

+ (V

· I

)]

Where:
T

= Ambient Temperature in Degrees C

= Maximum Device Junction Temperature

Protected by the Thermal Limit Control

= Total Power Dissipation by the Device

= Package Thermal Resistance in °C/W

Example:
For an application where the fast charge current is

set to 500mA, V

USB

= 5.0V and the worst case bat-

tery voltage at 3.0V, what is the maximum ambient

temperature at which the thermal limiting will

become active?
Given:
V

ADP

= 5.0V

BAT

= 3.0V

= 500mA

= 0.75mA

= 140°C

= 50°C/W

Using Equation 4, calculate the device power dissi-

pation for the stated condition:

Eq. 6:

The maximum ambient temperature before the

AAT3685 thermal limit protection will shut down

charging can now be calculated using Equation 5:

Eq. 7:

Therefore, under the stated conditions for this

worst case power dissipation example, the

AAT3685 will suspend charging operations when

the ambient operating temperature rises above

89.81°C.

Capacitor Selection

Input Capacitor

In general, it is good design practice to place a

decoupling capacitor between the ADP/USB pin

and ground. An input capacitor in the range of 1µF

to 22µF is recommended. If the source supply is

unregulated, it may be necessary to increase the

capacitance to keep the input voltage above the

under-voltage lockout threshold during device

enable and when battery charging is initiated.
If the AAT3685 input is to be used in a system with

an external power supply source rather than a USB

port V

BUS

, such as a typical AC-to-DC wall adapter,

then a C

capacitor in the range of 10µF should be

used. A larger input capacitor in this application will

minimize switching or power bounce effects when

the power supply is "hot plugged" in. Likewise, a

10µF or greater input capacitor is recommended

for the USB input to help buffer the effects of USB

source power switching noise and input cable

impedance.

Output Capacitor

The AAT3685 only requires a 1µF ceramic capaci-

tor on the BAT pin to maintain circuit stability. This

value should be increased to 10µF or more if the

battery connection is made any distance from the

charger output. If the AAT3685 is to be used in

applications where the battery can be removed

from the charger, such as in the case of desktop

charging cradles, an output capacitor greater than

10µF may be required to prevent the device from

cycling on and off when no battery is present.

Printed Circuit Board Layout

Considerations

For the best results, it is recommended to physi-

cally place the battery pack as close as possible

to the AAT3685 BAT pin. To minimize voltage

drops on the PCB, keep the high current carrying

traces adequately wide. For maximum power dis-

sipation of the AAT3685 3x3mm TDFN package,

the metal substrate should be solder bonded to

the board. It is also recommended to maximize

the substrate contact to the PCB ground plane

layer to further increase local heat dissipation.

Refer to the AAT3685 evaluation board for a good

layout example (see Figures 5 and 6).

= 140

°C - (50°C/W · 1.00375W)

= 89.81

°C

= (5.0V - 3.0V)

(500mA) + (5.0V

· 0.75mA)

= 1.00375W

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

AAT3685 Evaluation Board Bill of Materials (BOM)

Quantity Description

Desig.

Footprint

Manufacturer

Part Number

Test Pin

DATA

PAD

Mill-Max

6821-0-0001-00-00-08-0

Connecting Terminal Block, USB,GND

TBLOK2

Phoenix Contact 277-1274-ND

2.54mm, 2 Pos

Connecting Terminal Block, BAT, GND, TS

TBLOK3

Phoenix Contact 277-1273-ND

2.54mm, 3 Pos

USB 2.0 Receptacle, 5 Pos

USB

USB-MINI-B

Hirose Electronic H2959CT-ND
Co. Ltd.

Capacitor, Ceramic, 10µF

C1, C2

0805

MuRata

490-1717-1-ND

6.3V 10% X5R 0805

Typical Red LED, Super

1206LED

Chicago Miniature CMD15-21SRC/TR8

Bright

Lamp

Typical Green LED

1206LED

Chicago Miniature CMD15-21VGC/TR8
Lamp

Header, 3-Pin

J1, J2

HEADER2MM-3 Sullins

6821-0-0001-00-00-08-0

Resistor, 10k 1/16W 5%

0603

Panasonic/ECG

P10KCFCT-ND

0603 SMD

Resistor, 4.99k 1/16W R5,

0603

Panasonic/ECG

P4.99KHTR-ND

1% 0603 SMD

Resistor, 40.2k 1/16W

0603

Panasonic/ECG

P40.2KHTR-ND

1% 0603 SMD

Resistor, 8.06k 1/16W R8

0603

Panasonic/ECG

P8.06KHCT-ND

1% 0603 SMD

Resistor, 1k 1/16W 5%

0603

Panasonic/ECG

P1.0KCGCT-ND

0603 SMD

Switch Tact 6mm SPST

SW1

SWITCH

ITT Industries/

CKN9012-ND

H = 5.0mm

C&K Div.

AAT3685 Lithium-Ion/

TDFN33-12

AnalogicTech

AAT3685IWP

Polymer Battery Charger

Ordering Information

Package Information

All dimensions in millimeters.

Top View

Bottom View

Detail "B"

Detail "A"

Side View

3.00 ± 0.05

Index Area

(D/2 x E/2)

Detail "A"

Detail "B"

1.70 ± 0.05

3.00

±
0.05

0.05 ± 0.05

0.229

±
0.051

7.5° ± 7.5°

2.40

±
0.05

0.16

Pin 1 Indicator

(optional)

0.375 ± 0.125

0.3 ± 0.10

0.45

±
0.05

0.23

±
0.05

0.075 ± 0.075

0.1 REF

0.8

+
0.05 -0.20

Option A:

C0.30 (4x) max

Chamfered corner

Option B:

R0.30 (4x) max

Round corner

All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.

Package

Marking

Part Number (Tape and Reel)

TDFN33-12

RNXYY

AAT3685IWP-4.2-T1

AAT3685

Lithium-Ion/Polymer Battery Charger

3685.2006.02.1.2

1. XYY = assembly and date code.

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

BOLD

Advanced Analogic Technologies, Inc.

830 E. Arques Avenue, Sunnyvale, CA 94085

Phone (408) 737-4600

Fax (408) 737-4611

AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights,

or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice.

Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold

subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech

warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. Testing and other quality con-

trol 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.

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