AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

BatteryManager

Typical Application

SMA

B34DLA

FZT968

AAT3680

C2
1

C3
10

R2
1k

SENSE

0.2

1.9k

BATT+

BATT-

TEMP

RT1

RT2

Battery

Pack

DRV

CSI

VSS

STAT

BAT

T2X

LED1

General Description

The AAT3680 BatteryManager is a member of
AnalogicTech's Total Power Management ICTM
(TPMICTM) product family. This device is a lithium-
ion/polymer battery charge and management IC,
specifically designed for compact portable applica-
tions. The AAT3680 precisely regulates battery
charge voltage and charge current, and is capable
of two trickle charge current levels controlled by
one external pin. Battery charge temperature and
charge state are carefully monitored for fault con-
ditions. In the event of an over-current, short-cir-
cuit, or over-temperature failure, the device will
automatically shut down, protecting the charging
device and the battery under charge. A battery
charge state monitor output pin is provided to indi-
cate the battery charge status through a display
LED. The battery charge status output is a serial
interface which may also be read by a system
microcontroller.

The AAT3680 is available in a Pb-free, 8-pin MSOP
or 12-pin TSOPJW package, specified over the
-20°C to +70°C temperature range.

Features

Input Voltage Range: 4.5V to 7V

1% Accurate Preset Voltages: 4.1V, 4.2V

Low Operation Current, Typically 0.5mA

Programmable Charge Current

Automatic Recharge Sequencing

Battery Temperature Monitoring

Deep Discharge Cell Conditioning

Fast Trickle Charge Option with Thermal
Over-Ride

Full Battery Charge Auto Turn-Off / Sleep Mode

Over-Voltage, Over-Current, and Over-
Temperature Protection

Power On Reset

LED Charge Status Output or System
Microcontroller Serial Interface

Temperature Range: -20°C to +70°C

8-Pin MSOP or 12-Pin TSOPJW Package

Applications

Cellular Phones

Desktop Chargers

Personal Digital Assistants (PDAs)

USB Chargers

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Pin Description

Pin Configuration

TSOPJW-12

MSOP-8

(Top View)

CSI

BAT

T2X

DRV

STAT

VSS

BAT

CSI

N/C

T2X

DRV

VSS

TS
VP
VP
VP
VP
STAT

Pin #

TSOPJW-12

MSOP-8

Symbol

Function

BAT

Battery voltage level sense input.

CSI

Current sense input.

N/A

N/C

Not connected.

T2X

2X battery trickle charge control input. Connect this pin to VSS to
double the battery trickle charge current. Leave this pin floating for
normal trickle charge current (10% of full charge current). To enter
microcontroller fast-read status, pull this pin high during power-up.

DRV

Battery charge control output.

VSS

Common ground connection.

STAT

Battery charge status output. Connect an LED in series with 2.2k

from STAT to VP to monitor battery charge state.

8, 9, 10, 11

Power supply input pin.

Battery temperature sense input.

Absolute Maximum Ratings

=25°C, unless otherwise noted.

Thermal Information

Recommended Operating Conditions

Symbol

Description

Conditions

Min

Typ

Max

Units

Operation Input Voltage

4.5

7.0

DRV

DRV Pin Sink Current

Ambient Temperature Range

-20

°C

Symbol

Description

Value

Units

Maximum Thermal Resistance

TSOPJW-12

120

°C/W

MSOP-8

150

Maximum Power Dissipation

TSOPJW-12

1.0

MSOP-8

833

Symbol

Description

Value

Units

Relative to V

-0.3 to 7.5

CSI

CSI to GND

-0.3 to V

+ 0.3

T2X

T2X to GND

-0.3 to 5.5

BAT

BAT to GND

-0.3 to V

+ 0.3

Operating Junction Temperature Range

-40 to 150

°C

ESD

ESD Rating

Note 2

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

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

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

2. IC devices are inherently ESD sensitive; handling precautions required.
3. Mounted on an FR4 printed circuit board.

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Electrical Characteristics

= 4.5V to 5.5V, T

= -20°C to 70°C, unless otherwise noted; typical values are at T

= 25°C.

Symbol Description

Conditions

Min

Typ

Max Units

Operating Current

= 5.5V, V

= 4.1V, V

= 4.2V

0.5

SLEEP

Sleep Mode Current

= 3.5V, V

= 4.1V, V

= 4.2V

µA

STAT(HI)

STAT High-Level Output

= 5.5V

-1

µA

Leakage Current

STAT(LOW)

STAT Low-Level Sink Current

= 5.5V, I

SINK

= 5mA

0.3

0.6

SINK

DRV Pin Sink Current

= 5.5V

OL@DRV

DRV Pin Output Low

SINK

= 5mA, V

= 5.5V

0.4

1.0

AAT3680-4.1

= 25°C

4.075 4.100

4.125

Output Charge Voltage

See Note 1

4.059 4.100

4.141

AAT3680-4.2

= 25°C

4.175 4.200

4.225

See Note 1

4.158 4.200

4.242

Charge Current Regulation

= 5.5V, V

= 4.1V, V

= 4.2V

100

110

AAT3680-4.1

2.94

3.0

3.06

MIN

Preconditioning Voltage Threshold

AAT3680-4.2

3.04

3.1

3.16

TRICKLE

Trickle-Charge Current Regulation

T2X Floating, V

= 4.1V, V

= 4.2V

Trickle Charge Current Gain

T2X = V

1.8

TS1

Low-Temperature Threshold

= 5.5V

29.1

30.9

% V

TS2

High-Temperature Threshold

= 5.5V

58.2

61.8

% V

TERM

Charge Termination Threshold Voltage

= 4.1V

3.92

4.00

4.08

RCH

Battery Recharge Voltage Threshold

= 4.2V

4.018

4.10

4.182

UVLO

Under-Voltage Lockout

Rising, T

= 25°C

3.5

4.0

4.5

OVP

Over-Voltage Protection Threshold

4.4

OCP

Over-Current Protection Threshold

200

% V

1. The AAT3680 output charge voltage is specified over 0° to 50°C ambient temperature; operation over -20°C to +70°C is guaranteed

by design.

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Functional Block Diagram

LED Signal

Generator

MUX

Microcontroller

Status Generator

Microcontroller

Read Enable

Charge Status

Logic Control

Power-On

Reset

CSI

STAT

T2X

DRV

VSS

Under-

Voltage

Lock Out

Over-Current /

Short-Circuit

Protection

2x Trickle

Charge

Control

Loop Select

MUX Driver

BAT

REF

Temperature Sense

Comparator

Voltage

Comparator

Current Loop

Error Amp

Voltage Loop

Error Amp

Functional Description

The AAT3680 is a linear charge controller designed
for single-cell lithium-ion/polymer batteries. It is a
full-featured battery management system IC with
multiple levels of integrated power savings, system
communication, and protection. Refer to the block
diagram (above) and flow chart (Figure 1) in this
section for details.

Cell Preconditioning

Before the start of charging, the AAT3680 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 (V

UVLO

), for the charging

sequence to begin. Also, the cell temperature, as
reported by a thermistor connected to the TS pin,
must be within the proper window for safe charging.
When these conditions have been met and a bat-
tery is connected to the BAT pin, the AAT3680
checks the state of the battery. If the cell voltage is
below V

MIN

, the AAT3680 begins preconditioning

the cell. This is performed by charging the cell with
10% of the programmed constant current. 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 AAT3680 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 V

If an over-temperature fault is triggered, the fast
trickle charge will be latched off, and the AAT3680
will continue at the default 10% charge current.

Constant Current Charging

Cell preconditioning continues until the voltage on
the BAT pin reaches V

MIN

. At this point, the

AAT3680 begins constant current charging (fast
charging). Current level for this mode is pro-
grammed using a current sense resistor R

SENSE

between the VP and CSI pins. The CSI pin moni-
tors the voltage across R

SENSE

to provide feedback

for the current control loop. The AAT3680 remains
in constant current charge mode until the battery
reaches the voltage regulation point, V

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Constant Voltage Charging

When the battery voltage reaches V

during con-

stant current mode, the AAT3680 transitions to con-
stant voltage mode. The regulation voltage is fac-
tory programmed: 4.1V and 4.2V are available to
support different anode materials in lithium-ion/poly-
mer cells. In constant voltage operation, the
AAT3680 monitors the cell voltage and terminates
the charging cycle when the voltage across R

SENSE

decreases to approximately 10mV.

Charge Cycle Termination, Recharge

Sequence

After the charge cycle is complete, the AAT3680
latches 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 V

RCH

(recharge threshold voltage) or the AAT3680 is reset
by cycling the input supply through the power-on
sequence. Falling below V

RCH

signals the IC that it

is time to initiate a new charge cycle.

Figure 1: AAT3680 Operational Flow Chart.

UVLO

Temperature Test

TS > V

TS1

TS < V

TS2

Power On Reset

Preconditioning Test

Current Phase Test

> V

BAT

MIN

> V

BAT

TERM

SENSE

< V

RCH

Voltage

Phase Test

> V

UVLO

Shut Down

Mode

Shutdown

Mode

Yes

Low Current

Conditioning

Charge

Low Current

Conditioning

Charge

(Trickle Charge)

Temperature

Fault

Temperature

Fault

Current

Charging

Mode

Current

Charging

Mode

Yes

Voltage

Charging

Mode

< I

BAT

Yes

Charge Complete

Latch Off

Charge Complete

Latch Off

Voltage

Charging

Mode

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Sleep Mode

When the input supply is disconnected, the charger
automatically enters power-saving sleep mode. Only
consuming an ultra-low 2µA in sleep mode, the
AAT3680 minimizes battery drain when it is not
charging.This feature is particularly useful in applica-
tions where the input supply level may fall below the
battery charge or under-voltage lockout level. In such
cases, where the AAT3680 input voltage drops, the
device will enter sleep mode and automatically
resume charging once the input supply has recov-
ered from its fault condition. This makes the AAT3680
well suited for USB battery charger applications.

Charge Inhibit

The AAT3680 charging cycle is fully automatic;
however, it is possible to stop the device from
charging even when all conditions are met for
proper charging. Switching the TS pin to either VP
or VSS will force the AAT3680 to turn off the pass
device and wait for a voltage between the low- and
high-temperature voltage thresholds.

Resuming Charge and the V

RCH

Threshold

The AAT3680 will automatically resume charging
under most conditions when a battery charge cycle is
interrupted. Events such as an input supply interrup-
tion or under voltage, removal and replacement of the
battery under charge, or charging a partially drained
battery are all possible. The AAT3680 will monitor the
battery voltage and automatically resume charging in
the appropriate mode based upon the measured bat-
tery cell voltage. This feature is useful for systems
with an unstable input supply, which could be the
case when powering a charger from a USB bus sup-
ply. This feature is also beneficial for charging or
"topping off" partially discharged batteries.

The only restriction on resuming charge of a bat-
tery is that the battery cell voltage must be below
the battery recharge voltage threshold (V

RCH

)

specification. There is V

RCH

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 AAT3680-4.2 has a typical V

RCH

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 V

RCH

threshold.

In another case, a battery 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 V

RCH

threshold and the charge cycle will immediately
resume where it left off.

LED Display

Charge Status Output
The AAT3680 provides a battery charge status output
via the STAT pin. STAT is an open-drain serial data
output capable of displaying five distinct status func-
tions 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 cir-
cuit -OR- when an over-voltage (OV) condition
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
AAT3680 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 out-
put capacitor being used. The LED cycles on for
two periods then remains off for two periods. See
Figure 2.

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

High-Speed Data Reporting

A high-speed data reporting application schematic
is shown in Figure 3. An optional system micro-
controller interface can be enabled by pulling up
the T2X pin to 4.5V to 5.5V during the power-up
sequence. The T2X pin should be pulled high with
the use of a 100k

resistor. If the input supply to

VP will not exceed 5.5V, then the T2X pin may be
tied directly to VP through a 100k

resistor. Since

this is a TTL-level circuit, it may not be pulled high-
er 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 status word 160µs in length
(see Figure 4).

An additional feature is the Output Status for
Battery Not Detected state. When the AAT3680
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 AAT3680
will only trickle charge at the 2X trickle charge
level. This is because the TX2 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 internal to the AAT3680.

Figure 3: High-Speed Data Reporting Application Schematic.

FZT788B

AAT3680

4.7

100k

SENSE

0.2

2.5k

BATT+

BATT-

TEMP

RT1

RT2

Battery

Pack

DRV

CSI

VSS

STAT

BAT

TX2

STAT

0.1

100k

Figure 2: 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

OFF
ON

OFF

on/off

Protection Circuitry

The AAT3680 is a highly integrated battery man-
agement system IC including several protection
features. In addition to battery temperature moni-
toring, the IC constantly monitors for over-current
and over-voltage conditions. If an over-current sit-
uation occurs, the AAT3680 latches off the pass
device to prevent damage to the battery or the sys-
tem, and enters shutdown mode until the over-cur-
rent event is terminated.

An over-voltage 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 voltage thresh-
old. The AAT3680 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 condi-
tion, the IC will turn off the pass device and report
a FAULT signal on the STAT pin. After the system
recovers from a temperature fault, the IC will
resume operation in the 1X trickle charge mode to
prevent damage to the system in the event a defec-
tive battery is placed under charge. Once the bat-
tery voltage rises above the trickle charge to con-
stant current charge threshold, the IC will resume
the constant current mode.

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

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

Figure 5: Typical Charge Profile.

Preconditioning

(Trickle Charge)

Phase

Constant Current

Phase

Constant Voltage

Phase

Output Charge

Voltage (V

)

Preconditioning

Voltage Threshold

MIN

)

Regulation

Current

CHARGE(REG)

)

Trickle Charge

and Termination

Threshold

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Applications Information

Choosing an External Pass Device

(PNP or PMOS)

The AAT3680 is designed to work with either a
PNP transistor or P-channel power MOSFET.
Selecting one or the other requires looking at the
design tradeoffs, including performance versus
cost issues. Refer to the following design guide for
selecting the proper device.

PNP Transistor
In this design example, we will use the following
conditions: V

= 5V (with 10% supply tolerance),

CHARGE(REG)

= 600mA, 4.2V single cell lithium-ion

pack. V

is the input voltage to the AAT3680, and

CHARGE(REG)

is the desired fast-charge current.

1. The first step is to determine the maximum

power dissipation (P

) in the pass transistor.

Worst case is when the input voltage is the high-
est and the battery voltage is the lowest during
fast-charge (this is referred to as V

MIN

, nominal-

ly 3.1V when the AAT3680-4.2 transitions from
trickle charge to constant current mode). In this
equation, V

is the voltage across R

SENSE

2. The next step is to determine which size package

is needed to keep the junction temperature below
its rated value, T

J(MAX)

. Using this value and the

maximum ambient temperature inside the system
T

A(MAX)

, calculate the thermal resistance R

required:

It is recommended to choose a package with a
lower R

than the number calculated above. A

SOT223 package would be an acceptable choice,
as it has an R

of 62.5°C/W when mounted to a

PCB with adequately sized copper pad soldered
to the heat tab.

3. Choose a collector-emitter (V

) voltage rating

greater than the input voltage. In this example,
V

is 5.0V, so a 15V device is acceptable.

4. Choose a transistor with a collector current rating

at least 50% greater than the programmed
I

CHARGE(REG)

value. In this example, we would

select a device with at least a 900mA rating.

5. Calculate the required current gain (

or h

);

> 200:

where I

C(MAX)

is the collector current (which is the

same as I

CHARGE(REG)

), and I

B(MIN)

is the minimum

amount of base current drive shown in Electrical
Characteristics as I

SINK

. Important Note: The cur-

rent gain (

or h

) can vary by a factor of three

over temperature and drops off significantly with
increased collector current. It is critical to select a
transistor with

, at full current and lowest temper-

ature, greater than the

MIN

calculated above.

In summary, select a PNP transistor with ratings
V

15V, R

80°C/W, I

900mA,

MIN

30 in

a SOT223 (or better thermal) package.

P-Channel Power MOSFET
The following conditions apply to Figure 6, for use
with the AAT3680-4.2V version: V

= 5V (with 10%

supply tolerance), I

CHARGE(REG)

= 750mA, 0.4V

Schottky diode, 4.2V single cell lithium-ion battery
pack. V

is the input voltage to the AAT3680, and

CHARGE(REG)

is the desired fast-charge current.

MIN

C(MAX)

B(MIN)

= 30

0.60

0.02

J(MAX)

- T

A(MAX)

)

= 80°C/W

(150

- 40)

1.38

= (V

P(MAX)

- V

MIN

)

CHARGE(REG)

= (5.5V - 0.1V - 3.1V)

600mA

= 1.38W

1. The first step is to determine the maximum power

dissipation (P

) in the pass transistor. Worst case

is when the input voltage is the highest and the
battery voltage is the lowest during fast-charge
(this is referred to as V

MIN

, nominally 3.1V when

the AAT3680-4.2 transitions from trickle charge to
constant current mode). In this equation, V

the voltage across R

SENSE

, and V

is the voltage

across the reverse current blocking diode. Refer
to section below titled Schottky Diode for further
details. Omit the value for V

in the equation

below if the diode is not used.

2. The next step is to determine which size package

is needed to keep the junction temperature below
its rated value, T

J(MAX)

. Using this value, and the

maximum ambient temperature inside the system
T

A(MAX)

, calculate the thermal resistance R

required:

It is recommended to choose a package with a
lower R

than the number calculated above.

A SOT223 package would be an acceptable
choice, as it has an R

of 62.5°C/W when

mounted to a PCB with an adequately sized
copper pad soldered to the heat tab.

3. Choose a drain-source (V

) voltage rating

greater than the input voltage. In this example,
V

is 5.0V, so a 12V device is acceptable.

4. Choose a MOSFET with a drain current rating at

least 50% greater than the programmed
I

CHARGE(REG)

value. In this example, we would

select a device with at least a 1.125A rating.

J(MAX)

- T

A(MAX)

)

= 79°C/W

(150

- 40)

1.4

= (V

P(MAX)

- V

MIN

)

CHARGE(REG)

= (5.5V - 0.1V - 0.4V - 3.1V)

750mA

= 1.4W

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Figure 6: Typical Applications Schematic Using a P-Channel Power MOSFET with the AAT3680-4.2.

RFD10P03L

AAT3680

C2
10

C1
4.7

SENSE

0.2

100k

BATT+

BATT-

TEMP

RT1

RT2

Battery

Pack

DRV

CSI

VSS

STAT

BAT

T2X

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

5. Calculate the required threshold voltage to

deliver I

CHARGE(REG)

where V

is the available gate-to-source voltage

provided by the AAT3680, V

is the voltage

across the sense resistor, V

OL@DRV

is the rated

low voltage at the DRV pin, and V

P(MIN)

is the

worst case input voltage (assuming 10% toler-
ance on the 5V supply). Choose a MOSFET
device with sufficiently low V

GS(TH)

so the device

will conduct the desired I

CHARGE(REG)

6. Calculate the worst case maximum allowable

DS(ON)

at worst case V

voltage:

Select a P-channel power MOSFET with R

DS(ON)

lower than 197m

at V

= -4.3V.

In summary, select a P-channel MOSFET with ratings
V

12V, R

79°C/W and R

DS(ON)

197m

= -4.3V in a SOT223 (or better thermal) package.

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 short-
ened charging time without decreasing the battery
lifespan. This means that the suggested fast
charge rate for a 500mAH battery pack is 500mA.
The current sense resistor, R

SENSE

, programs the

charge current according to the following equation:

Where I

CHARGE(REG)

is the desired typical charge cur-

rent during constant current charge mode. V

-V

CSI

is the voltage across R

SENSE

, shown in the Electrical

Characteristic table as V

. To program a nominal

500mA charge current 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:

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 AAT3680 checks battery temperature before
starting the charge cycle, as well as during all
stages of charging. This is accomplished by mon-
itoring the voltage at the TS pin. Either a negative
temperature coefficient thermistor (NTC) or posi-
tive temperature coefficient thermistor (PTC) can
be used because the AAT3680 checks to see that
the voltage at TS is within a voltage window bound-
ed by V

TS1

and V

TS2

. Please see the equations

below for specifying resistors:

and R

for use with NTC Thermistor

- R

)

) - (7

)

SENSE

= 50mW

(0.1

)

0.2

SENSE

- V

CSI

)

CHARGE(REG)

DS(ON)

P(MIN)

- V

CS(MAX)

- V

BAT(MAX)

)

CHARGE(REG)

= 197m

(4.5V

- 0.11V - 4.242V)

0.75A

= (V

+ V

OL@DRV

) - V

P(MIN)

= (0.1V + 0.1V) - 4.5V

= - 4.3V

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

and R

for use with PTC Thermistor

Where R

is the thermistor's cold temperature

resistance and R

is the thermistor's hot tempera-

ture resistance. See thermistor specifications for
information. To ensure there is no dependence on
the input supply changes, connect the divider
between V

and V

. Disabling the temperature-

monitoring function is achieved by applying a volt-
age between V

TS1

and V

TS2

on the TS pin.

Capacitor Selection

Input Capacitor
In general, it is good design practice to place a
decoupling capacitor between the V

and V

pins.

An input capacitor in the range of 1µF to 10µF is rec-
ommended. If the source supply is unregulated, it
may be necessary to increase the capacitance to
keep the input voltage above the under-voltage lock-
out threshold.

If the AAT3680 is to be used in a system with an
external power supply source, 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.

Output Capacitor
The AAT3680 does not need an output capacitor
for stability of the device itself. However, a capaci-
tor connected between BAT and V

will control the

output voltage when the AAT3680 is powered up
when no battery is connected. The AAT3680 can
become unstable if a high impedance load is
placed across the BAT pin to V

. Such a case is

possible with aging lithium-ion/polymer battery
cells. As cells age through repeated charge and
discharge cycles, the internal impedance can rise
over time. A 10µF or larger output capacitor will
compensate for the adverse effects of a high-

impedance load and assure device stability over all
operating conditions.

Operation Under No-Load Conditions

Under no-load conditions, that is when the
AAT3680 is powered with no battery connected
between the BAT pin and V

, the output capacitor

is charged up very quickly by the trickle charge
control circuit to the BAT pin until the output reach-
es the recharge threshold (V

RCH

). At this point, the

AAT3680 will drop into sleep mode. The output
capacitor will discharge slowly by the capacitor's
own internal leakage until the voltage seen at the
BAT pin drops below the V

RCH

threshold. This

100mV cycle will continue at approximately 3Hz
with a 0.1µF capacitor connected. A larger capaci-
tor 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 estab-
lished by the C

OUT

value.

For desktop charger applications, where it might
not be desirable to have a "charger ready" blinking
LED, a large C

OUT

capacitor in the range of 100µF

or more would prevent the operation of this mode.

Reverse Current Blocking Diode

Bipolar Circuit Application
When using the AAT3680 with a PNP transistor, a
reverse blocking diode is not required because
there is no current path from BAT to V

. However,

it is advisable to still place a blocking diode
between the bipolar transistor collector and the
BAT pin connection to the circuit output. In the
event where the input supply is interrupted or
removed during the constant current or constant
voltage phases of the charging cycle, the battery
under charge will discharge through the circuit
pass transistor, rendering it impossible to turn off.
If the circuit is unable to turn off, the reverse leak-
age will eventually discharge the battery. A block-
ing diode will prevent this undesirable effect.

MOSFET Circuit Application
A reverse blocking diode is generally required for
the circuit shown in Figure 6. For this application,
the blocking diode gives the system protection
from a shorted input, when the AAT3680 is used

- R

)

) - (7

)

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

with a P-channel MOSFET. If there is no other pro-
tection in the system, a shorted input could dis-
charge the battery through the body diode of the
pass MOSFET. If a reverse-blocking diode is
added to the system, a device should be chosen
which can withstand the maximum constant cur-
rent charge current at the maximum system ambi-
ent temperature.

Diode Selection
Typically, a Schottky diode is used in reverse current
blocking applications with the AAT3680. Other
lower cost rectifier type diodes may also be used if
sufficient input power supply headroom is available.

The blocking diode selection should based on mer-
its of the device forward voltage (V

), current rat-

ing, and input supply level versus the maximum
battery charge voltage and cost.

First, determine the minimum diode forward voltage
drop requirement. Refer to the following equation:

Where:
V

IN(MIN)

= Minimum input supply level

BAT(MAX)

Maximum battery charge voltage
required

F(TRAN)

= Pass transistor forward voltage drop

F(DIODE)

= Blocking diode forward voltage

Based on the maximum constant current charge
level set for the system, the next step is to deter-
mine the minimum current rating and power han-
dling capacity for the blocking diode. The constant-
current charge level itself will dictate what the mini-
mum current rating must be for a given blocking
diode. The minimum power handling capacity must
be calculated based on the constant current ampli-
tude and the diode forward voltage (V

Where:
P

D(MIN)

= Minimum power rating for a diode selection

= Diode forward voltage

= Constant current charge level for the

system

Schottky Diodes
Schottky diodes are selected for this application
because they have a low forward voltage drop, typ-
ically between 0.3V and 0.4V. A lower V

permits

a lower voltage drop at the constant current charge
level set by the system; less power will be dissi-
pated in this element of the circuit. Schottky
diodes allow for lower power dissipation, smaller
component package sizes, and greater circuit lay-
out densities.

Rectifier Diodes
Any general-purpose rectifier diode can be used
with the AAT3680 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. V

for a typical silicon rectifier diode is in the

range of 0.7V. A higher V

will place an input sup-

ply voltage requirement for the battery charger sys-
tem. This will also require a higher power rated
diode since the voltage drop at the constant current
charge amplitude will be greater. Refer to the pre-
viously stated equations to calculate the minimum
V

and diode P

for a given application.

PCB Layout

For the best results, it is recommended to physical-
ly place the battery pack as closely as possible to
the AAT3680's BAT pin. To minimize voltage drops
in the PCB, keep the high current carrying traces
adequately wide. For maximum power dissipation
in the pass transistor, it is critical to provide enough
copper to spread the heat. Refer to the AAT3680
demo board PCB layout in Figures 8, 9, and 10.

D(MIN)

IN(MIN)

= V

BAT(MAX)

+ V

F(TRAN)

+ V

F(DIODE)

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

Evaluation Board Bill of Materials

PNP Transistor Example

P-Channel Power MOSFET Example

Designator

Part Type

Footprint

Manufacturer

Part Number

0.2

, 0.5W

1206

IRC

LRC1206-01-R200F

, 5%

1206

Various

RT1

100k

, 5%

0805

Various

RT2

100k

, 5%

0805

Various

, 5%

0805

Various

1µF

1206

MuRata

Header/SW1

2mm, 3 Pos

Sullins

PRPN031PAEN
Select with Starting Jumper

10µF

1206

MuRata

GRM42-6X5R75K10

10µF

1206

MuRata

GRM42-6X5R106K16

100k

, 5%

0805

Various

Li-Ion Charge Controller IC

MSOP-8

AnalogicTech

AAT3680IKS-4.2

Green LED

1206

Various

0.0

Jumper

1.0A Schottky Diode

SMA

Diodes Inc.

B340LA

30V P-Ch MOSFET, 0.2

TO-252

Various

RFD10P03L

Designator

Part Type

Footprint

Manufacturer

Part Number

0.2

, 0.5 Watt

1206

IRC

LRC1206-01-R200F

, 5%

1206

Various

RT1

100k

, 5%

0805

Various

RT2

100k

, 5%

0805

Various

3.9k

, 5%

0805

Various

1µF

1206

MuRata

Header/SW1

2mm, 3 Pos

Sullins

PRPN031PAEN
Select with Starting Jumper

10µF

1206

MuRata

GRM42-6X5R75K10

10µF

1206

MuRata

GRM42-6X5R106K16

Not Populated

Li-Ion Charge Controller IC

MSOP-8

AnalogicTech

AAT3680IKS-4.2-T1

Green LED

1206

Various

1.0A Schottky Diode

SMA

Diodes Inc.

B340LA

0.0

Jumper

PNP Transistor

SOT223

Zetex

F2T968

Ordering Information

Package Information

MSOP-8

All dimensions in millimeters.

PIN 1

1.95 BSC

0.254 BSC

0.155

0.075

0.60

0.20

3.00

0.10

0.95

0.15

0.95 REF

0.85

0.10

3.00

0.10

0.65 BSC

0.30

0.08

0.075

4.90

0.10

GAUGE PLANE

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.

Output Voltage

Package

Marking

Part Number (Tape and Reel)

MSOP-8

4.2V

ESXYY

AAT3680IKS-4.2-T1

TSOPJW-12

4.2V

ESXYY

AAT3680ITP-4.2-T1

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

1. XYY = assembly and date code.
2. Sample stock is generally held on all part numbers listed in BOLD.

TSOPJW-12

All dimensions in millimeters.

0.20 + 0.10

- 0.05

0.055

0.045

0.45

0.15

NOM

° ±

3.00

0.10

2.40

0.10

2.85

0.20

0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC

0.15

0.05

0.9625

0.0375

1.00

+ 0.10

0.065

0.04 REF

0.010

2.75

0.25

AAT3680

Lithium-Ion/Polymer

Linear Battery Charge Controller

3680.2006.03.1.6

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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