Datasheet LTC1731-4.1, LTC1731ES8-4.1 Datasheet (Linear Technology)

FEATURES

Final Electrical Specifications

LTC1731-4.1

Lithium-Ion Linear

Battery Charger Controller

April 2000

U

DESCRIPTION

■

Complete Linear Charger Controller for
1-Cell Lithium-Ion Batteries

■

1% Voltage Accuracy

■

Programmable Charge Current

■

C/10 Charge Current Detection Output

■

Programmable Charge Termination Timer

■

Space Saving, Thin 8-Pin MSOP Package

■

Automatic Sleep Mode When Input Supply
is Removed (7µA Battery Drain)

■

Automatic Trickle Charging of Low Voltage Cells

■

Programmable for Constant-Current-Only Mode

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APPLICATIONS

■

Cellular Phones

■

Handheld Computers

■

Charging Docks and Cradles

■

Programmable Current Source

The LTC®1731-4.1 is a complete constant-current/con­stant-voltage linear charge controller for lithium-ion bat­teries. Nickel-cadmium (NiCd) and nickel-metal-hydride
(NiMH) batteries can also be charged with constant
current using external termination. The external sense
resistor sets the charge current with 5% accuracy. An
internal resistor divider and precision reference set the
final float potential with 1% accuracy. The output float
voltage is set internally to 4.1V.

When the input supply is removed, the LTC1731 automati­cally enters a low current sleep mode, dropping the battery
drain current to 7µA typically. An internal comparator
detects the end-of-charge (C/10) condition while a pro­grammable timer, using an external capacitor, sets the
total charge time. Fully discharged cells are automatically
trickle charged at 10% of the programmed current until
cell voltage exceeds 2.457V.

The LTC1731-4.1 is available in the 8-pin MSOP and SO
packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATION

U

500mA Li-Ion Charger

V

IN

5V TO 12V

MBRM120T3

1k

CHARGE

STATUS

C

TIMER

0.1µF

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

2

3

*SHUTDOWN INVOKED BY FLOATING THE PROG PIN

V

CC

CHRG

LTC1731-4.1

TIMER

GND

7

SENSE

DRV

BAT

PROG

4

8
6

1
5

R

19.6k

PROG

*

R

SENSE

0.2Ω

Q1
Si9430DY

= 500mA

I

BAT

+

Li-ION
CELL

1µF

10µF

1731 TA01

1

LTC1731-4.1

WW

W

ABSOLUTE MAXIMUM RATINGS

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(Note 1)

Input Supply Voltage (VCC) ................................... 13.2V

Input Voltage (SENSE, DRV, BAT,

TIMER, PROG) ....................... –0.3V to (VCC + 0.3V)

Output Voltage (CHRG) ......................... –0.3V to 13.2V

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PACKAGE/ORDER INFORMATION

ORDER PART

TOP VIEW

BAT

1

CHRG

2

TIMER

3

GND

4

MS8 PACKAGE

8-LEAD PLASTIC MSOP

T

= 150°C, θJA = 180°C/W

JMAX

8
7
6
5

SENSE
V

CC

DRV
PROG

NUMBER

LTC1731EMS8-4.1

MS8 PART MARKING

LTJK

Operating Temperature Range (Note 2) .....–40° to 85°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)..................300°C

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ORDER PART

NUMBER

LTC1731ES8-4.1

S8 PART MARKING

173141

BAT

CHRG

TIMER

GND

T

JMAX

TOP VIEW

1

2

3

4

S8 PACKAGE

8-LEAD PLASTIC SO

= 150°C, θJA = 125°C/W

8

SENSE
V

7

CC

DRV

6

PROG

5

Consult factory for Industrial and Military grade parts.

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

I

CC

V

BAT

I

BAT

I

TRIKL

V

TRIKL

V

UV

∆V
V

MSD

UV

Input Supply Voltage ● 4.5 12 V
Input Supply Current Charger On, Current Mode ● 13 mA

Shutdown Mode
Sleep Mode (Battery Drain Current) 7 20 µA

Regulated Output Voltage (5V ≤ VCC ≤ 12V) ● 4.059 4.1 4.141 V
Current Mode Charge Current R

Trickle Charge Current V
Trickle Charge Threshold Voltage From Low to High ● 2.35 2.457 2.55 V
VCC Undervoltage Lockout Voltage From Low to High ● 4.1 4.5 V
VCC Undervoltage Lockout Hysteresis 200 mV
Manual Shutdown Threshold Voltage PROG Pin Low to High 2.457 V

= 19.6k, R

PROG

R

= 19.6k, R

PROG

= 97.6k, R

R

PROG

= 2V, R

BAT

PROG Pin High to Low 2.446 V

PROG

= 0.2Ω 465 500 535 mA

SENSE

= 0.2Ω ● 415 585 mA

SENSE

= 0.2Ω 70 100 130 mA

SENSE

= 19.6k, I

TRIKL

= (VCC – V

)/0.2Ω ● 30 50 100 mA

SENSE

● 12 mA

2

LTC1731-4.1

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

ASD

V

DIS

I

PROG

V

PROG

I

CHRG

V

CHRG

I

C/10

t

TIMER

V

CLAMP

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Automatic Shutdown Threshold Voltage (VCC – V

(V

CC

Voltage Mode Disable Threshold Voltage V
PROG Pin Current Internal Pull-Up Current, No R
PROG Pin Load Regulation PROG Pin Source Current, ∆V
PROG Pin Voltage R
CHRG Pin Weak Pull-Down Current V
CHRG Pin Output Low Voltage I
End of Charge Indication Current Level R
TIMER Accuracy C
DRV Pin Clamp Voltage V

TIMER

PROG

CHRG

CHRG

PROG

TIMER

CLAMP

The ● denotes the specifications which apply over the full operating

) High to Low 30 54 90 mV

BAT

– V

) Low to High 40 69 100 mV

BAT

● 5.6 V

PROG

≤ 5mV ● 300 µA

PROG

=19.6k 2.457 V
= 1V 50 100 150 µA

= 5mA 0.6 1.2 V

= 19.6k, R

= 0.1µF10%

= VCC – V

= 0.2Ω ● 25 50 100 mA

SENSE

, I

DRV

= 50µA 6.5 V

DRIVE

Note 2: The LTC1731-4.1 is guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls. Guaranteed I grade parts are
available, consult factory.

2.5 µA

UUU

PIN FUNCTIONS

BAT (Pin 1): Battery Sense Input. A bypass capacitor of at
least 10µF is required to keep the loop stable when the
battery is not connected. A precision internal resistor
divider sets the final float potential on this pin. The resistor
divider is disconnected in sleep mode.

CHRG (Pin 2): Open-Drain Charge Status Output. When
the battery is being charged, the CHRG pin is pulled low by
an internal N-channel MOSFET. When the charge current
drops to 10% of the full-scale current for at least 0.32
seconds, the N-channel MOSFET turns off and a 100µA
current source is connected from the CHRG pin to GND.
When the timer runs out or the input supply is removed,
the current source will be disconnected and the CHRG pin
is forced into a high impedance state.

TIMER (Pin 3): Timer Capacitor and Constant-Voltage
Mode Disable Input Pin. The timer period is set by placing
a capacitor, C
(C

• 3 hours)/(0.1µF). When the TIMER pin is

TIMER

, to GND. The timer period is t

TIMER

TIMER

=

connected to VCC, the constant-voltage mode is disabled
and the charger will operate in constant-current mode
only. Short the TIMER pin to GND to disable the internal
timer function.

GND (Pin 4): Ground.
PROG (Pin 5): Charge Current Program and Shutdown

Input Pin. The charge current is programmed by connect­ing a resistor, R
= (V

• 800Ω)/(R

PROG

to ground. The charge current is I

PROG

PROG

• R

). The IC can be forced

SENSE

BAT

into shutdown by floating the PROG pin and allowing the
internal 2.5µA current source to pull the pin above the

2.457V shutdown threshold voltage.
DRV (Pin 6): Drive Output Pin for the P-Channel MOSFET

or PNP Transistor. The impedance is high at this pin,
therefore, a high gain PNP pass transistor should be used.
The DRV pin is internally clamped to 6.5V below VCC.

VCC (Pin 7): Positive Input Supply Voltage. When V

BAT

is
within 54mV of VCC, the LTC1731 is forced into sleep
mode, dropping ICC to 7µA. VCC ranges from 4.5V to 12V
(LTC1731-4.1). Bypass this pin with a 1µF capacitor.

SENSE (Pin 8): Current Sense Input. A sense resistor,
R

, must be connected from VCC to the SENSE pin.

SENSE

This resistor is chosen using the following equation:

R

SENSE

= (V

• 800Ω)/(R

PROG

PROG

• I

BAT

)

3

LTC1731-4.1

BLOCK DIAGRA

CHRG

2

100µA

TIMER

3

W

C/10 C/10

LOGIC

SHDN SLP

OSCILLATOR

STOP

V

CC

7

R

+

C1

80Ω

–

720Ω

COUNTER

V

REF

800Ω

LBO

+

C4

–

CA

+

–

–

C2

+

–

SENSE

+

54mV

–

DRV

BAT

SENSE

8

6

1

+

+

C3 A1

–

–

BATTERY CURRENT I

= (2.457V • 800Ω)/(R

BAT

PROG

• R

SENSE

)

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OPERATIO

The LTC1731 is a linear battery charger controller. The
charge current is programmed by the combination of a
program resistor (R
and a sense resistor (R
pins. R

sets a program current through an internal

PROG

trimmed 800Ω resistor setting up a voltage drop from V
to the input of the current amplifier (CA). The current
amplifier servos the gate of the external P-channel MOSFET
to force the same voltage drop across R
the charge current. When the potential at the BAT pin
approaches the preset float voltage, the voltage amplifier
(VA) will start sinking current which reduces the voltage
drop across R

SENSE

) from the PROG pin to ground

PROG

) between the VCC and SENSE

SENSE

CC

which sets

SENSE

, thus reducing the charge current.

V

CC

2.5µA

PROG

5

R

PROG

VA

CHARGE

+

V

REF

2.457V

GND

4

1731 BD

Charging begins when the potential at VCC pin rises above
the UVLO level and a program resistor is connected from
the PROG pin to ground. At the beginning of the charge
cycle, if the cell voltage is below 2.457V, the charger goes
into trickle charge mode. The trickle charge current is 10%
of the full-scale current. If the cell voltage stays low for one
quarter of the total charge time, the charge sequence will
be terminated immediately.

The charger goes into the fast charge constant-current
mode after the voltage on the BAT pin rises above 2.457V.
In constant-current mode, the charge current is set by the
combination of R

SENSE

and R

PROG

.

4

OPERATIO

LTC1731-4.1

U

When the battery approaches the final float voltage, the
charge current will begin to decrease. When the current
drops to 10% of the full-scale charge current, an internal
comparator will turn off the pull-down N-channel MOSFET
at the CHRG pin and connect a weak current source to
ground to indicate an end-of-charge (C/10) condition.

An external capacitor on the TIMER pin sets the total
charge time. After a time-out occurs, the charging will be
terminated immediately and the CHRG pin is forced to a
high impedance state. To restart the charge cycle, simply
remove the input voltage and reapply it, or float the PROG
pin momentarily.

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WUU

APPLICATIONS INFORMATION

Charge Termination

The charger is off when any of the following conditions
exist: the voltage at the VCC pin is below 4.1V, the voltage
at the VCC pin is higher than 4.1V but is less than 54mV
above V
be pulled to VCC and the internal resistor divider is discon­nected to reduce the current drain on the battery.

, or the PROG pin is floating. The DRV pin will

BAT

For batteries like lithium-ion that require accurate final
float potential, the internal 2.457V reference, voltage
amplifier and the resistor divider provide regulation with
±1% (max) accuracy. For NiMH and NiCd batteries, the
LTC1731 can be turned into a current source by pulling
the TIMER pin to VCC. When in the constant-current only
mode, the voltage amplifier, timer and the trickle charge
function are all disabled.

When the input voltage is not present, the charger goes
into a sleep mode, dropping ICC to 7µA. This greatly
reduces the current drain on the battery and increases the
standby time. The charger can be shut down by floating the
PROG pin. An internal current source will pull it high and
clamp at 3.5V.

Shutdown

The LTC1731 can be forced into shutdown by floating the
PROG pin thus allowing the internal 2.5µA current source
to pull the pin above the 2.457V shutdown threshold
voltage. The DRV pin will then be pulled up to VCC and
turn off the external P-channel MOSFET. The internal
timer is reset in the shutdown mode.

Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
rises above 4.1V. To prevent oscillation around
VCC = 4.1V, the UVLO circuit has built-in hysteresis.

Trickle Charge and Defective Battery Detection

At the beginning of the charging sequence, if the battery
voltage is low (below 2.457V) the charger goes into trickle
mode. The charge current is dropped to 10% of the full­scale current. If the low cell voltage persists for one
quarter of the total charging time, the battery is considered
defective, the charging will be terminated and the CHRG
pin output is forced to a high impedance state.

CC

Programming Charge Current

The formula for the battery charge current (see Block
Diagram) is:

I

= (I

BAT

= (2.457V/R

where R
ground.

For example, if 0.5A charge current is needed, select a
value for R
charge current. R

For best stability over temperature and time, 1% resistors
are recommended. The closest 1% resistor value is 19.6k.

PROG

R

= (2.457V/500mA)(800Ω/0.2Ω) = 19.656k

PROG

)(800Ω/R

PROG

PROG

is the total resistance from the PROG pin to

that will drop 100mV at the maximum

SENSE

= 0.1V/0.5A = 0.2Ω, then calculate:

SENSE

)

SENSE

)(800Ω/R

SENSE

)

5

LTC1731-4.1

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WUU

APPLICATIONS INFORMATION

Programming the Timer

The programmable timer is used to terminate the charge.
The length of the timer is programmed by an external
capacitor at the TIMER pin. The total charge time is:

Time = (3 Hours)(C

The timer starts when the input voltage greater than 4.1V
is applied and the program resistor is connected to ground.
After a time-out occurs, the CHRG output will turn into a
high impedance state to indicate that the charging has
stopped. Connecting the TIMER pin to VCC disables the
timer and also puts the charger into a constant-current
mode. To only disable the timer function, short the TIMER
pin to GND.

CHRG Status Output Pin

When the charge cycle starts, the CHRG pin is pulled down
to ground by an internal N-channel MOSFET that can drive
an LED. When the charge current drops to 10% of the full­scale current (C/10), the N-channel MOSFET is turned off
and a weak 100µA current source to ground is connected
to the CHRG pin. After a time-out occurs, the pin will go
into a high impedance state. By using two different value
pull-up resistors, a microprocessor can detect three states
from this pin (charging, C/10 and stop charging). See
Figure 1.

+

V

7

V

CC

LTC1731-4.1

CHRG

Figure 1. Microprocessor Interface

TIMER

2

/0.1µF)

100k

1k

V

DD

µPROCESSOR

OUT

IN

1731 F01

and a 100µA current source is connected to the CHRG pin.
By forcing the OUT pin into a high impedance state, the
current source will pull the pin low through the 100k
resistor. When the internal timer has expired, the CHRG
pin will change to high impedance state and the 100k
resistor will then pull the pin high to indicate the charging
has stopped.

End of Charge (C/10)

The LTC1731 includes a comparator to monitor the charge
current to detect an end-of-charge condition. When the
battery current falls below 10% of full scale, the compara­tor trips and turns off the N-channel MOSFET at the CHRG
pin and switches in a 100µA current source to ground.
After an internal time delay of at least 300ms, this state is
then latched. This delay will help prevent false triggering
due to transient currents. The end-of-charge comparator
is disabled in trickle charge mode.

Gate Drive

Typically the LTC1731 controls an external P-channel
MOSFET to supply current to the battery. The DRV pin is
internally clamped to 6.5V below VCC. This feature allows
low voltage P-channel MOSFETs with gate to source
breakdown voltage rated at 8V to be used.

An external PNP transistor can also be used as the pass
transistor instead of the P-channel MOSFET. Due to the
low current gain of the current amplifier (CA), a high gain
Darlington PNP transistor is required to avoid excessive
charge current error. The gain of the current amplifier is
around 0.6µA/mV. For every 1µA of base current, a 1.6mV
of gain error shows up at the inputs of CA. With R

19.6k (100mV across R

), it represents 1.67% of

SENSE

PROG

=

error in charging current.

When the LTC1731 is in charge mode, the CHRG pin is
pulled down by an internal N-channel MOSFET. To detect
this mode, force the digital output pin, OUT, high and
measure the voltage at the CHRG pin. The N-channel
MOSFET will pull the pin low even with a 1k pull-up
resistor. Once the charge current drops to 10% of the full
scale current (C/10), the N-channel MOSFET is turned off

6

Constant-Current Only Mode

The LTC1731 can be used as a programmable current
source by forcing the TIMER pin to VCC. This is particu­larly useful for charging NiMH or NiCd batteries. In the
constant-current only mode, the timer and voltage ampli­fier are both disabled. An external termination method is
required to properly terminate the charge.

LTC1731-4.1

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WUU

APPLICATIONS INFORMATION

Stability

The charger is stable without any compensation when a
P-channel MOSFET is used as the pass transistor.
However, a 10µF capacitor is recommended at the BAT
pin to keep the ripple voltage low when the battery is
disconnected.

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PACKAGE DESCRIPTION

0.007

(0.18)

0.021

± 0.006

(0.53 ± 0.015)

* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,

PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

° – 6° TYP

0

Dimensions in inches (millimeters) unless otherwise noted.

MS8 Package

8-Lead Plastic MSOP

(LTC DWG # 05-08-1660)

0.040

± 0.006

(1.02 ± 0.15)

SEATING

PLANE

0.012

(0.30)

0.0256

REF

(0.65)

BSC

When a PNP transistor is chosen as the pass transistor, a
1000pF capacitor is required from the DRV pin to VCC. This
capacitor is needed to help stablize the voltage loop. A
10µF capacitor at the BAT pin is also recommended when
a battery is not present.

0.118 ± 0.004*

0.034 ± 0.004

(0.86 ± 0.102)

0.006 ± 0.004
(0.15 ± 0.102)

(3.00 ± 0.102)

0.193 ± 0.006
(4.90 ± 0.15)

8

7

12

6

5

0.118 ± 0.004**

4

3

(3.00 ± 0.102)

MSOP (MS8) 1098

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

*

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

**

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

× 45°

0°– 8° TYP

0.016 – 0.050

(0.406 – 1.270)

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

TYP

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

BSC

0.228 – 0.244

(5.791 – 6.197)

0.189 – 0.197*
(4.801 – 5.004)

7

8

1

2

5

6

0.150 – 0.157**
(3.810 – 3.988)

SO8 1298

3

4

7

LTC1731-4.1

U

TYPICAL APPLICATIONS

Linear Charger Using a PNP Transistor

V

IN

5V TO 12V

MBRM120T3

C

TIMER

0.1µF

R5
1k

LED

AVX0603ZC104KATIA

R2
1k

2

3

C5
1µF
CER

C1

0.1µF

CHRG

TIMER

2

3

C1

R1

1nF

R

PROG

19.6k

10k

Q1
2N5087

7

V

CC

SENSE

LTC1731-4.1

PROG

GND

4

DRV

BAT

8
6

1
5

1.5A Single-Cell Battery Charger

C4

0.47µF

8

6

1

R2

4.7Ω

3

V

CHRG

LTC1731-4.1

TIMER

GND
4

CC

7

SENSE

DRV

BAT

PROG

5

R4

18.2k
1%

R

SENSE

0.2Ω

Q2
ZTX749

I

= 500mA

BAT

+

Li-ION
CELL

5

2

TPS2829DBVR

C3
1µF

C2
10µF

1731 TA02

V

4

1-CELL

Li-Ion

BATTERY

= 5V ~ 6V

IN

R3

0.082Ω
1/4W

Q2
Si2305DS

MBRS130LT3

22µF
CDRH6D38-220NC

+
–

D2
MBRS130LT3

D1

+

C2
22µF
CER

C3
100µF

1731 TA03

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173141i LT/TP 0400 4K • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2000

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

, Up to 10A I

OUT

OUT