Datasheet LTC1731ES8-4.2, LTC1731-4.2, LTC1731EMS8-4.2 Datasheet (Linear Technology)

FEATURES

Final Electrical Specifications

LTC1731-4.2

Lithium-Ion Linear

Battery Charger Controller

December 1999

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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 8-Pin MSOP Package

■

Automatic Sleep Mode When Input Supply
is Removed (Only 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®1731-4.2 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 4.2V.

When the input supply is removed, the LTC1731-4.2
automatically enters a low current sleep mode, dropping
the battery drain current to 5µA. 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 2.5V.

The LTC1731-4.2 is available in the 8-pin MSOP and SO
packages.

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

TYPICAL APPLICATION

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500mA Li-Ion Charger

V

IN

5V TO 15V

MBRM120T3

1k

2

3

C

TIMER

0.1µF

*SHUTDOWN INVOKED BY FLOATING THE PROG PIN

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.

V

CC

CHRG

LTC1731-4.2

TIMER

GND

7

SENSE

DRV

BAT

PROG

4

8
6

1
5

R

PROG

19.6k

*

R

SENSE

0.2Ω

Q1
Si9430DY

I

BAT

+

Li-ION
CELL

1µF

= 500mA

10µF

1731 TA01

1

LTC1731-4.2

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

LTC1731EMS8-4.2

MS8 PART MARKING

LTKQ

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

LTC1731ES8-4.2

S8 PART MARKING

173142

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 LTC1731-4.2 (5V ≤ VCC ≤ 12V) ● 4.158 4.2 4.242 V
Current Mode Charge Current R

Trickle Charge Current V
Trickle Charge Threshold Voltage From Low to High ● 2.4 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 95 mA

SENSE

● 12 mA

2

LTC1731-4.2

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
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

CC

) Low to High 40 69 100 mV

BAT

● 5.6 V

PROG

≤ 5mV ● 300 µA

PROG

=19.6k 2.457 V
= 1V 70 100 130 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 LTC1731-4.2 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 chip 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 8V (max) below VCC.

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

BAT

is
within 54mV of VCC, the LTC1731-4.2 is forced into sleep
mode, dropping ICC to 7µA. VCC ranges from 4.5V to 12V.
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

LTC1731-4.2

BLOCK DIAGRA

CHRG

2

100µA

TIMER

3

W

C/10 C/10

LOGIC

SHDN SLP

OSCILLATOR

STOP

COUNTER

V

CC

7

R

+

C1

80Ω

–

720Ω

800Ω

LBO

+

C4

–

CA

+

–

–

C2

+

SENSE

+

54mV

–

DRV

BAT

SENSE

8

6

1

BATTERY CURRENT I

C3 A1

= (2.457V • 800Ω)/(R

BAT

V

REF

+

+

–

–

• R

SENSE

)

PROG

V

CC

2.5µA

PROG

5

R

PROG

VA

CHARGE

–

+

V

REF

2.457V

GND

4

1731 BD

4

OPERATIO

LTC1731-4.2

U

The LTC1731-4.2 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
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 shrinks the voltage
drop across R

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 battery voltage is below 2.457V per cell, 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
per cell. In constant-current mode, the charge current is
set by the combination of R

sets a program current through an internal

PROG

SENSE

) from the PROG pin to ground

PROG

) between the VCC and SENSE

SENSE

CC

which sets

SENSE

, thus reducing the charge current.

SENSE

and R

PROG

.

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.

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
LTC1731-4.2 can be turned into a current source by
pulling the TIMER pin to VCC. When in the constant­current 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 5µA. 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.

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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.

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.

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

BAT

CC

Trickle Charge and Defective Battery Detection

At the beginning of the charging sequence, if the battery
voltage is low (below 2.457V per cell) the charger goes
into trickle mode. The charge current is dropped to 10% of
the full-scale 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.

Shutdown

The LTC1731-4.2 can be forced into shutdown by float­ing the PROG pin and allowing the internal 2.5µA current
source to pull the pin above the 2.457V shutdown

5

LTC1731-4.2

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WUU

APPLICATIONS INFORMATION

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.

Programming Charge Current

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

I

= (I

BAT

= (2.457V/R

where R

PROG

ground.
For example, if 0.5A charge current is needed, select a

value for R
charge current. R

R

= (2.457V/500mA)(800Ω/0.2Ω) = 19.656k

PROG

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

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:

PROG

)(800Ω/R

PROG

)

SENSE

)(800Ω/R

SENSE

)

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

+

V

7

V

CC

LTC1731-4.2

CHRG

Figure 1. Microprocessor Interface

100k

2

1k

µPROCESSOR

I/O

I/O

1731 F01

from this pin (charging, C/10 and stop charging). See
Figure 1.

End of Charge (C/10)

The LTC1731-4.2 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 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

Time = (3 Hours)(C

TIMER

/0.1µF)

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 battery 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

Typically the LTC1731-4.2 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 too much
charging 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.

Constant-Current Only Mode

The LTC1731-4.2 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

6

LTC1731-4.2

U

WUU

APPLICATIONS INFORMATION

constant-current only mode, the timer and voltage ampli­fier are both disabled. An external termination method is
required to properly terminate the charge.

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

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TYPICAL APPLICATION

Linear Charger Using a PNP Transistor

C

TIMER

0.1µF

R2
1k

2

3

CHRG

TIMER

7

V

CC

SENSE

LTC1731-4.2

PROG

GND

4

DRV

BAT

C1
1nF

8
6

1
5

R

PROG

19.6k

pin to keep the ripple voltage low when the battery is
disconnected.

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.

V

IN

5V TO 15V

MBRM120T3

R

R1
10k

Q1
2N5087

SENSE

0.2Ω

Q2
ZTX749

I

BAT

+

Li-ION
CELL

= 500mA

C3
1µF

C2
10µF

1731 TA02

PACKAGE DESCRIPTION

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°

(1.346 – 1.752)

0°– 8° TYP

0.016 – 0.050

(0.406 – 1.270)

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Dimensions in inches (millimeters) unless otherwise noted.

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

0.053 – 0.069

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)

8

1

0.189 – 0.197*
(4.801 – 5.004)

7

6

3

2

5

0.150 – 0.157**
(3.810 – 3.988)

SO8 1298

4

7

LTC1731-4.2

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TYPICAL APPLICATION

C

TIMER

0.1µF

PACKAGE DESCRIPTION

Low Dropout Linear Charger

V

IN

4.5V

Q1

PROG

1/2 Si9934DY

R

SENSE

0.2Ω

Q2
1/2 Si9934DY

I

= 500mA

BAT

+

Li-ION
CELL

C1
1µF

C2
10µF

1731 TA03

R1

50k

2

3

V

CC

CHRG

LTC1731-4.2

TIMER

GND

7

SENSE

PROG

4

DRV

BAT

8
6

1
5

R

19.6k

U

Dimensions in inches (millimeters) unless otherwise noted.

MS8 Package

8-Lead Plastic MSOP

(LTC DWG # 05-08-1660)

0.118 ± 0.004*

0.040

± 0.006

SEATING

PLANE

(1.02 ± 0.15)

0.012

(0.30)

0.0256

REF

(0.65)

BSC

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

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

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OUT

OUT

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

1731is, sn1731 LT/TP 1299 4K • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 1999