LTC4081

1

4081f

■

Wireless Headsets

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Bluetooth Applications

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Portable MP3 Players

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Multifunction Wristwatches

Li-Ion Battery Charger with 1.8V Buck Regulator

500mA Li-Ion Charger

with NTC Input and

300mA Synchronous Buck

The LTC4081 is a complete constant-current/constant-

voltage linear battery charger for a single-cell 4.2V

lithium-ion/polymer battery with an integrated 300mA

synchronous buck converter. A 3mm × 3mm DFN pack-

age and low external component count make the LTC4081

especially suitable for portable applications. Furthermore,

the LTC4081 is specifically designed to work within USB

power specifications.

The ⎯C⎯H⎯R⎯G pin indicates when charge current has

dropped to ten percent of its programmed value (C/10).

An internal 4.5 hour timer terminates the charge cycle.

The full-featured LTC4081 battery charger also includes

trickle charge, automatic recharge, soft-start (to limit inrush

current) and an NTC thermistor input used to monitor

battery temperature.

The LTC4081 integrates a synchronous buck converter

that is powered from the BAT pin. It has an adjustable

output voltage and can deliver up to 300mA of load cur-

rent. The buck converter also features low-current high-

efficiency Burst Mode operation that can be selected by

the MODE pin.

The LTC4081 is available in a 10-lead, low profile (0.75

mm) 3mm × 3mm DFN package.

Battery Charger:

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Constant-Current/Constant-Voltage Operation

with Thermal Feedback to Maximize Charge Rate

Without Risk of Overheating

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Internal 4.5 Hour Safety Timer for Termination

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Charge Current Programmable Up to 500mA with

5% Accuracy

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NTC Thermistor Input for Temperature Qualified

Charging

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C/10 Charge Current Detection Output

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5μA Supply Current in Shutdown Mode

Switching Regulator:

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High Efficiency Synchronous Buck Converter

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300mA Output Current (Constant-Frequency Mode)

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2.7V to 4.5V Input Range (Powered from BAT Pin)

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MODE Pin Selects Fixed (2.25MHz) Constant-Frequency

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2μA BAT Current in Shutdown Mode

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10-lead, low profile (0.75 mm) 3mm × 3mm DFN

package

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

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

Burst Mode is a registered trademark of Linear Technology Corporation. All other

trademarks are the property of their respective owners. Protected by U.S. Patents,

including 6522118.

500mA

4.2V

Li-Ion/

POLYMER

BATTERY

4.7

μF

806

Ω

510

Ω

806k

4.7

μF

4081 TA01a

10pF

1M

LTC4081

NTC

EN_CHRG

MODE

SW

FB

PROG

EN_BUCK

CHRG

BAT

100k

100k

(1.8V/300mA)

1O

μH

GND

4.7

μF

(3.75V

TO 5.5V)

+

T

LOAD CURRENT (mA)

0.01

40

60

80

0.1

10

100

1

1000

20

0

100

1

10

100

0.1

0.01

1000

4081 TA01b

L = 10

μH

C = 4.7

μF

EFFICIENCY

(Burst)

POWER LOSS

(Burst)

EFFICIENCY

(PWM)

POWER

LOSS

(PWM)

Buck Efficiency vs Load Current