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LT1769

Constant-Current/

Constant-Voltage 2A Battery

Charger with Input Current Limiting

s

Simple Solution to Charge NiCd, NiMH and Lithium

Rechargeable Batteries—Charging Current

Programmed by Resistors or DAC

s

Adapter Current Limit Allows Maximum Possible

Charging Current During System Use*

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Precision 0.5% Accuracy for Voltage Mode Charging

s

High Efficiency Current Mode PWM with 3A Internal

Switch

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5% Charge Current Accuracy

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Adjustable Undervoltage Lockout

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Automatic Shutdown When AC Adapter is Removed

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Low Reverse Battery Drain Current: 3

µA

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Current Sensing Can Be at Either Terminal of the Battery

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Charging Current Soft Start

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Shutdown Control

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Available in 28-Lead Narrow SSOP Package

The LT

simple, efficient solution to fast charge modern recharge-

able batteries including lithium-ion (Li-Ion), nickel-metal-

hydride (NiMH) and nickel-cadmium (NiCd) that require

constant-current and/or constant-voltage charging. The

internal switch is capable of delivering 2A** DC current

(3A peak current). Charge current can be programmed by

resistors or a DAC to within 5%. With 0.5% reference voltage

accuracy, the LT1769 meets the critical constant-voltage

charging requirement for Li-Ion cells.

A third control loop is provided to regulate the current

drawn from the input AC adapter. This allows simulta-

neous operation of the equipment and battery charging

without overloading the adapter. Charge current is reduced

to keep the adapter current below specified levels.

The LT1769 can charge batteries ranging from 1V to 20V.

Ground sensing of current is not required and the battery’s

negative terminal can be tied directly to ground. A saturat-

ing switch running at 200kHz gives high charging effi-

ciency and small inductor size. A blocking diode is not

required between the chip and the battery because the

chip goes into sleep mode and drains only 3

µA when the

wall adapter is unplugged.

Figure 1. 2A Lithium-Ion Battery Charger

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Chargers for NiCd, NiMH, Lead-Acid, Lithium

Rechargeable Batteries

s

Switching Regulators with Precision Current Limit

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

*US patent number 5,723,970

**See LT1510 for 1.5A charger; see LT1511 for 3A charger

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

SW

BOOST

COMP1

CLN

UV

OVP SENSE

BAT

C1

1

µF

†

ADAPTER

CURRENT SENSE

R7

†

500

Ω

R5

†

UNDERVOLTAGE

LOCKOUT

R6

5k

11V TO 28V

1

µF

15

µF

300

Ω

4.93k

1%

0.33

µF

C2

0.47

µF

200

Ω

1%

200

Ω

1%

L1**

22

µH

D2

1N4148

2nF

10k

0.05

Ω

BATTERY CURRENT

SENSE

R3

390k

0.25%

BATTERY

VOLTAGE SENSE

R4

162k

0.25%

22

µF

TANT

8.4V

Li-Ion

LT1769

NOTE: COMPLETE LITHIUM-ION CHARGER,

*TOKIN OR UNITED CHEMI-CON/MARCON

CERAMIC SURFACE MOUNT

**22

µH SUMIDA CDRH125

INPUT CURRENT LIMIT AND UNDERVOLTAGE LOCKOUT

MBRS130LT3 CAN BE USED

TO MAIN

SYSTEM LOAD

SPIN

D1

††

SS24

GND

CLP

D3

††

SS24

1511 • F01

PROG

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