1

LT1505

DESCRIPTIO

FEATURES

APPLICATIO S

Constant-Current/Voltage

High Efficiency Battery Charger

Figure 1. Low Dropout 4A Lithium-Ion Battery Charger

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Simple Charging of Li-Ion, NiMH and NiCd Batteries

s

Very High Efficiency: Up to 97%

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Precision 0.5% Charging Voltage Accuracy

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Preset Battery Voltages: 12.3V, 12.6V,

16.4V and 16.8V

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5% Charging Current Accuracy

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Charging Current Programmed by Resistor or DAC

s

0.5V Dropout Voltage, Duty Cycle > 99.5%

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AC Adapter Current Limit* Maximizes Charging Rate

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Flag Indicates Li-Ion Charge Completion

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Auto Shutdown with Adapter Removal

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Only 10

µA Battery Drain When Idle

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Synchronizable Up to 280kHz

The LT

multiple battery chemistries including lithium-ion (Li-Ion),

nickel-metal-hydride (NiMH) and nickel-cadmium (NiCd)

using constant-current or constant-voltage control. Maxi-

mum current can be easily programmed by resistors or a

DAC. The constant-voltage output can be selected for 3 or 4

series Li-Ion cells with 0.5% accuracy.

A third control loop limits the current drawn from the AC

adapter during charging*. This allows simultaneous opera-

tion of the equipment and fast battery charging without over-

loading the AC adapter.

The LT1505 can charge batteries ranging from 2.5V to 20V

with dropout voltage as low as 0.5V. Synchronous

N-channel FETs switching at 200kHz give high efficiency

and allow small inductor size. A diode is not required in

series with the battery because the charger automatically

enters a 10

µA sleep mode when the wall adapter is un-

plugged. A logic output indicates Li-Ion full charge when

current drops to 20% of the programmed value.

The LT1505 is available in a 28-pin SSOP package.

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Notebook Computers

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Portable Instruments

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Chargers for Li-Ion, NiMH, NiCd and Lead Acid

Rechargeable Batteries

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

5

Ω

1

µF

300

Ω

C7

0.68

µF

C6

0.1

µF

C3

2.2

µF

22

µF

25V

×2

C2

0.68

µF

12.6V

BATTERY

NOTE: DBODY IS THE BODY DIODE OF M3

L1: SUMIDA CDRH127-150

(CAN BE FROM 10

µH TO 30µH)

M1

Si4412

M2

Si4412

D4

MBRS140

D2

MMSD4148T1

D3

MMSD4148T1

R7

500

Ω

100k

R5

4k

R1

1k

R6

4k

*BODY DIODE

POLARITY MUST

BE AS SHOWN

0.025

Ω

M3

Si4435

DBODY*

TO

SYSTEM POWER

(FROM

ADAPTER)

0.025

Ω

L1

15

µH

1505 F01

4.93k

1%

0.33

µF

3k

200

Ω

1%

200

Ω

1%

47

µF

35V

C1

1

µF

C4

0.1

µF

BAT2 BAT

SENSE

LT1505

BOOST

BOOSTC

SPIN

PGND

AGND

4.1V

4.2V

3 CELL

PROG

BGATE

COMP1

CAP

FLAG

SHDN

SYNC

UV

INFET

SW

TGATE

GBIAS

CLP

CLN

*US Patent No. 5,723,970