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LT1513/LT1513-2

TYPICAL APPLICATIONS

Lithium-Ion Battery Charger with

Switchable Charge Current

Many battery chemistries require several constant-current

settings during the charging cycle. The circuit shown in

Figure 8 uses the LT1513-2 to provide switchable 1.35A and

0.13A constant-current modes. The circuit is based on a

standard SEPIC battery charger circuit set to a single

lithium-ion cell charge voltage of 4.1V. The LT1513-2 has IFB

referenced to ground allowing a simple resistor network to

set the charging current values. In constant-current mode,

the IFB error amplifier drives the FB pin, increasing charging

current, until IR4 is balanced by IR5.

CHARGE

FBVOS

()(

) –

There are several ways to control IR5includingDAC,PWMor

resistor network as shown here. If the lithium cell requires

precharging, Q1 is turned on, setting a constant current of

0.13A. When charge voltage is reached, Q1 is turned off,

programming the full charge current of 1.35A. As the cell

voltage approaches 4.1V, the voltage sensing network (R1,

R2) starts driving the VFB pin, changing the LT1513-2 to

constant-voltage mode. As charging current falls, the output

remains in constant-voltage mode for the remainder of the

charging cycle. When charging is complete, the LT1513-2

can be shut down with the S/S pin.

LT1513-2

L1A

CTX10-4

L1B

GND

IFB

1513 F08

VSW

VFB

VIN

S/S

330

Ω

36k

4.7k

0.1

µF

0.22

µF

4.7

µF

MBRS330T3

µF

25V

×2

µF

25V

910

Ω

10k

3.3V

0.25

Ω

78.7k

0.5%

Li-Ion

RECHARGABLE

CELL

GND

34k

0.5%

CHARGE

SHUTDOWN

PRECHARGE

CHARGE

•

Figure 8. Lithium-Ion Battery Charger

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