13

LT1513/LT1513-2

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

referenced to ground allowing a simple resistor network to

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

I

IR

I

R

CHARGE

R

FBVOS

=

()(

) –

5

4

3

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,

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

1513 F08

1

7

6

3

5

2

S/S

R3

330

Ω

R5

36k

R4

4.7k

C5

0.1

µF

4

C4

0.22

µF

C2

4.7

µF

D1

MBRS330T3

C1

22

µF

25V

×2

+

C3

25

µF

25V

R7

910

Ω

Q1

R6

10k

3.3V

R3

0.25

Ω

R1

78.7k

0.5%

Li-Ion

RECHARGABLE

CELL

GND

R2

34k

0.5%

+

CHARGE

SHUTDOWN

PRECHARGE

CHARGE

•

•

Figure 8. Lithium-Ion Battery Charger