1

LT1512

SEPIC Constant-Current/

Constant-Voltage

Battery Charger

The LT

tor specially configured to create a constant-current/

constant-voltage battery charger. In addition to the usual

voltage feedback node, it has a current sense feedback

circuit for accurately controlling output current of a flyback

or SEPIC (Single-Ended Primary Inductance Converter)

topology charger. These topologies allow the current

sense circuit to be ground referred and completely sepa-

rated from the battery itself, simplifying battery switching

and system grounding problems. In addition, these to-

pologies allow charging even when the input voltage is

lower than the battery voltage.

Maximum switch current on the LT1512 is 1.5A. This

allows battery charging currents up to 1A for a single

lithium-ion cell. Accuracy of 1% in constant-voltage mode

is perfect for lithium battery applications. Charging cur-

rent can be easily programmed for all battery types.

s

Battery Charging of NiCd, NiMH, Lead-Acid

or Lithium Rechargeable Cells

s

Precision Current Limited Power Supply

s

Constant-Voltage/Constant-Current Supply

s

Transducer Excitation

s

Charger Input Voltage May Be Higher, Equal to or

Lower Than Battery Voltage

s

Charges Any Number of Cells Up to 30V*

s

1% Voltage Accuracy for Rechargeable Lithium

Batteries

s

100mV Current Sense Voltage for High Efficiency

s

Battery Can Be Directly Grounded

s

500kHz Switching Frequency Minimizes

Inductor Size

s

Charging Current Easily Programmable or Shut Down

FEATURES

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

Figure 1. SEPIC Charger with 0.5A Output Current

Maximum Charging Current

ACTUAL PROGRAMMED CHARGING CURRENT WILL BE INDEPENDENT OF

INPUT VOLTAGE AND BATTERY VOLTAGE IF IT DOES NOT EXCEED THE

VALUES SHOWN. THESE ARE ELECTRICAL LIMITATIONS BASED ON MAXIMUM

SWITCH CURRENT. PACKAGE THERMAL LIMITATIONS MAY REDUCE

MAXIMUM CHARGING CURRENT. SEE APPLICATIONS INFORMATION.

INPUT VOLTAGE (V)

0

0.6

0.8

1.0

20

1512 TA02

0.4

0.2

0

5

10

15

25

INDUCTOR = 33

µH

DOUBLE

LITHIUM

CELL (8.2V)

6V BATTERY

12V BATTERY

SINGLE

LITHIUM

CELL (4.1V)

LT1512

L1 A*

L1 B*

0.5A

•

GND GND S

FB

1512 F01

SYNC

AND/OR

SHUTDOWN

WALL

ADAPTER

INPUT

S/S

C3

22

µF

25V

C2**

2.2

µF

C5

0.1

µF

*

**

L1 A, L1 B ARE TWO 33

µH WINDINGS ON A

SINGLE INDUCTOR: COILTRONICS CTX33-3

TOKIN CERAMIC 1E225ZY5U-C203-F

C4

0.22

µF

R4

24

Ω

+

CHARGE

SHUTDOWN

•

R1

R2

R3

0.2

Ω

R5

1k

C1

22

µF

25V

+

D1

MBRS130LT3