Constant-Voltage Battery Charger
n Charger Input Voltage May Be Higher, Equal to or
Lower Than Battery Voltage
n Charges Any Number of Cells Up to 30V*
n 1% Voltage Accuracy for Rechargeable Lithium
n 500kHz Switching Frequency Minimizes
n 100mV Current Sense Voltage for High Efficiency
n Battery Can Be Directly Grounded
n Charging Current Easily Programmable or Shut Down
n Battery Charging of NiCd, NiMH, Lead-Acid or
Lithium Rechargeable Cells
n Precision Current Limited Power Supply
n Constant-Voltage/Constant-Current Supply
n Transducer Excitation
*Maximum Input Voltage = 40V – VBAT
The LT®1512 is a 500kHz current mode switching regulator
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 separated from the
battery itself, simplifying battery switching and system
grounding problems. In addition, these topologies allow
charging even when the input voltage is lower than the
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 current can be
easily programmed for all battery types.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
• L1 A*
S/S FB •
GND GND S VC
*L1 A, L1 B ARE TWO 33µH WINDINGS ON A
SINGLE INDUCTOR: COILTRONICS CTX33-3
**TOKIN CERAMIC 1E225ZY5U-C203-F
Figure 1. SEPIC Charger with 0.5A Output Current
Maximum Charging Current
0.8 CELL (4.1V)
0.4 6V BATTERY
0.2 12V BATTERY
INDUCTOR = 33µH
0 5 10 15 20 25
INPUT VOLTAGE (V)
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.
For more information www.linear.com/LT1512