LT1512_15 Datasheet, PDF (1/14 Pages) Linear Technology – SEPIC Constant-Current/ Constant-Voltage Battery Charger

LT1512
SEPIC Constant-Current/
Constant-Voltage Battery Charger
Features
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}
Batteries
n _{500kHz Switching Frequency Minimizes}
Inductor Size
n _{100mV Current Sense Voltage for High Efficiency}
n _{Battery Can Be Directly Grounded}
n _{Charging Current Easily Programmable or Shut Down}
Applications
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 – V_BAT
Description
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
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 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.
Typical Application
WALL
ADAPTER
INPUT
+
C3
22µF
CHARGE
25V
SYNC
AND/OR
SHUTDOWN
SHUTDOWN
• ^{L1 A*}
V_IN
V_SW
C2**
D1
2.2µF _MBRS130LT3
LT1512
S/S
FB
L1 B*
R1
•
GND GND S V_C
I_FB
R4
R2
24Ω
C5
0.1µF
R5
1k
C4
0.22µF
R3
0.2Ω
*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
0.5A
+ C1
22µF
25V
1512 F01
Maximum Charging Current
1.0
SINGLE
LITHIUM
0.8 CELL (4.1V)
0.6
DOUBLE
LITHIUM
CELL (8.2V)
0.4
6V BATTERY
12V BATTERY
0.2
INDUCTOR = 33µH
0
0
5
10
15
20
25
INPUT VOLTAGE (V)
1512 TA02
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.
1512fc
For more information www.linear.com/LT1512
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