LT1512 Datasheet, PDF (1/12 Pages) Linear Technology – SEPIC Constant-Current/ Constant-Voltage Battery Charger

LT1512
SEPIC Constant-Current/
Constant-Voltage
Battery Charger
FEATURES
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}
U
APPLICATIONS
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}
DESCRIPTION
The LT^®1512 is a 500kHz current mode switching regula-
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.
*Maximum Input Voltage = 40V – V_BAT
, LTC and LT are registered trademarks of Linear Technology Corporation.
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
0.5A
LT1512
S/S
FB
L1 B*
R1
•
GND GND S V_C
I_FB
R4
24Ω
C5
0.1µF
R2
+
C1
22µF
25V
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
1512 F01
Figure 1. SEPIC Charger with 0.5A Output Current
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.
1