LT1513/LT1513-2
U
TYPICAL APPLICATIONS
Lithium-Ion Battery Charger with
Switchable Charge Current
(I )(R4) – I
R5
FBVOS
I
=
CHARGE
R3
Many battery chemistries require several constant-current
settings during the charging cycle. The circuit shown in
Figure8usestheLT1513-2toprovideswitchable1.35Aand
0.13A constant-current modes. The circuit is based on a
standard SEPIC battery charger circuit set to a single
lithium-ioncellchargevoltageof4.1V.TheLT1513-2hasIFB
referenced to ground allowing a simple resistor network to
set the charging current values. In constant-current mode,
the IFB error amplifier drives the FB pin, increasing charging
current, until IR4 is balanced by IR5.
ThereareseveralwaystocontrolIR5includingDAC,PWMor
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,
R2) starts driving the VFB pin, changing the LT1513-2 to
constant-voltagemode.Aschargingcurrentfalls,theoutput
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.
C2
4.7µF
D1
L1A
CTX10-4
MBRS330T3
Li-Ion
V
RECHARGABLE
CELL
IN
•
+
C3
7
R1
78.7k
0.5%
5
2
3
25µF
V
V
L1B
IN
SW
25V
CHARGE
6
1
•
S/S
V
FB
LT1513-2
SHUTDOWN
C1
+
3.3V
V
I
FB
C
22µF
25V
×2
R3
330Ω
R6
10k
GND
4
R4
4.7k
R5
36k
R7
R2
34k
0.5%
910Ω
R3
0.25Ω
C5
0.1µF
C4
0.22µF
PRECHARGE
CHARGE
Q1
GND
1513 F08
Figure 8. Lithium-Ion Battery Charger
13
Linear [ Linear ]
