Datasheet

13
LT1513/LT1513-2
sn1513 1513fas
TYPICAL APPLICATIONS
U
Lithium-Ion Battery Charger with
Switchable Charge Current
Many battery chemistries require several constant-current
settings during the charging cycle. The circuit shown in
Figure 8 uses the LT1513-2 to provide switchable 1.35A and
0.13A constant-current modes. The circuit is based on a
standard SEPIC battery charger circuit set to a single
lithium-ion cell charge voltage of 4.1V. The LT1513-2 has I
FB
referenced to ground allowing a simple resistor network to
set the charging current values. In constant-current mode,
the I
FB
error amplifier drives the FB pin, increasing charging
current, until I
R4
is balanced by I
R5
.
I
IRI
R
CHARGE
R FBVOS
=
()()–
5
4
3
There are several ways to control I
R5
including DAC, PWM or
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 V
FB
pin, changing the LT1513-2 to
constant-voltage mode. As charging current falls, the output
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.
LT1513-2
L1A
CTX10-4
L1B
GND
I
FB
1513 F08
V
SW
V
FB
1
7
6
3
5
2
V
C
V
IN
V
IN
S/S
R3
330Ω
R5
36k
R4
4.7k
C5
0.1µF
4
C4
0.22µF
C2
4.7µF
D1
MBRS330T3
C1
22µF
25V
×2
+
C3
25µF
25V
R7
910Ω
Q1
R6
10k
3.3V
R3
0.25Ω
R1
78.7k
0.5%
Li-Ion
RECHARGABLE
CELL
GND
R2
34k
0.5%
+
CHARGE
SHUTDOWN
PRECHARGE
CHARGE
•
•
Figure 8. Lithium-Ion Battery Charger