LT1571-1 LINER [Linear Technology], LT1571-1 Datasheet - Page 9

• Manufacturer Part Number: LT1571-1
• Description: Constant-Current/ Constant-Voltage Battery Charger with Preset Voltage and Termination Flag
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Lithium-Ion Charging
The circuit in Figure 4 uses the 28-pin LT1571-2 to charge
lithium-ion batteries at a constant 1A until the battery
voltage reaches 8.4V preset battery voltage. The charger
will then automatically go into a constant-voltage mode
with current decreasing to near zero over time as the
battery reaches full charge.
Lithium-Ion Charge Completion
Some battery manufacturers recommend termination of
constant-voltage float mode after charge current has
dropped below a specified level (typically around 10% to
20% of the full current) and a further time-out period of 30
minutes to 90 minutes has elapsed. Check with manufac-
turer for details. The LT1571 provides a signal at the FLAG
pin when the charger is in voltage mode and charge
current has reduced to approximately 20% of full current.
Note that full current is (2.465V 2000)/R
tor E6 in the Block Diagram compares the charge current
sample I
VA. When the charge current drops to 20% of full current,
I
output V
an external timer or to terminate the charge. When this
feature is used, a capacitor of at least 0.1 F is required at
PROG
will be equal to 0.25 I
FLAG
PROG
will go low. This signal can be used to start
to the output current I
U
U
Figure 4. 200kHz Charging Lithium Batteries (Efficiency at 1A > 87%)
VA
NOTE: COMPLETE LITHIUM-ION CHARGER, NO TERMINATION REQUIRED
**
and the open-collector
*
L1**
33 H
W
TOKIN OR MARCON CERAMIC SURFACE MOUNT
COILTRONICS CTX33-2
VA
voltage amplifier
PROG
D2
MMBD914L
0.1 F
C1
0.22 F
MBRM120T3
. Compara-
U
D1
SELECT
BOOST
SENSE
CAP
GND
SW
LT1571-2
PROG
CAP pin to filter out the switching noise and a pull-up
resistor is also needed at FLAG pin.
Charge Termination Flag Threshold Setting
The charge termination flag threshold can be reduced
from the default 20% level to as low as 7.5% of the
programmed full charge current. This is done by adding a
resistor R
The formula for selecting the R
R
BAT2
FLAG
BAT
V
PROG
V
CC
C
R
Threshold
or
CAP
0.3 F
Figure 5. Reducing Charge Termination Threshold
is the charge current setting resistor.
1k
CAP
0 20
+
.
( .
1 F
C
10 F
1 331
from the CAP pin to ground (see Figure 5).
IN
300
C
22 F
TANT
*
0 20
MBRM120T3
–
OUT
.
4.93k
Threshold
)
D3
R
+
– ( .
PROG
0.1 F
1 331
8.4V
LT1571
100k
1571 F04
V
11V
TO 26V
R
CAP
IN
1571 F05
CAP
)
CAP
R
R
PROG
LT1571 Series
CAP
resistor is:
9