LTC1731-4.1 Linear Technology, LTC1731-4.1 Datasheet - Page 4

• Manufacturer Part Number: LTC1731-4.1
• Description: Lithium-Ion Linear Battery Charger Controller
• Manufacturer: Linear Technology

OPERATIO
LTC1731-4.1
BLOCK DIAGRA
The LTC1731 is a linear battery charger controller. The
charge current is programmed by the combination of a
program resistor (R
and a sense resistor (R
pins. R
trimmed 800 resistor setting up a voltage drop from V
to the input of the current amplifier (CA). The current
amplifier servos the gate of the external P-channel MOSFET
to force the same voltage drop across R
the charge current. When the potential at the BAT pin
approaches the preset float voltage, the voltage amplifier
(VA) will start sinking current which reduces the voltage
drop across R
4
PROG
2
3
BATTERY CURRENT I
sets a program current through an internal
SENSE
TIMER
CHRG
U
, thus reducing the charge current.
PROG
SENSE
) from the PROG pin to ground
100 A
BAT
W
) between the V
= (2.457V • 800 )/(R
SHDN
C/10
C3
OSCILLATOR
LOGIC
STOP
+
–
V
SENSE
REF
C/10
SLP
PROG
CC
+
–
and SENSE
• R
which sets
A1
COUNTER
SENSE
)
C1
CC
+
–
V
CC
7
5
80
720
R
PROG
Charging begins when the potential at V
the UVLO level and a program resistor is connected from
the PROG pin to ground. At the beginning of the charge
cycle, if the cell voltage is below 2.457V, the charger goes
into trickle charge mode. The trickle charge current is 10%
of the full-scale current. If the cell voltage stays low for one
quarter of the total charge time, the charge sequence will
be terminated immediately.
The charger goes into the fast charge constant-current
mode after the voltage on the BAT pin rises above 2.457V.
In constant-current mode, the charge current is set by the
combination of R
PROG
V
CC
2.5 A
LBO
800
–
+
CA
SENSE
CHARGE
C2
VA
C4
and R
+
–
–
+
–
+
2.457V
V
REF
GND
+
–
PROG
54mV
SENSE
4
DRV
BAT
.
1731 BD
8
6
1
CC
pin rises above
R
SENSE