LTC4065-4.4 Linear Technology, LTC4065-4.4 Datasheet - Page 8

• Manufacturer Part Number: LTC4065-4.4
• Description: Standalone 750mA Li-Ion Battery Charge
• Manufacturer: Linear Technology

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LTC4065-4.4
OPERATIO
The LTC4065-4.4 is a linear battery charger designed
primarily for charging single-cell lithium-ion batteries.
Featuring an internal P-channel power MOSFET, the charger
uses a constant-current/constant-voltage charge algo-
rithm with programmable current. Charge current can be
programmed up to 750mA with a final float voltage accu-
racy of ±0.6%. The CHRG open-drain status output indi-
cates if C/10 has been reached. No blocking diode or
external sense resistor is required; thus, the basic charger
circuit requires only two external components. An internal
termination timer and trickle charge low-battery condi-
tioning adhere to battery manufacturer safety guidelines.
Furthermore, the LTC4065-4.4 is capable of operating
from a USB power source.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 115°C. This feature protects
the LTC4065-4.4 from excessive temperature and allows
the user to push the limits of the power handling capability
of a given circuit board without risk of damaging the
LTC4065-4.4 or external components. Another benefit of
the LTC4065-4.4 thermal limit is that charge current can
be set according to typical, not worst-case, ambient tem-
peratures for a given application with the assurance that
the charger will automatically reduce the current in worst-
case conditions.
The charge cycle begins when the following conditions are
met: the voltage at the V
mately 80mV above the BAT pin voltage, a program
resistor is present from the PROG pin to ground and the EN
pin is pulled below the shutdown threshold (typically
0.82V).
If the BAT pin voltage is below 2.9V, the charger goes into
trickle charge mode, charging the battery at one-tenth the
programmed charge current to bring the cell voltage up to
a safe level for charging. If the BAT pin voltage is above
4.3V, the charger will not charge the battery as the cell is
8
U
CC
pin exceeds 3.6V and approxi-
near full capacity. Otherwise, the charger goes into the fast
charge constant-current mode.
When the BAT pin approaches the final float voltage
(4.4V), the LTC4065-4.4 enters constant-voltage mode
and the charge current begins to decrease. When the
current drops to 10% of the full-scale charge current, an
internal comparator turns off the N-channel MOSFET on
the CHRG pin and the pin assumes a high impedance state.
An internal timer sets the total charge time, t
(typically 4.5 hours). When this time elapses, the charge
cycle terminates and the CHRG pin assumes a high
impedance state. The charge cycle will automatically
restart if the BAT pin voltage falls below V
(typically 4.3V). To restart the charge cycle, remove the
input voltage and reapply it, or momentarily force the EN
pin above V
When the input voltage is not present, the battery drain
current is reduced to less than 4µA. The LTC4065-4.4 can
also be shut down by pulling the EN pin above the shutdown
threshold voltage.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The battery charge current
is 1000 times the current out of the PROG pin. The
program resistor and the charge current are calculated
using the following equations:
The charge current out of the BAT pin can be determined
at any time by monitoring the PROG pin voltage and using
the following equation:
I
R
BAT
PROG
=
R
=
V
PROG
PROG
MS
1000
(typically 0.82V).
• 1000
•
I
CHG
1
V
,
I
CHG
=
1000
R
PROG
V
RECHRG
TIMER
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