LTC4065L/
LTC4065LX/LTC4065L-4.1
OPERATION
The LTC4065L is a linear battery charger designed primar-
ily for charging single cell lithium-ion batteries. Featuring
an internal P-channel power MOSFET, the charger uses a
constant-current/constant-voltage charge algorithm with
programmable current. Charge current can be programmed
up to 250mA with a final float voltage accuracy of ±0.6%.
The
CHRG
open-drain status output indicates if C/10 has
been reached. No blocking diode or external sense resis-
tor is required; thus, the basic charger circuit requires
only two external components. An internal termination
timer and trickle charge low-battery conditioning adhere
to battery manufacturer safety guidelines (Note: The
LTC4065LX does not include this trickle charge feature).
Furthermore, the LTC4065L 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 LTC4065L 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 LTC4065L
or external components. Another benefit of the LTC4065L
thermal limit is that charge current can be set according
to typical, not worst-case, ambient temperatures 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
CC
pin exceeds 3.6V and ap-
proximately 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 (Note: The LTC4065LX does
not include this trickle charge feature). If the BAT pin volt-
age is above 4.1V for LTC4065L/LTC4065LX or 4.0V for
LTC4065L-4.1, the charger will not charge the battery as
the cell is near full capacity. Otherwise, the charger goes
into the fast charge constant-current mode.
When the BAT pin approaches the final float voltage (4.2V
for LTC4065L/LTC4065LX or 4.1V for LTC4065L-4.1), the
LTC4065L 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 compara-
tor 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
TIMER
(typi-
cally 4.5 hours). When this time elapses, the charge cycle
terminates and the
CHRG
pin assumes a high impedance
state. To restart the charge cycle, remove the input voltage
and reapply it or momentarily force the
EN
pin above V
MS
(typically 0.82V). The charge cycle will automatically restart
if the BAT pin voltage falls below V
RECHRG
(typically 4.1V).
When the input voltage is not present, the battery drain
current is reduced to less than 4μA. The LTC4065L can also
be shut down by pulling the
EN
pin above the shutdown
threshold voltage. This reduces input quiescent current to
less than 20μA and battery drain current to less than 1μA.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The battery charge current
is 205 times the current out of the PROG pin. The program
resistor and the charge current are calculated using the
following equations:
R
PROG
=
205 •
1V
I
BAT
, I
BAT
=
205V
R
PROG
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
BAT
=
V
PROG
•205
R
PROG
4065lfb
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LINEAR [ LINEAR INTEGRATED SYSTEMS ]
