LTC4065L/
LTC4065LX/LTC4065L-4.1
10
4065lfb
OPERATION
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in undervoltage lockout until
V
CC
rises above 3.6V
and
approximately 80mV above the
BAT pin voltage. The 3.6V UVLO circuit has a built-in hys-
teresis of approximately 0.6V and the automatic shutdown
threshold has a built-in hysteresis of approximately 50mV.
During undervoltage lockout conditions, maximum battery
drain current is 4μA and maximum supply current is 11μA.
Shutdown Mode
The LTC4065L can be disabled by pulling the EN pin
above the shutdown threshold (approximately 0.82V).
In shutdown mode, the battery drain current is reduced
to less than 1μA and the supply current to about 20μA.
Timer and Recharge
The LTC4065L has an internal termination timer that
starts when an input voltage greater than the undervolt-
age lockout threshold is applied to V
CC
, or when leaving
shutdown the battery voltage is less than the recharge
threshold.
At power-up or when exiting shutdown, if the battery volt-
age is less than the recharge threshold, the charge time is
set to 4.5 hours. If the battery voltage is greater than the
recharge threshold at power-up or when exiting shutdown,
the timer will not start and charging is prevented since the
battery is at or near full capacity.
Once the charge cycle terminates, the LTC4065L continu-
ously monitors the BAT pin voltage using a comparator
with a 2ms filter time. When the average battery voltage
falls 100mV below the float voltage (which corresponds
to 80% to 90% battery capacity), a new charge cycle is
initiated and a 2.25 hour timer begins. This ensures that
the battery is kept at, or near, a fully charged condition and
eliminates the need for periodic charge cycle initiations.
The CHRG output assumes a strong pull-down state during
recharge cycles until C/10 is reached when it transitions
to a high impendance state.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage
is low (below 2.9V), the charger goes into trickle charge,
reducing the charge current to 10% of the full-scale cur-
rent (Note: The LTC4065LX has full charge current at
low-battery voltage). If the low-battery voltage persists
for one quarter of the total time (1.125 hour), the battery
is assumed to be defective, the charge cycle is terminated
and the CHRG pin output pulses at a frequency of 2Hz with
a 75% duty cycle. If for any reason the battery voltage
rises above 2.9V, the charge cycle will be restarted. To
restart the charge cycle (i.e., when the defective battery
is replaced with a discharged battery), simply remove the
input voltage and reapply it or temporarily pull the EN pin
above the shutdown threshold.
CHRG Status Output Pin
The charge status indicator pin has three states: pull-
down, pulse at 2Hz (see Trickle Charge and Defective
Battery Detection) and high impedance. The pull-down
state indicates that the LTC4065L is in a charge cycle. A
high impedance state indicates that the charge current
has dropped below 10% of the full-scale current or the
LTC4065L is disabled. Figure 2 shows the CHRG status
under various conditions.
