LTC4065-4.4 Linear Technology, LTC4065-4.4 Datasheet - Page 9

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

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OPERATIO
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in undervoltage lockout
until V
the BAT pin voltage. The 3.6V UVLO circuit has a built-in
hysteresis of approximately 0.6V and the automatic shut-
down threshold has a built-in hysteresis of approximately
50mV. During undervoltage lockout conditions, maxi-
mum battery drain current is 4µA and maximum supply
current is 11µA.
Shutdown Mode
The LTC4065-4.4 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 LTC4065-4.4 has an internal termination timer that
starts when an input voltage greater than the undervoltage
lockout threshold is applied to V
shutdown the battery voltage is less than the recharge
threshold.
At power-up or when exiting shutdown, if the battery
voltage 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 shut-
down, the timer will not start and charging is prevented
since the battery is at or near full capacity.
CC
rises above 3.6V and approximately 80mV above
U
CC
, or when leaving
Once the charge cycle terminates, the LTC4065-4.4 con-
tinuously monitors the BAT pin voltage using a compara-
tor with a 2ms filter time. When the average battery voltage
falls below 4.3V (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
current. 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 dis-
charged battery less than 2.9V), simply remove the input
voltage and reapply it, or temporarily pull the EN pin above
the shutdown threshold.
LTC4065-4.4
406544f
9