LTC4053-4.2_15 Datasheet, PDF (10/16 Pages) Linear Technology – USB Compatible Lithium-Ion Battery Charger with Thermal Regulation

LTC4053-4.2
APPLICATIO S I FOR ATIO
Programming The Timer
The programmable timer is used to terminate the charge
cycle. The timer duration is programmed by an external
capacitor at the TIMER pin. The total charge time is:
Time (Hours) = (3 Hours) • (C_TIMER/0.1µF) or
C_TIMER = 0.1µF • Time (Hours)/3 (Hours)
The timer starts when an input voltage greater than the
undervoltage lockout threshold level is applied and the
SHDN pin is greater than the manual shutdown threshold
voltage level. After a time-out occurs, the charge current
stops, and the CHRG output assumes a high impedance
state to indicate that the charging has stopped. Connect-
ing the TIMER pin to ground disables the timer function.
Recharge
After a charge cycle has terminated, if the battery voltage
drops below the recharge threshold of 4.05V a new charge
cycle will begin. The recharge circuit integrates the BAT
pin voltage for a few milliseconds to prevent a transient
from restarting the charge cycle.
If the battery voltage remains below 2.48V during trickle
charge for 1/4 of the programmed time, the battery may be
defective and the charge cycle will end. In addition, the
recharge comparator is disabled and a new charge cycle
will not begin unless the input voltage is toggled off-then-
on, the SHDN pin is momentarily pulled to ground, or the
BAT pin is pulled above the 2.48V trickle charge threshold.
Open-Drain Status Outputs
The LTC4053 has three open-drain status outputs: ACPR,
CHRG and FAULT. The ACPR pin pulls low when an input
voltage greater than the undervoltage lockout threshold is
applied and becomes high impedance when power (V_IN <
V_UV) is removed. CHRG and FAULT work together to
indicate the status of the charge cycle. Table 1 describes
the status of the charge cycle based on the CHRG and
FAULT outputs.
Table 1.
FAULT
High
Low
High
CHRG
Low
Low
30µA
pull-down
Description
Charge cycle has started, C/10 has not been
reached and charging is proceeding normally.
Charge cycle has started, C/10 has not been
reached, but the charge current and timer
have been paused due to an NTC out-of-
temperature condition.
C/10 has been reached and charging is
proceeding normally.
Low
30µA C/10 has been reached but the charge current
pull-down and timer have paused due to an NTC out-of-
temperature condition.
High
High Normal timeout (charging has terminated).
Low
High If FAULT goes low and CHRG goes high
impedance simultaneously, then the LTC4053
has timed out due to a bad cell (V_BAT <2.48V
after one-quarter the programmed charge time).
If CHRG goes high impedance first, then
the LTC4053 has timed out normally (charging
has terminated), but NTC is indicating an out-
of-temperature condition.
CHRG Status Output Pin
When the charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET capable of
driving an LED. When the charge current drops to 10% of
the full-scale current (C/10), the N-channel MOSFET is
latched off and a weak 30µA current source to ground is
connected to the CHRG pin. After a time-out occurs,
the pin assumes a high impedance state. By using two
different value pull-up resistors a microprocessor can
detect three states from this pin (charging, C/10 and time-
out). See Figure 3.
When the LTC4053 is in charge mode, the CHRG pin is
pulled low by the internal N-channel MOSFET. To detect
this mode, force the digital output pin, OUT, high and
measure the voltage at the CHRG pin. The N-channel
MOSFET will pull the pin low even with the 2k pull-up
resistor. Once the charge current drops to 10% of the
4053fa
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