LTC4066/LTC4066-1
17
4066fc
APPLICATIONS INFORMATION
Battery Charger
The battery charger circuits of the LTC4066/LTC4066-1
are designed for charging single cell lithium-ion batter-
ies. Featuring an internal P-channel power MOSFET, the
charger uses a constant-current/constant-voltage charge
algorithm with programmable current and a program-
mable timer for charge termination. Charge current can be
programmed up to 1.5A. The fi nal fl oat voltage accuracy
is ±0.8% typical. No blocking diode or sense resistor is
required when powering the IN pin. The CHRG open-drain
status output provides information regarding the charging
status of the LTC4066/LTC4066-1 at all times. An NTC
input provides the option of charge qualifi cation using
battery temperature.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 105°C. This feature protects
the LTC4066/LTC4066-1 from excessive temperature, and
allows the user to push the limits of the power handling
capability of a given circuit board without risk of dam-
aging the LTC4066/LTC4066-1. Another benefi t of the
LTC4066/LTC4066-1 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 voltage at the OUT pin
rises above the output UVLO level and the battery voltage
is below the recharge threshold. No charge current actually
fl ows until the OUT voltage is greater than the output UVLO
level and 100mV above the BAT voltage. At the beginning
of the charge cycle, if the battery voltage is below 2.8V,
the charger goes into trickle charge mode to bring the
cell voltage up to a safe level for charging. The charger
goes into the fast charge constant-current mode once
the voltage on the BAT pin rises above 2.8V. In constant-
current mode, the charge current is set by R
PROG
. When
the battery approaches the fi nal fl oat voltage, the charge
current begins to decrease as the LTC4066/LTC4066-1
switches to constant-voltage mode. When the charge
current drops below a level programmed by the I
STAT
pin
while in constant-voltage mode the CHRG pin assumes a
high impedance state.
An external capacitor on the TIMER pin sets the total
minimum charge time. When this time elapses the
charge cycle terminates and the CHRG pin assumes a
high impedance state, if it has not already done so. While
charging in constant-current mode, if the charge current
is decreased by thermal regulation or in order to maintain
the programmed input current limit the charge time is
automatically increased. In other words, the charge time
is extended inversely proportional to charge current de-
livered to the battery. For Li-Ion and similar batteries that
require accurate fi nal fl oat potential, the internal bandgap
reference, voltage amplifi er and the resistor divider provide
regulation with ±0.8% accuracy.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage
is low (below 2.8V) 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 charge time, the battery is assumed to be defective,
the charge cycle is terminated and the CHRG pin output
assumes a high impedance state. If for any reason the
battery voltage rises above ~2.8V, the charge cycle will
be restarted. To restart the charge cycle (i.e., when the
dead battery is replaced with a discharged battery), simply
remove the input voltage and reapply it, cycle the TIMER
pin to 0V or cycle the SHDN pin to 0V.
