LTC4053-4.2
8
4053fa
The LTC4053 is a linear battery charger designed primarily
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 and a programmable timer for
charge termination. Charge current can be programmed
up to 1.25A with a final float voltage accuracy of ±1%. No
blocking diode or sense resistor is required thus dropping
the external component count to three for the basic
charger circuit. The CHRG, ACPR, and FAULT open-drain
status outputs provide information regarding the status of
the LTC4053 at all times. An NTC thermistor input pro-
vides the option of charge qualification 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 LTC4053 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 LTC4053
or the external components. Another benefit of the LTC4053
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 auto-
matically reduce the current in worst-case conditions.
The charge cycle begins when the voltage at the V
CC
pin
rises above the UVLO level, a program resistor is con-
nected from the PROG pin to ground, and the SHDN pin is
pulled above the shutdown threshold. At the beginning of
the charge cycle, if the battery voltage is below 2.48V, 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 2.48V. In constant-
current mode, the charge current is set by R
PROG
.
When the battery approaches the final float voltage, the
charge current begins to decrease as the LTC4053 enters
the constant-voltage mode. When the current drops to
10% of the full-scale charge current, an internal compara-
tor latches off the MOSFET on the CHRG pin and connects
a weak current source to ground (30µA) to indicate a near
end-of-charge (C/10) condition. The C/10 latch can be
cleared by grounding the SHDN pin momentarily, or
momentarily removing and reapplying V
CC
.
An external capacitor on the TIMER pin sets the total
charge time. 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 SHDN pin to 0V.
The charge cycle will also restart if the BAT pin voltage falls
below the recharge threshold.
For lithium-ion and similar batteries that require an accu-
rate final float voltage, the internal reference, voltage
amplifier and the resistor divider provide regulation with
±1% (max) accuracy.
When the input voltage is not present, the charger goes
into a sleep mode, dropping battery drain current, I
BAT
, to
less than 5µA. This greatly reduces the current drain on the
battery and increases the standby time. The charger can be
shut down (I
CC
= 25µA) by forcing the SHDN pin to 0V.
OPERATIO
U
