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LTC4064

4064f

The LTC4064 is a linear battery charger designed primarily

for charging single cell lithium-ion batteries used in back-

up applications. With a 4V final float voltage accuracy of

±1%, the LTC4064 maximizes the lifetime of 4.2V chem-

istry lithium-ion batteries. A precision, automatic recharge

feature ensures that the battery voltage remains within

100mV of this 4V float voltage at all times.

Featuring an internal P-channel power MOSFET, the charger

uses a constant-current/constant-voltage charge algo-

rithm with programmable current and a programmable

timer for charge termination. Charge current can be

programmed up to 1.25A with an accuracy of

±7%. 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 LTC4064 at all times.

An NTC thermistor input

provides 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 LTC4064 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 LTC4064

or the external components. Another benefit of the LTC4064

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 VCC 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 RPROG.

When the battery approaches the final float voltage, the

charge current begins to decrease as the LTC4064 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 (30

µA) 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 VCC.

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.

When the input voltage is not present, the charger goes

into a sleep mode, dropping battery drain current, IBAT, to

less than 3

µA.Thisgreatlyreducesthecurrentdrainonthe

battery and increases the standby time. The charger can be

shut down (ICC = 25µA) by forcing the SHDN pin to 0V.

OPERATIO

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