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LTC4064 Datasheet(PDF) 8 Page - Linear Technology |
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LTC4064 Datasheet(HTML) 8 Page - Linear Technology |
8 / 16 page LTC4064 8 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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