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LTC4065-4.4 Datasheet(PDF) 8 Page - Linear Technology |
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LTC4065-4.4 Datasheet(HTML) 8 Page - Linear Technology |
8 / 16 page 8 LTC4065-4.4 406544f OPERATIO The LTC4065-4.4 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 algo- rithm with programmable current. Charge current can be programmed up to 750mA with a final float voltage accu- racy of ±0.6%. The CHRG open-drain status output indi- cates if C/10 has been reached. No blocking diode or external sense resistor is required; thus, the basic charger circuit requires only two external components. An internal termination timer and trickle charge low-battery condi- tioning adhere to battery manufacturer safety guidelines. Furthermore, the LTC4065-4.4 is capable of operating from a USB power source. An internal thermal limit reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 115 °C. This feature protects the LTC4065-4.4 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 LTC4065-4.4 or external components. Another benefit of the LTC4065-4.4 thermal limit is that charge current can be set according to typical, not worst-case, ambient tem- peratures 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 following conditions are met: the voltage at the VCC pin exceeds 3.6V and approxi- mately 80mV above the BAT pin voltage, a program resistor is present from the PROG pin to ground and the EN pin is pulled below the shutdown threshold (typically 0.82V). If the BAT pin voltage is below 2.9V, the charger goes into trickle charge mode, charging the battery at one-tenth the programmed charge current to bring the cell voltage up to a safe level for charging. If the BAT pin voltage is above 4.3V, the charger will not charge the battery as the cell is near full capacity. Otherwise, the charger goes into the fast charge constant-current mode. When the BAT pin approaches the final float voltage (4.4V), the LTC4065-4.4 enters constant-voltage mode and the charge current begins to decrease. When the current drops to 10% of the full-scale charge current, an internal comparator turns off the N-channel MOSFET on the CHRG pin and the pin assumes a high impedance state. An internal timer sets the total charge time, tTIMER (typically 4.5 hours). When this time elapses, the charge cycle terminates and the CHRG pin assumes a high impedance state. The charge cycle will automatically restart if the BAT pin voltage falls below VRECHRG (typically 4.3V). To restart the charge cycle, remove the input voltage and reapply it, or momentarily force the EN pin above VMS (typically 0.82V). When the input voltage is not present, the battery drain current is reduced to less than 4 µA. The LTC4065-4.4 can also be shut down by pulling the EN pin above the shutdown threshold voltage. Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. The battery charge current is 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: R V I I V R PROG CHG CHG PROG == 1000 1 1000 •, The charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage and using the following equation: I V R BAT PROG PROG = • 1000 |
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