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LTC4065A Datasheet(PDF) 9 Page - Linear Integrated Systems |
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LTC4065A Datasheet(HTML) 9 Page - Linear Integrated Systems |
9 / 18 page LTC4065L/ LTC4065LX/LTC4065L-4.1 9 4065lfb OPERATION The LTC4065L is a linear battery charger designed primar- ily 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. Charge current can be programmed up to 250mA with a final float voltage accuracy of ±0.6%. The CHRG open-drain status output indicates if C/10 has been reached. No blocking diode or external sense resis- tor is required; thus, the basic charger circuit requires only two external components. An internal termination timer and trickle charge low-battery conditioning adhere to battery manufacturer safety guidelines (Note: The LTC4065LX does not include this trickle charge feature). Furthermore, the LTC4065L 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 LTC4065L 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 LTC4065L or external components. Another benefit of the LTC4065L 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 following conditions are met: the voltage at the VCC pin exceeds 3.6V and ap- proximately 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 (Note: The LTC4065LX does not include this trickle charge feature). If the BAT pin volt- age is above 4.1V for LTC4065L/LTC4065LX or 4.0V for LTC4065L-4.1, 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 (4.2V for LTC4065L/LTC4065LX or 4.1V for LTC4065L-4.1), the LTC4065L 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 compara- tor 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 (typi- cally 4.5 hours). 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 EN pin above VMS (typically 0.82V). The charge cycle will automatically restart if the BAT pin voltage falls below VRECHRG (typically 4.1V). When the input voltage is not present, the battery drain current is reduced to less than 4μA. The LTC4065L can also be shut down by pulling the EN pin above the shutdown threshold voltage. This reduces input quiescent current to less than 20μA and battery drain current to less than 1μA. Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. The battery charge current is 205 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: RPROG = 205 • 1V IBAT ,IBAT = 205V RPROG 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: IBAT = VPROG RPROG •205 |
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