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LTC4052-4.2 Datasheet(PDF) 6 Page - Linear Technology |
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LTC4052-4.2 Datasheet(HTML) 6 Page - Linear Technology |
6 / 12 page LTC4052-4.2 6 405242f OPERATIO The LTC4052 is a complete lithium-ion battery pulse charger with an internal 0.35 Ω N-MOSFET switch driven by an internal charge pump. The charge current is set by the current limit of the input supply (wall adapter). An external RSENSE sets the maximum allowable charge overcurrent and prevents a wall adapter with a high current limit from damaging the battery. If the current limit of the input supply is above IMAX, the charger will imme- diately turn off the N-MOSFET switch and will retry after 640ms, thus reducing the average charge current to approximately 1% of the overcurrent value (CTIMER = 0.1 µF). If the battery is disconnected while in full charge mode, the charge pump turns off when the voltage at the BAT pin rises above 4.7V and turns back on when the voltage drops below the float voltage. A charge cycle begins when the voltage at the VIN pin rises above the BAT pin by 45mV. The charger will go into trickle charge mode if the battery voltage is below 2.45V. The trickle charge current is preset to 24mA and is provided by an internal current source. In trickle mode, both the pass transistor and charge pump are off. When the cell voltage exceeds 2.45V, the charger goes into full charge mode. In this mode, the charge pump turns on and ramps up the gate voltage of the pass transistor turning it on. The current limited voltage at the VIN pin will ramp down to VBAT plus the voltage drop across the pass transistor and RSENSE, thus reducing the power dissipa- tion in the pass transistor. The charge current is deter- mined by the current limit of the input supply. When the battery voltage reaches the final float voltage, the pass transistor turns off for 100ms (minimum off- time). It remains off as long as the battery voltage stays above the float voltage after the 100ms off-time. After the minimum off-time, if the battery voltage drops below the float voltage, the pass transistor turns back on for at least 400ms (minimum on-time). As the battery approaches full charge, the off-time will get longer and the on-time will stay at 400ms. When the N-MOSFET switch is on, the voltage at the BAT pin will be slightly higher than the final float voltage due to the ESR associated with the battery pack. This voltage level should not be high enough to turn on the overvoltage protection circuitry often located in the battery pack. When the duty cycle at the GATE pin drops below 10%, a comparator turns off the N-FET at the CHRG pin and connects a weak current source (40 µA) to ground to indicate a near end-of-charge C/10 condition. The pulse charging will continue until the timer stops. An external capacitor at the TIMER pin sets the total charge time, the minimum on- and off-time and the overcurrent retry period. After a time-out has occurred, the charge cycle terminates and the CHRG pin is forced high imped- ance. After the charging stops, if the battery voltage drops below 4.05V due to external loading or internal battery leakage current, a new charge cycle will automatically resume. |
Similar Part No. - LTC4052-4.2_15 |
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Similar Description - LTC4052-4.2_15 |
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