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LTC4002-4.2 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4002-4.2 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page LTC4002-4.2 9 400242i OPERATIO The LTC4002 is a constant current, constant voltage Li-Ion battery charger controller that uses a current mode PWM step-down (buck) switching architecture. The charge current is set by an external sense resistor (RSENSE) across the SENSE and BAT pins. The final battery float voltage is internally set to 4.2V. For batteries like lithium- ion that require accurate final float voltage, the internal 2.465V reference, voltage amplifier and the resistor di- vider provide regulation with ±1% accuracy. A charge cycle begins when the voltage at the VCC pin rises above the UVLO level (4.2V) and is 250mV or more greater than the battery voltage. At the beginning of the charge cycle, if the battery voltage is less than 2.9V, the charger goes into trickle charge mode. The trickle charge current is internally set to 10% of the full-scale current. If the battery voltage stays low for 30 minutes, the battery is considered faulty and the charge cycle is terminated. When the battery voltage exceeds 2.9V, the charger goes into the full-scale constant current charge mode. In con- stant current mode, the charge current is set by the external sense resistor RSENSE and an internal 100mV reference; IBAT = 100mV/RSENSE. When the battery voltage approaches the programmed float voltage, the charge current will start to decrease. When the current drops to 25% of the full-scale charge current, an internal comparator turns off the internal pull- down N-channel MOSFET at the CHRG pin, and connects a weak current source to ground to indicate a near end-of- charge condition. An internal 3 hour timer determines the total charge time. After a time out occurs, the charge cycle is terminated and the CHRG pin is forced high impedance. To restart the charge cycle, remove and reapply the input voltage or momentarily shut the charger down. Also, a new charge cycle will begin if the battery voltage drops below the recharge threshold voltage of 4.05V. When the input voltage is present, the charger can be shut down (ICC = 3mA) by pulling the COMP pin low. When the input voltage is not present, the charger goes into sleep mode, dropping ICC to 10µA. This will greatly reduce the current drain on the battery and increase the standby time. A 10k ΩNTC(negativetemperaturecoefficient)thermistor can be connected from the NTC pin to ground for battery temperature qualification. The charge cycle is suspended when the temperature is outside of the 0 °C to 50°C window (with DALE NTHS-1206N02). |
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