The working status of lithium-ion battery chargers.3.7 volt 18650 lithium battery

　　(1) Initialize Charge cycle

　　The lithium-ion battery charger will initialize the Charge cycle after it detects the battery and charging power supply. After charging, if it detects that the battery voltage is lower than 3.89V or the voltage of the THERM pin is higher than 1.4V, it will recharge. The condition for allowing fast charging is that the battery voltage is greater than 2.5V and less than the charging threshold voltage (default value is 4.2V), and the temperature range is between 2.5 ° C and 47.5 ° C. If the temperature range does not match, the lithium-ion battery charger will be in a waiting state. When the battery voltage is below 2.5V, the lithium-ion battery charger is pre charged with a current of 5mA to prevent damage or even danger to the deeply discharged lithium-ion battery during fast charging.

　　(2) Fast charging process

　　After the fast charging starts, the lithium-ion battery charger turns on the external P-channel FET, and the charging current is determined by the external current limiting charging power supply. Since the P-channel field-effect transistor works in the switch state, not a linear regulator, so the power consumption is very small. The condition for the end of fast charging is that the battery voltage reaches the threshold (adjusted by the ADJ pin) or the charging time reaches the predetermined fast charging time or the temperature exceeds the safety range. When the temperature exceeds the operating range, the fast charging is only suspended. When the temperature recovers, the fast charging will continue.

　　(3) Pulse charging process

　　In most cases, when the charging battery reaches the threshold value, the fast charging process will end and the pulse charging process will enter. The lithium-ion battery charger will detect the battery voltage every 2ms. When the battery voltage is less than the threshold value, the external P-channel FET will be on. When the battery voltage is greater than or equal to the threshold value, the P-channel FET will be off. When the pulse charging process is near the end, the P-channel FET's off time will greatly exceed the on time, After reaching the cycle ratio set by TSEL pins (1/64,1/128,1/256), the pulse charging process ends.

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