Rechargeable lithium-ion battery is the most widely used battery in modern electronic products such as mobile phones and notebook computers, but it is relatively fragile and cannot be overcharged or overdischarged during use (it will damage the battery or make the battery invalid). Therefore, there are protective components or protective circuits for batteries to prevent damage to expensive batteries. Li-ion battery charging requirements are very high. In order to ensure that the terminal voltage accuracy is within ±1%, major semiconductor device manufacturers have developed a variety of lithium-ion battery charging ICs to ensure the safety, reliability, and rapid high-capacity charging of lithium-ion batteries.

　　Mobile phones are mainly powered by lithium-ion batteries. Proper use of lithium-ion batteries is of great significance for extending battery life. According to the requirements of different electronic products, it can be made into plane rectangular, cylindrical, rectangular, button and other shapes, and there are multiple batteries in series and parallel to form a battery pack. Due to changes in materials, the rated voltage of lithium-ion batteries is generally 3.7V, while the positive electrode of lithium iron phosphate (hereinafter referred to as iron phosphate) is 3.2V. When fully charged, the terminal charging voltage is generally 4.2v and 3.65v. The final discharge voltage of lithium-ion batteries is 2.75v~3.0v (the operating voltage range or the final discharge voltage given by the battery manufacturer, each parameter is slightly different, generally 3.0v, phosphorus, iron 2.5v). Discharge below 2.5V (2.0V ferrophosphorus) is called overdischarge and will damage the battery.

　　Li-ion batteries using lithium cobalt oxide cathode materials are not suitable for high-current discharge. Overcurrent discharge will shorten the discharge time (internal temperature rise, energy loss) and may cause danger. The lithium iron phosphate cathode material lithium-ion battery can be charged and discharged with a large current of 20C or greater (C is the battery capacity, such as C=800mAh, 1C charging rate is 800mA), which is particularly suitable for electric vehicles. Therefore, the maximum discharge current supplied by the battery manufacturer should be less than the maximum discharge current in use. Lithium-ion batteries have certain requirements for temperature. The factory provides charging temperature range, discharge temperature range, and storage temperature range. Overvoltage charging can cause permanent damage to the lithium-ion battery. The charging current of lithium-ion batteries should be in accordance with the battery manufacturer’s recommendations, and a limited current circuit should be used to prevent overcurrent (overheating). The commonly used charging rate is 0.25C~1C. During high-current charging, the battery temperature is often tested to prevent overheating from damaging the battery or the appearance of an explosive large-capacity lithium-ion battery.

　　Li-ion battery charging is divided into two stages: the first stage is constant current charging, and when it is close to the termination voltage, it changes to constant voltage charging. For example, the terminal charging voltage of a battery with a capacity of 800mAh is 4.2v. In the constant current charging of the 800 mAh battery (charging rate 1c), the battery voltage starts with a larger ramp up. When the battery voltage is close to 4.2V to 4.2V, the constant voltage charging, the current gradually decreases, and the voltage changes little, so charging The current is 1/10-50c (GeChang has different values and does not affect the use), which is close to full and may terminate the charging (some chargers start the timer 1/10c after pressing the time, and then end the charging).