The principle and function of lithium-ion battery protection chips. The need for protection in lithium-ion batteries stems from their inherent characteristics. Due to the materials used in lithium-ion batteries, they cannot withstand overcharging, over-discharging, overcurrent, short circuits, or excessively high temperatures during charging and discharging. Therefore, lithium-ion battery modules are always accompanied by a sophisticated protection board and a current fuse. Below, a lithium-ion battery manufacturer explains the principle and function of lithium-ion battery protection chips.
The protection function of lithium-ion batteries is usually accomplished by the protection circuit board and current devices such as PTC. The protection circuit board is composed of electronic circuits that accurately monitors the voltage of the cell and the current of the charging and discharging circuit at all times in an environment ranging from -40℃ to +85℃, and controls the opening and closing of the current circuit in a timely manner. The PTC prevents the battery from being severely damaged in high-temperature environments.
Principle of lithium-ion battery protection chips
1. Introduction to key components in the working principle of a protection chip: IC: It is the core of the protection chip. First, it samples the battery voltage, and then issues various commands based on the judgment. MOSFET: It mainly functions as a switch.
2. Normal operation of the protection chip: The MOSFET on the protection chip may be in the off state at the beginning. After the battery is connected to the protection chip, the MOSFET must be triggered first so that there will be an output voltage at the P+ and P- terminals. The common triggering method is to short-circuit B- and P- with a wire.
3. Over-discharge protection chip: After a suitable load is connected to P+ and P-, the lithium-ion battery pack begins to discharge. The current flows from the positive terminal of the battery through the load, D2, MOS1 to the negative terminal of the battery. When the battery discharges to 2.5V, the IC samples and sends a command to turn off MOS1, disconnecting the circuit and protecting the battery.
5. Overcurrent protection: After a suitable load is connected to P+ and P-, the battery begins to discharge. The current direction is as shown by I2. The current flows from the positive terminal of the battery through the load, D2, MOS1 to the negative terminal of the battery. When the load suddenly decreases, the IC samples the voltage that appears due to the sudden increase in current through the VM pin. At this time, the IC samples and issues a command to turn off MOS1, disconnect the circuit, and protect the battery.
6. Short circuit protection: After an unloaded load is connected to P+ and P-, the battery starts to discharge. The current direction is as shown by I2. The current flows from the positive terminal of the battery through the load, D2, MOS1 to the negative terminal of the battery. The IC samples the voltage that appears due to the sudden increase in current through the VM pin. At this time, the IC samples and sends a command to turn off MOS1, disconnect the circuit, and protect the lithium-ion battery.
Functions of lithium battery protection chips
Normal state: When all lithium battery voltages are between the overcharge detection voltage and the over-discharge detection voltage, and the voltages are between the overcurrent detection voltage and the abnormal charging detection voltage, the battery is in normal working condition.
Overcharge state: Under normal conditions, if any external battery voltage is higher than the overcharge detection voltage and exceeds the overcharge protection delay time, the output high impedance state will shut off charging and enter the overcharge protection state; within the overcharge protection delay time, if the detected battery voltage is lower than the overcharge detection voltage for a period of time exceeding the overcharge reset delay time, the accumulated overcharge delay time will be reset; otherwise, the drop in battery voltage will be considered an irrelevant interference and thus shielded.
Over-discharge state: Under normal conditions, if the voltage of any external battery is lower than the over-discharge protection voltage and exceeds the over-discharge protection delay time, the output will be low to shut off the discharge and enter the over-discharge protection state. At the same time, the output will be high impedance to shut off charging.
Lithium-ion batteries are widely used due to their large discharge current, low internal resistance, long lifespan, and lack of memory effect. However, overcharging, over-discharging, and short-circuiting are strictly prohibited, as these can lead to fatal defects such as fires and explosions. Therefore, rechargeable lithium-ion batteries are typically equipped with a protection board to safeguard the cells. This protection board primarily consists of overvoltage and overcurrent protection and is designed to protect the lithium-ion battery cells.
Besides the control IC, another important component in the circuit is the MOSFET, which acts as a switch. Because it is directly connected in series between the battery and the external load, its on-resistance affects the battery's performance.
