Lithium battery protection chip principle and function analysis of protection IC

Principle of Lithium Battery Protection Chip Lithium battery protection board or corresponding BMS or even various communication protocols will be used in the design process of lithium battery PACK, but lithium battery protection is very important. It is necessary to know the working principle of the protection chip, only to know These basic protection chip working principles can better design lithium battery packs, and even assist the quality part to break down abnormal batteries or circuits together. 1. The analysis of the critical components in the working principle of the protection chip: IC: It is the core of the protection chip. First, the battery voltage is sampled, and then various commands are issued through judgment. MOS tube: It is mainly used for switching. 2. The protection chip works normally: the MOS tube on the protection chip may be in the off state at the beginning. After the lithium battery is connected to the protection chip, the MOS tube must be triggered first, and the P+ and P- terminals have output voltage. The common trigger method uses a wire Short-circuit B- and P-. 3. Protection chip overcharge protection: Connect a power supply higher than the battery voltage to P+ and P-, connect the positive pole of the power supply to B+, and connect the negative pole of the power supply to B-. After the power supply is connected, the lithium battery starts to charge and the current flows in the direction The current starts from the positive pole of the power supply and flows through the battery, D1 and MOS2 to the negative pole of the power supply. The IC uses the capacitor to sample the value of the battery voltage. When the battery voltage reaches 4.25v, the IC sends a command to make the pin CO low. The current starts from the positive pole of the power supply, flows through the battery, D1, and reaches MOS2 because the gate of MOS2 is connected to CO and is also at low level, MOS2 is turned off, the entire loop is turned off, and the circuit plays a protective role. 4. Protection chip over-discharge protection: After connecting a suitable load to P+ and P-, the battery starts to discharge its current direction is like I2, and the current flows from the positive pole of the battery through the load, D2 and MOS1 to the negative pole of the battery; when the battery is discharged When it reaches 2.5v, the IC samples and sends out instructions to turn off MOS1, the circuit is disconnected, and the battery is protected. 5. Overcurrent protection: After connecting a suitable load to P+ and P-, the battery starts to discharge and its current direction is like I2. The current flows from the positive pole of the battery through the load, D2 and MOS1 to the negative pole of the battery. When the load decreases suddenly , IC sampled through VM pin to the voltage appearing by sudden increase of current. At this time, IC samples and issues instructions to cut off MOS1, the circuit is disconnected, and the battery is protected. 6. Short circuit protection: After connecting an empty load to P+ and P-, the battery starts to discharge the current direction as I2. The current flows from the positive pole of the battery through the load, D2, MOS1 to the negative pole of the battery, and the IC is sampled through the VM pin to a sudden increase At this time, the voltage generated by the current is sampled by the IC and commands are issued to cut off MOS1, the circuit is disconnected, and the lithium battery is protected. Functions of Lithium Battery Protection IC In addition to lithium battery protection IC functions such as overcharge protection, overdischarge protection, overcurrent protection, and short circuit protection, lithium batteries also have other new protection IC functions. 1. High-precision overcharge protection. When the lithium battery is overcharged, the charge state must be cut off in order to guard against the increase in internal pressure caused by the temperature rise. The protection IC will test the battery voltage, and when the test is overcharged, the power MOSFET of the overcharge test will be cut off to cut off the charge. At this time, attention should be paid to the high precision of the test voltage for overcharging. When the battery is charged, the user is very concerned about charging the battery to a full state. At the same time, safety issues must be taken into account, so the allowable voltage must be reached. When the charging state is cut off. To meet these two conditions at the same time, it is necessary to have a high-precision tester. The current precision of the tester is 25mV, and this precision needs to be further improved. 2. Reduce the power consumption of the protection IC. As the use time increases, the voltage of the charged lithium battery will gradually decrease, and finally it will fall below the standard value of the specification. At this time, it will be recharged. If the battery is not charged and used continuously, it may cause the battery to be unable to be used continuously due to over-discharge. In order to guard against over-discharge, the protection IC must test the battery voltage. Once it reaches the over-discharge test voltage, the power MOSFET on the discharge side must be cut off to cut off the discharge. But at this time, the battery itself still has natural discharge and current consumption of the protection IC, so the current consumption of the protection IC must be minimized. 3. Over-current/short-circuit protection requires low test voltage and high-precision requirements. Discharge must be stopped immediately when a short circuit is caused for unknown reasons. The overcurrent test uses the Rds(on) of the power MOSFET as the inductive impedance to monitor the voltage drop. If the voltage at this time is higher than the overcurrent test voltage, the discharge will stop. In order to make the Rds(on) of the power MOSFET effectively used in charging current and discharging current, the impedance value needs to be as low as possible. At present, the impedance is about 20m~30m, so the overcurrent test voltage can be lower. 4. When the high-voltage-resistant lithium battery pack is connected to the charger, high voltage will appear instantly, so the protection IC should meet the requirements of high-voltage resistance. 5. Low battery power consumption When in the protection state, its static current consumption must be as small as 0.1μA. 6. Zero-volt rechargeable some lithium batteries may cause the voltage to be too low during storage due to too long or abnormal reasons. 0V, so the protection IC can also be charged at 0V. Indication: The articles published on this website are all from the Internet. If there is any infringement, please contact to delete it. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: What are the commonly used tapes for lithium battery assembly?