The principle of lithium battery protection chip, the function of lithium battery protection IC. The working principle of lithium battery protection chip includes overcharge protection, overdischarge protection, overcurrent protection, short circuit protection, etc. In terms of functions, the protection IC does not need to integrate all functions. A single protection IC can be developed according to different lithium battery materials, such as only overcharge protection or overdischarge protection, which can greatly reduce cost and size.
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The principle of lithium battery protection chip
Lithium battery protection board or corresponding BMS, and even various communication protocols will be used in the design of lithium battery PACK, but lithium battery protection is very important. It is necessary to know the working principle of the protection chip. Only understand these basic protection chips. The working principle can better design the lithium battery pack, and even assist the quality part to analyze abnormal batteries or circuits together.
1. Introduction to the main components in the working principle of the protection chip: IC: It is the core of the protection chip. It first samples the battery voltage and then issues various commands through judgment. MOS tube: It mainly acts as a switch.
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 is to use A wire shorts 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 low, MOS2 is turned off, and 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 as 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 issues a command 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 suddenly decreases , IC samples the voltage generated by the sudden increase in current through the VM pin. At this time, the IC samples and issues instructions to turn off MOS1, the loop 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 electrode of the battery through the load, D2, MOS1 to the negative electrode of the battery, and the IC is sampled through the VM pin to a sudden increase The voltage generated by the current is then sampled by the IC and issued a command to turn off MOS1, the circuit is disconnected, and the lithium battery is protected.
Lithium battery protection IC function
In addition to lithium battery protection IC functions such as overcharge protection, overdischarge protection, overcurrent protection and short circuit protection, there are other new protection IC functions for lithium batteries.
1. High precision of overcharge protection
When the lithium ion battery is overcharged, in order to prevent the internal pressure from rising due to temperature rise, the charging state must be cut off. The protection IC will detect the battery voltage, and when overcharge is detected, the power MOSFET of the overcharge detection will cut off and stop charging. At this time, attention should be paid to the high-precision detection voltage of overcharge. 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. Therefore, it is necessary to achieve the allowable voltage When the charging state is cut off. To meet these two conditions at the same time, there must be a high-precision detector. The current precision of the detector 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 fall below the standard value of the specification, at this time it needs to be recharged. If you continue to use it without charging, it may cause the battery to fail to continue to use due to over-discharge. In order to prevent over-discharge, the protection IC must detect the battery voltage. Once it reaches the over-discharge detection voltage or lower, 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 it is necessary to minimize the current consumption of the protection IC.
3. Over current/short circuit protection needs to have low detection voltage and high precision requirements
The discharge must be stopped immediately when a short circuit is caused by an unknown reason. The overcurrent detection 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 detection voltage, the discharge will stop. In order to make the Rds(on) of the power MOSFET effective in charging current and discharging current, it is necessary to make the impedance value as low as possible. At present, the impedance is about 20mΩ~30mΩ, so that the overcurrent detection voltage can be lower.
4. High voltage resistance
When the lithium battery pack is connected to the charger, high voltage will be generated instantly, so the protection IC should meet the requirements of high voltage resistance.
5. Low battery power consumption
In the protection state, its quiescent current consumption must be less than 0.1μA.
6. Zero volt rechargeable
Some lithium batteries may have a voltage as low as 0V due to excessive storage or abnormalities during storage. Therefore, the protection IC needs to be charged at 0V.
The above is the principle of lithium battery protection chip and the function introduction of lithium battery protection IC. The lithium battery protection chip is designed to protect the safety of the battery, that is, to prevent the battery from overcharging and exploding and preventing the battery from being easily damaged by overdischarge. I hope to help you.
