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- Time：2023/10/31 Posted：Shenzhen Xinfeihong Electronics Co., Ltd
- Currently, lithium batteries are widely used in various electronic products such as mobile phones, computers, and tablets. That is to say, we come into contact with lithium batteries every day, but if lithium batteries are not properly protected, there may also be hidden dangers. So, when designing lithium batteries, it is necessary to use lithium battery protection plates or corresponding BMS, because the protection of lithium batteries is very important. Today, a question introduced by the editor of Shenzhen Tedeland Electronic Network is what is the principle of lithium battery protection chips< Br/>
Lithium battery protection chip
1、 Introduction to the main components in the working principle of protective chips:
IC: Sampling the battery voltage and issuing various commands for protection based on judgment is the core of the protection chip
MOS transistor: mainly used for switch control< Br/>
Protection chip works normally:
The initial state of the MOS transistor on the protection chip may be off. After the lithium battery is connected to the protection chip, the MOS transistor is first triggered, and only the P+and P-terminals have output voltage, triggering the commonly used method of short circuiting the B-terminal with a wire< Br/>
Protection chip overcharge protection:
Connect a power supply with a voltage higher than the battery voltage between P+and P -, with the positive pole of the power supply connected to B+and the negative pole of the power supply connected to B. After connecting to the power supply, the lithium battery begins to charge, and the current direction flows towards the current, from the positive pole of the power supply to the negative pole of the power supply through the battery, D1, MOS2. The IC samples the battery voltage value through a capacitor. When the battery voltage reaches 4.25v, the IC issues a command to place pin CO at a low level. At this point, the current starts from the positive pole of the power supply and flows through the battery, providing protection for the circuit< Br/>
Protection chip over discharge protection:
After P+is connected to P - with appropriate load, the battery begins to discharge, such as 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 battery is discharged to 2.5 V, the IC samples and issues a command to turn off MOS1, disconnect the circuit, and protect the battery< Br/>
Overcurrent protection:
When P+is connected to the appropriate load of P -, the battery begins to discharge, with a current direction such as 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, the IC samples the voltage generated by the sudden increase in current through the VM pin, and the IC samples and issues instructions to cut off MOS1 and disconnect the battery from the circuit< Br/>
Short circuit protection:
After P+is connected to the load on P -, the battery begins to discharge the current direction, such as I2. The current flows from the positive pole of the battery through the load, D2, and MOS1 to the negative pole of the battery. The IC collects the voltage generated by the sudden increase in current through the VM pin, and then samples and sends instructions to let MOS1 cut off, and the circuit disconnects the lithium battery< Br/>
2、 Function of lithium battery protection IC
In addition to the protective IC functions of lithium-ion batteries such as overcharging protection, over discharge protection, overcurrent protection, and short circuit protection, there are also other new protective IC functions for lithium-ion batteries< Br/>
1. High precision of overcharging protection
When a lithium-ion battery is in an overcharged state, in order to prevent the internal pressure from increasing due to temperature rise, the charging state must be stopped. The protection IC will detect battery voltage. When overcharging is detected, the power MOSFET for overcharging detection will cut off and stop charging. At this point, attention should be paid to high-precision overcharging detection voltage. When charging the battery, users are very concerned about charging the battery to its full state and considering safety issues. Therefore, when the allowable voltage is reached, it is necessary to stop the charging state. In order to meet both conditions simultaneously, high-precision detectors are necessary. At present, the accuracy of the detector is 25mV, which needs further improvement< Br/>
2. Reduce power consumption of protection IC
As the usage time increases, the voltage of the rechargeable lithium battery will gradually decrease, ultimately falling below the specifications and standard values. At this point, it is necessary to charge again. If used without charging, the battery may become unusable due to excessive discharge. To prevent excessive discharge, it is necessary to detect the battery voltage to protect the IC. Once the excessive discharge detection voltage is reached below, the power MOSFET of the discharge side must be cut off and the discharge must be cut off. However, at this point, the battery itself still has natural discharge and IC protection current consumption, so it is necessary to minimize the current consumption of IC protection< Br/>
3. Overcurrent/short circuit protection requires low detection voltage and high precision
When a short circuit is caused by unknown reasons, the discharge must be immediately stopped. Overcurrent detection uses the Rds (on) of power MOSFETs as the induced impedance to monitor the voltage drop. At this point, if the voltage is higher than the overcurrent detection voltage, the discharge will stop. In order to effectively apply the Rds (on) of power MOSFETs in charging and discharging currents, the impedance value should be as low as possible. At present, the impedance is about 20m Ω -30m Ω, and the overcurrent detection voltage is relatively low< Br/>
4. High voltage resistance
Due to the instantaneous generation of high voltage during the charging process of lithium battery packs, the protection IC should meet the high voltage resistance requirements< Br/>
5. Low battery power consumption
In the protection state, its static current consumption must be 0.1 less than μ A.
6. Zero voltage rechargeable
Some lithium batteries may experience voltage drops to 0 V during storage due to prolonged storage time or abnormal conditions. Therefore, it is necessary to protect the IC from charging at 0 V< Br/>
Alright, if you need to purchase lithium battery protection chips, you can consult Shenzhen Tedeland Electronics. We are a long-term agent for domestic and foreign battery protection chips< Br/>
