The PTC polymer protection component is the simplest protector that protects the lithium-ion battery from damage caused by excessive charging, discharging current or short circuit during charging or discharging. However, it can not solve the problem that the charging voltage is too high during the charging process (overcharge) or the battery voltage during the discharging process is too low (below the termination discharge voltage, called overdischarge), so a fully functional protector integrated circuit has been developed.
The basic parameters of a lithium-ion battery The rated voltage of a lithium-ion battery is 3.6V (a few is 3.7V). The termination charge voltage at full charge is related to the battery anode material: 4.2V for graphite; 4.1V for coke. The accuracy required to terminate the charging voltage during charging is within ±1%. The termination discharge voltage of a lithium ion battery is 2.4 to 2.7 V (the parameters given by the battery manufacturer for the operating voltage range or the termination discharge voltage are slightly different). The battery is damaged above the termination charging voltage and below the termination discharge.
There are certain requirements for use: charging temperature 0 ~ 45 ° C; discharge or storage temperature -20 ~ +60 ° C. Lithium-ion batteries are not suitable for charging and discharging large currents. Generally, the charging current is not more than 1C, and the discharging current is not more than 2C (C is the capacity of the battery, such as C=950mAh, and the charging rate of 1C is 950mA).
Charging and discharging are better at around 20 °C, can not be charged at negative temperature, and the discharge effect is poor. (The discharge effect is the worst at -20 °C, not only the discharge voltage is low, but the discharge time is less than half of that at 20 °C discharge) .
Lithium-ion battery protector IC
Lithium-ion battery protector ICs are available in single-cell and 2- to 4-cell battery packs. The requirements for this type of protector are described here, with a focus on the single-cell Li-Ion battery protector circuit.
Basic requirements for lithium ion battery protectors:
1. When charging, it should be full, and the accuracy of terminating the charging voltage should be protected by ±1%;
2. In the process of charging and discharging, it does not flow, and there is short circuit protection;
3. It is forbidden to continue discharging until the termination discharge voltage is reached, and the accuracy of the termination discharge voltage is about ±3%;
4. A deeply discharged battery (below the termination discharge voltage) is pre-charged in a turbulent manner prior to charging;
5. In order to ensure stable and reliable operation and prevent interference from transient voltage changes, there are internal delay circuits for overcharge, overdischarge and overcurrent protection to prevent malfunction caused by transient interference;
6. When charging a plurality of battery packs connected in series, it is necessary to protect the matching balance of the battery voltages of each section, and the matching accuracy is required to be about ±10%;
7. The power consumption is saved (the protector is energized when charging or discharging). The power consumption of a single-cell battery protector is generally less than 10μA, and the multi-section is generally around 20μA; when it reaches the termination discharge, it is in a closed state, generally consumes less than 2μA;
8. The protector circuit is simple, has few peripheral components, and takes up a small space, and can be used in a battery or a battery pack;
9. The price is low.
Single-cell Li-Ion Battery Protector The AIC1811 single-cell Li-Ion battery protector is used as an example to illustrate the circuit and working principle of the protector. The main features of the device: termination charging voltage is 4.35V, 4.30V and 4.25V (represented by the model suffixes A, B, C respectively), the charging voltage accuracy can reach ±30mV (±0.7%); power consumption is saved at 3.5V The working current is typically 7μA at the working voltage, and the power consumption is only 0.2μA after reaching the termination discharge; there are overcharge, overdischarge, overcurrent protection, and there is a delay to avoid transient interference; the overdischarge voltage is 2.4V, the accuracy is ±3.5%; Small size 5-pin SOT-25 package; operating temperature range -20 to +80 °C.
The application circuit is not complicated, and the circuit is shown in Figure 6. Two P-channel power MOSFETs control charging and discharging respectively. BAT+ and BAT- are connected to the lithium-ion battery. PACK+ and PACK- are the positive and negative terminals of the battery pack, and the DATA terminal is connected to the system. This circuit is suitable for single-cell lithium batteries. If the chip-type components occupy a small space, they can be used in batteries.
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