CR2032 battery

　　How does a CR2032 batterycircuit work? See how the actual theory is analyzed!

　　CR2032 batterycircuit working principle The circuit has overcharge protection, over-discharge protection, over-current protection and short-circuit protection functions. Its working principle is analyzed as follows:

　　1. Normal state: In the normal state, the CO and DO pins of N1 in the circuit both output high voltage, and both MOSFETs are in the on state. The CR2032 batterycan charge and discharge freely. Since the on-resistance of the MOSFET is very small, usually less than 30 milliohms, so its on-resistance has little impact on the performance of the circuit. 7|The current consumption of the protection circuit in this state is μA level, usually less than 7μA.

　　2. The charging method required for overcharge protection lithium-ion batteries is constant current/constant voltage. In the early stage of charging, constant current charging is used. As the charging process progresses, the voltage will rise to 4.2V (depending on the positive electrode material, some batteries require constant current (voltage value is 4.1V), switch to constant voltage charging until the current becomes smaller and smaller. During the charging process of the battery, if the charger circuit loses control, the CR2032 batteryvoltage will continue to be charged with constant current after it exceeds 4.2V. At this time, the CR2032 batteryvoltage will continue to rise. When the CR2032 batteryvoltage is charged to exceed 4.3V, the CR2032 batterychemistry will Side reactions will be aggravated, causing CR2032 batterydamage or safety issues.

　　In a CR2032 batterywith a protection circuit, when the control IC detects that the CR2032 batteryvoltage reaches 4.28V (this value is determined by the control IC, different ICs have different values), its CO pin will change from high voltage to zero voltage, causing V2 It switches from on to off, thus cutting off the charging circuit and making the charger no longer able to charge the battery, thus serving as overcharge protection. At this time, due to the existence of the body diode VD2 of V2, the CR2032 batterycan discharge the external load through this diode. There is still a delay time between when the control IC detects that the CR2032 batteryvoltage exceeds 4.28V and sends the shutdown V2 signal. The length of this delay time is determined by C3 and is usually set to about 1 second to avoid errors caused by interference. judge.

　　3. Over-discharge protection When the CR2032 batterydischarges to the external load, its voltage will gradually decrease with the discharge process. When the CR2032 batteryvoltage drops to 2.5V, its capacity has been completely discharged. At this time, if the CR2032 batterycontinues to discharge the load , will cause permanent damage to the battery. During the CR2032 batterydischarge process, when the control IC detects that the CR2032 batteryvoltage is lower than 2.3V (this value is determined by the control IC, different ICs have different values), its DO pin will change from high voltage to zero voltage, causing V1 to switch from conductor to Turning on to off, thus cutting off the discharge circuit, making the CR2032 batteryno longer able to discharge the load, thus playing the role of over-discharge protection. At this time, due to the existence of the body diode VD1 of V1, the charger can charge the CR2032 batterythrough this diode.

　　Since the CR2032 batteryvoltage cannot be reduced in the over-discharge protection state, the current consumption of the protection circuit is required to be extremely small. At this time, the control IC will enter a low power consumption state, and the power consumption of the entire protection circuit will be less than 0.1μA. There is also a delay time between the control IC detecting that the CR2032 batteryvoltage is lower than 2.3V and sending the shutdown V1 signal. The length of this delay time is determined by C3 and is usually set to about 100 milliseconds to avoid errors caused by interference. judge.

　　4. Over-current protection Due to the chemical characteristics of lithium-ion batteries, the CR2032 batterymanufacturer stipulates that the maximum discharge current cannot exceed 2C (C=CR2032 batterycapacity/hour). When the CR2032 batteryis discharged with a current exceeding 2C, it will cause permanent damage to the battery. or security issues arise. During the normal discharge process of the CR2032 batteryto the load, when the discharge current passes through two MOSFETs connected in series, a voltage will be generated at both ends due to the on-resistance of the MOSFETs. The voltage value U=I*RDS*2, RDS is a single MOSFET conduction resistance, the V- pin on the control IC detects the voltage value. If the load is abnormal for some reason, the loop current increases. When the loop current is large enough to make U>0.1V (this value is determined by the control IC (determined (different ICs have different values)), its DO pin will change from high voltage to zero voltage, causing V1 to turn from on to off, thereby cutting off the discharge circuit, making the current in the circuit zero, and causing overcurrent Protective effects.

　　There is also a delay time between the control IC detecting the occurrence of overcurrent and sending the shutdown V1 signal. The length of this delay time is determined by C3, usually about 13 milliseconds, to avoid misjudgment caused by interference. From the above control process, it can be seen that the overcurrent detection value not only depends on the control value of the control IC, but also depends on the on-resistance of the MOSFET. When the on-resistance of the MOSFET is larger, for the same control IC, the over-current protection The smaller the value.

　　5. When the short-circuit protection CR2032 batterydischarges the load, if the loop current is large enough to make U>0.9V (this value is determined by the control IC, different ICs have different values), the control IC will judge that the load is short-circuited, and its DO The pin will quickly change from high voltage to zero voltage, causing V1 to turn from on to off, thus cutting off the discharge circuit and playing a role in short-circuit protection. The delay time of short circuit protection is very short, usually less than 7 microseconds. Its working principle is similar to overcurrent protection, but the judgment method is different and the protection delay time is also different.

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