How do you activate lithium-ion battery protection board?

The protection function of lithium-ion battery is usually completed by protection circuit board and current device like PTC. Protection board is composed of electronic circuits, voltage of battery core and charging & discharging circuit at accurately monitored at -40°C to +85 ° C environment. Control the current circuit on and off; PTC in high temperature environment to prevent battery damage.

Ordinary lithium battery protection boards usually include control ICs, MOS switches, resistors, capacitors, and auxiliary devices FUSE, PTC, NTC, ID, memory, and so on. The control IC controls the MOS switch to turn on under all normal conditions, so that the cell and the external circuit turned on, and when the cell voltage or the loop current exceeds a prescribed value, it immediately controls the MOS switch to turn off, and protects the cell. Safety.

When the protection board is normal, Vdd is high level, Vss, VM is low level, DO and CO are high level. When any parameter of Vdd, Vss, VM is changed, the level of DO or CO will be A change has occurred.

Principle of Lithium-ion battery protection board

The reason why lithium batteries (fillable) need protection determined by its own characteristics. Because the material of the lithium battery itself determines that it cannot overcharged, over discharged, overcurrent, short circuited and ultra-high temperature charge and discharge, the lithium battery lithium battery assembly will always follow an exquisite protection board and a current fuse.

The protection circuit board and the current device such as the PTC usually complete the protection function of the lithium battery. The protection board is composed of electronic circuits, and the voltage of the battery core and the charging and discharging circuit accurately monitored at -40 ° C to +85 ° C environment. Current, timely control of the current circuit on and off; PTC in the high temperature environment to prevent battery damage.

Ordinary lithium battery protection boards usually include control ICs, MOS switches, resistors, capacitors, and auxiliary devices FUSE, PTC, NTC, ID, memory, and so on. The control IC controls the MOS switch to turn on under all normal conditions, so that the cell and the external circuit are turned on, and when the cell voltage or the loop current exceeds a prescribed value, it immediately controls the MOS switch to turn off, and protects the cell. Safety.

Detailed analysis of the principle of lithium-ion battery protection board

When the protection board is normal, Vdd is high level, Vss, VM is low level, DO and CO are high level. When any parameter of Vdd, Vss, VM is changed, the level of DO or CO will be A change has occurred.

1. Overcharge detection voltage: In the normal state, Vdd gradually rises to the voltage between VDD and VSS when the CO terminal changes from a high level to a low level.

2. Overcharge release voltage: In the state of charge, Vdd gradually decreases to the voltage between VDD and VSS when the CO terminal changes from low level to high level.

3. Over discharge detection voltage: In the normal state, Vdd gradually decreases to the voltage between VDD and VSS when the DO terminal changes from a high level to a low level.

4. Over discharge release voltage: In the over discharge state, Vdd gradually rises to the voltage between VDD and VSS when the DO terminal changes from low level to high level.

5. Overcurrent 1 detection voltage: In the normal state, the VM gradually rises to the voltage between VM and VSS when DO changes from high level to low level.

6. Overcurrent 2 detection voltage: In the normal state, the VM rises from OV at a speed of 1 ms or more and 4 ms or less to the voltage between VM and VSS when the DO terminal changes from a high level to a low level.

7. Load short-circuit detection voltage: In the normal state, the VM rises at a speed of 1 μS or more and 50 μS or less from OV to the voltage between VM and VSS when the DO terminal changes from a high level to a low level.

8. Charger detection voltage: In the over discharge state, the VM gradually drops to OV and the voltage between VM and VSS when the DO changes from low level to high level.

9. Current consumption during normal operation: In the normal state, the current flowing through the VDD terminal (IDD) is the current consumption during normal operation.

10. Over-discharge current consumption: In the discharge state, the current flowing through the VDD terminal (IDD) is the over-current discharge current consumption.

Typical lithium-ion battery protection circuit

Due to the chemical characteristics of lithium batteries, during normal use, the internal chemical reaction of electrical energy and chemical energy is mutually converted, but under certain conditions, such as overcharging, over discharging and overcurrent, the internal battery will caused. Chemical side reactions occur, which will seriously affect the performance and service life of the battery, and may generate a large amount of gas, causing the internal pressure of the battery to rapidly increase and explode, resulting in safety problems. Therefore, all lithium batteries require a protection. The circuit used for effectively monitoring the charging and discharging states of the battery, and shutting down the charging and discharging circuits under certain conditions to prevent damage to the battery.

The figure below shows a typical lithium-ion battery protection circuit schematic.

Detailed analysis of the principle of lithium-ion battery protection board

As shown in the figure above, the protection loop consists of two MOSFETs (V1, V2) and a control IC (N1) plus some RC components. The control IC is responsible for monitoring the battery voltage and the loop current, and controlling the gates of the two MOSFETs. The MOSFET functions, as a switch in the circuit to control the conduction and shutdown of the charging circuit and the discharging circuit, respectively, and C3 is a delay capacitor. With overcharge protection, over-discharge protection, over-current protection and short-circuit protection, its working principle is as follows:

1, normal state

In the normal state, the "CO" and "DO" pins of N1 output high voltage in the circuit, both MOSFETs are in conduction state, and the battery can be freely charged and discharged. Since the on-resistance of the MOSFET is small, it is usually smaller. 30 milliohms, so its on-resistance has little effect on the performance of the circuit. The current consumption of the protection circuit in this state is μA level, usually less than 7μA.

2, overcharge protection

Lithium-ion batteries require a constant current/constant voltage. In the initial stage of charging, they charged at a constant current. As the charging process, the voltage rises to 4.2V (depending on the cathode material, some batteries require a constant voltage of 4). .1V), turn to constant voltage charging until the current is getting smaller and smaller. When the battery charged, if the charger circuit loses control, the battery voltage will exceed 4.2V and continue constant current charging. At this time, the battery voltage will continue to rise. When the battery voltage charged to over 4.3V, the battery the chemical side reactions will increase, causing battery damage or safety problems. In a battery with a protection circuit, when the control IC detects that the battery voltage reaches 4.28V (this value is determined by the control IC and different ICs have different values), the "CO" pin will change from a high voltage to a zero voltage. V2 turned from on to off, thus cutting off the charging circuit, so that the charger can no longer charge the battery, which acts as an overcharge protection. At this time, due to the presence of the body diode VD2 that provided by the V2, the battery could discharge the external load through the diode. There is a delay time between when the control IC detects that the battery voltage exceeds 4.28V and when the V2 signal turned off. The length of the delay time determined by C3, usually set to about 1 second to avoid interference. Misjudgment.

3, short circuit protection

When the battery is discharging to the load, if the loop current so large U>0.9V (this value is determined by the control IC and different ICs have different values. The control IC determines that the load is short-circuited, and its "DO" pin It will quickly change from a high voltage to a zero voltage, turning V1 from on to off, thus cutting off the discharge loop and providing short-circuit protection. The short-circuit protection has a very short delay time, usually less than 7 microseconds. The working principle is similar to the overcurrent protection, except that the judgment method is different, and the protection delay time also different. In addition to the control IC, there is another important component in the circuit, the MOSFET, which acts as a switch in the circuit. Since it directly connected between the battery and the external load, its on-resistance has a performance on the battery. The effect is that when the selected MOSFET is better, its on-resistance is small, the internal resistance of the battery pack is small, the load carrying capacity is also strong, and the power consumed during discharge small.

4, over current protection

Due to the chemical characteristics of lithium-ion batteries, battery manufacturers stipulate that their discharge current should not exceed 2C (C=battery capacity/hour). When the battery exceeds 2C current discharge, it will cause permanent damage or safety problems. During normal discharge of the battery, the discharge current passed through two MOSFETs in series. Due to the on-resistance of the MOSFET, a voltage generated across the MOSFET. The voltage value U=I*RDS*2, RDS is a single MOSFET on-resistance, the "V-" pin on the control IC detects the voltage value. If load is abnormal due to some reason, the loop current increases, and the loop current is so large that U>0.1V (this value). When the control IC determines that different ICs have different values, the "DO" pin will be converted from a high voltage to a zero voltage, turning V1 from on to off, thereby cutting off the discharge loop and making the current in the loop zero. It acts as an overcurrent protection. There is also a delay between when the control IC detects an overcurrent and when the V1 signal turned off. The length of the delay determined by C3, usually about 13 milliseconds, to avoid misjudgment caused by interference. In the above control process, the overcurrent detection value depends not only on the control value of the control IC, but also on the on-resistance of the MOSFET. When the MOSFET on-resistance is larger, the over-current protection applied to the same control IC. The smaller the value.

5, over discharge protection

When battery discharged to external load, its voltage will gradually decrease with discharge process. When battery voltage drops to 2.5V, its capacity has b completely discharged. During this time if battery continues to discharge load, it will cause battery permanent damage. During battery discharge, when control IC detects that battery voltage is lower than 2.3V (this value is determined by control IC, different ICs have different values). Its "DO" pin will converted from a high voltage to a zero voltage, and V1 turns from on to off, which cuts off discharge circuit, so that battery can no longer discharge load and protects against over discharge. Due to presence of V1 body diode VD1, charger can charge battery through the diode. Since battery voltage can no longer lowered under the over-discharge protection state, current consumption of protection circuit is required to be extremely small. Therefore, the control IC will enter a low-power state, and entire protection circuit consumes less than 0.1 μA. There is also a delay time between control IC detects the battery voltage is lower than 2.3V and V1 signal turned off. The length of delay time determined by C3, usually set to about 100 milliseconds to avoid interference misjudgment

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