502030 battery

Detailed introduction to the principles, new functions and characteristic requirements of the three protection circuits for 502030 battery

Lithium-ion battery protection circuits include overcharge protection, overcurrent/short circuit protection and over-discharge protection, requiring high-precision overcharge protection, low power consumption of protection IC, high withstand voltage and zero-volt rechargeable characteristics. This article introduces the principles, new functions and characteristic requirements of these three protection circuits in detail.

In recent years, more and more products such as PDAs, digital cameras, mobile phones, portable audio devices and Bluetooth devices use 502030 battery as the main power source. 502030 battery have the advantages of small size, high energy density, no memory effect, high cycle life, high voltage battery and low self-discharge rate. Unlike nickel-cadmium and nickel-metal hydride batteries, 502030 battery must consider safety during charging and discharging to prevent characteristic degradation. Overcharge, over-discharge, overcurrent and short-circuit protection for 502030 battery are very important, so protection circuits are usually designed in the battery pack to protect 502030 battery.

Due to the high energy density of lithium-ion batteries, it is difficult to ensure the safety of batteries. In the overcharge state, the battery temperature rises and the energy becomes excessive, so the electrolyte decomposes and produces gas, and the internal pressure rises, which may cause spontaneous combustion or rupture. On the contrary, in the over-discharge state, the electrolyte decomposes, causing the battery characteristics and durability to deteriorate, thereby reducing the number of recharges. The protection circuit of lithium-ion batteries is to ensure the safety of such over-charge and discharge states and prevent the characteristics from deteriorating. The protection circuit of lithium-ion batteries is composed of a protection IC and two power MOSFETs. The protection IC monitors the battery voltage and switches to an external power MOSFET to protect the battery when there is an over-charge and discharge state. The functions of the protection IC include over-charge protection, over-discharge protection, and over-current/short-circuit protection.

Over-charge protection

The principle of the over-charge protection IC is: when the external charger charges the lithium battery, in order to prevent the internal pressure from rising due to the temperature rise, the charging state needs to be terminated. At this time, the protection IC needs to detect the battery voltage. When it reaches 4.25V (assuming that the battery over-charge point is 4.25V), the over-charge protection is activated, and the power MOS is turned from on to off, thereby stopping the charging. In addition, attention must be paid to the overcharge detection misoperation caused by noise to avoid judging it as overcharge protection. Therefore, a delay time needs to be set, and the delay time cannot be shorter than the duration of the noise.

Over-discharge protection

In the case of over-discharge, the electrolyte decomposes, causing the battery characteristics to deteriorate and resulting in a reduction in the number of charging times. The use of lithium battery protection IC can avoid over-discharge and realize the battery protection function.

Principle of over-discharge protection IC: In order to prevent the over-discharge state of 502030 battery, assuming that the lithium battery is connected to a load, when the lithium battery voltage is lower than its over-discharge voltage detection point (assuming it is 2.3V), the over-discharge protection will be activated, causing the power MOSFET to turn from on to off and cut off the discharge to avoid over-discharge of the battery, and keep the battery in a low quiescent current standby mode, at which the current is only 0.1uA.

When the lithium battery is connected to a charger and the lithium battery voltage is higher than the over-discharge voltage, the over-discharge protection function can be released. In addition, considering the pulse discharge situation, the over-discharge detection circuit is provided with a delay time to avoid misoperation.

Overcurrent and short-circuit current

Overcurrent or short circuit caused by unknown reasons (discharging or positive and negative poles accidentally touched by metal objects), to ensure safety, the discharge must be stopped immediately.

The principle of overcurrent protection IC is that when the discharge current is too large or a short circuit occurs, the protection IC will activate the over (short circuit) current protection. At this time, the overcurrent detection is to use the Rds (on) of the power MOSFET as an inductive impedance to monitor the voltage drop. If it is higher than the set overcurrent detection voltage, the discharge is stopped. The calculation formula is: V-=I×Rds (on)×2 (V- is the overcurrent detection voltage, I is the discharge current). Assuming V-=0.2V, Rds (on)=25mΩ, the protection current is I=4A.

Similarly, overcurrent detection must also have a delay time to prevent false operation when a sudden current flows in. Usually after an overcurrent occurs, if the overcurrent factor can be removed (for example, immediately disconnecting from the load), it will return to its normal state and normal charging and discharging can be performed again.

New functions of lithium battery protection IC

In addition to the above-mentioned lithium battery protection IC functions, the following new functions are also worth paying attention to:

1. Overcurrent protection during charging: When an overcurrent suddenly occurs when the charger is connected for charging (such as a damaged charger), the circuit immediately performs overcurrent detection. At this time, Cout will change from high to low, and the power MOSFET will change from on to off to achieve the protection function. V-(Vdet4 overcurrent detection voltage, Vdet4 is -0.1V) = I (charging current) × Rds (on) × 2

2. Lock mode during overcharging: Usually, the protection IC will go through a delay time during overcharging protection, and then turn off the power MOSFET to achieve the purpose of protection. When the lithium battery voltage drops to the release point (overcharging hysteresis voltage), it will recover, and then it will continue to charge-protect-discharge-charge-discharge. The safety problem of this state cannot be effectively solved. The lithium battery will keep repeating the action of charge-discharge-charge-discharge, and the gate of the power MOSFET will repeatedly be in a high and low voltage alternating state, which may make the MOSFET hot and reduce the battery life, so the lock mode is very important. If the lithium battery protection circuit has a lock mode when detecting overcharge protection, the MOSFET will not get hot and the safety is relatively improved.

After the overcharge protection, as long as the charger is connected to the battery pack, it will enter the overcharge lock mode. At this time, even if the lithium battery voltage drops, it will not be recharged. Removing the charger and connecting the load can restore the charge and discharge state.

3. Reduce the size of the protection circuit components

Integrate the delay capacitor for overcharge and short circuit protection into the protection IC to reduce the size of the protection circuit components

Requirements for the performance of the protection IC

1. High precision of overcharge protection

When the lithium-ion battery is overcharged, the charging state must be cut off to prevent the internal pressure from rising due to temperature rise. The protection IC will detect the battery voltage. When overcharge is detected, the power MOSFET of the overcharge detection turns it off and cuts off the charging. At this time, it should be noted that the overcharge detection voltage should be highly accurate. When charging the battery, charging the battery to a full state is a problem that users are very concerned about. At the same time, safety issues are taken into account, so it is necessary to cut off the charging state when the allowable voltage is reached. To meet these two conditions at the same time, a high-precision detector is required. The current detector has an accuracy of 25mV, and this accuracy needs to be further improved.

2. Reduce the power consumption of the protection IC

With the increase of usage time, the voltage of the charged lithium-ion battery will gradually decrease, and finally fall below the standard value of the specification. At this time, it needs to be recharged. If it continues to be used without charging, it may cause the battery to be unusable due to over-discharge. To prevent over-discharge, the protection IC must detect the battery voltage. Once it reaches below the over-discharge detection voltage, the power MOSFET on the discharge side must be turned off to stop the discharge. However, at this time, the battery itself still has natural discharge and the consumption current of the protection IC, so the current consumed by the protection IC needs to be minimized.

3. Over-current/short-circuit protection requires low detection voltage and high accuracy. When a short circuit occurs due to unknown reasons, the discharge must be stopped immediately. The over-current 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 over-current detection voltage, the discharge is stopped. In order to effectively apply the Rds(on) of the power MOSFET during charging and discharging currents, the impedance value needs to be as low as possible. Currently, the impedance is about 20mΩ~30mΩ, so that the overcurrent detection voltage can be lower.

4. When the high-voltage 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. When the low battery power consumption is in the protection state, its static current consumption must be less than 0.1uA.

6. Zero-volt rechargeable Some batteries may cause the voltage to drop to 0V during storage due to too long or abnormal reasons, so the protection IC needs to be able to charge at 0V.

Development prospects of protection IC

As mentioned above, in the future, the protection IC will further improve the accuracy of the detection voltage, reduce the current consumption of the protection IC, and improve the malfunction prevention function. At the same time, the high withstand voltage of the charger connection terminal is also the focus of research and development.

In terms of packaging, it has gradually shifted from SOT23-6 to SON6 packaging. In the future, there will be CSP packaging, and even COB products will appear to meet the requirements of lightness, thinness and shortness emphasized now. 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 over-discharge protection function, which can greatly reduce the cost and size.

Of course, the single crystal of functional components is an unchanging goal. For example, mobile phone manufacturers are currently moving towards a dual-chip chipset consisting of protection IC, charging circuit, power management IC and other peripheral circuits and logic IC. However, it is difficult to integrate with other ICs to reduce the open-circuit impedance of power MOSFET. Even if a single chip is made with special technology, the cost may be too high. Therefore, it will take some time to solve the single crystal of protection IC.

With the increasing popularity of mobile services, China has reached an average of 64.4 mobile phones per 100 people, and coastal developed cities such as Shanghai and Beijing have an average of 1.2 mobile phones per person. Although mobile phones have become a necessity for most people, do you really know how to maintain your mobile phone battery? Doing the following ten points will extend the service life of your mobile phone battery.

1. If the battery of a newly purchased mobile phone is a lithium battery, the first 3-5 charges are generally called the adjustment period, and should be charged for more than 14 hours to ensure that the activity of lithium ions is fully activated. Lithium-ion batteries have no memory effect, but they are very inert. They should be fully activated to ensure that they can achieve the best performance in the future.

2. Before the battery leaves the factory, the manufacturer has activated it and pre-charged it, so the new batteries you buy have surplus power. Generally, the manufacturer will charge the battery according to the adjustment period, but the standby is still seriously insufficient. Assuming that the purchased battery is genuine, in this case, the adjustment period should be extended and 3-5 full charge and discharge should be performed.

3. When charging with a fast charger, when the indicator light changes, it generally only indicates that it is 90% full, so it is not recommended. The charger will automatically change to slow charging to fill the battery. It is best to use the battery after it is fully charged, otherwise it will shorten the use time.

4. Before charging, 502030 battery do not need to be discharged specifically. Improper discharge will damage the battery. When charging, try to charge slowly and reduce fast charging. The time should not exceed 24 hours. After 3-5 full charge and discharge cycles, the chemical substances inside the battery will be fully "activated" to achieve the best use effect.

5. Please use the original charger or a reputable brand charger. 502030 battery should use a special charger for 502030 battery and follow the instructions, otherwise the battery will be damaged or even dangerous.

6. Lithium-ion batteries must use a special charger, otherwise they may not reach saturation and affect their performance. After charging, avoid placing them on the charger for more than 12 hours, and separate the battery and the phone when not in use for a long time.

7. Many users often turn on their phones while charging, which actually harms the life of the phone. Because during the charging process, the circuit board of the phone will heat up. If there is an incoming call at this time, it may generate instantaneous reflux current and damage the internal parts of the phone.

8. The life of the battery depends on the number of repeated charging and discharging, so you should try to avoid charging when the battery has residual power, which will shorten the battery life. If the phone is turned off for more than 7 days, the phone battery should be fully discharged first and then used after it is fully charged.

9. Mobile phone batteries all have self-discharge. When not in use, nickel-hydrogen batteries will discharge about 1% of the remaining capacity every day, and 502030 battery will discharge 0.2%-0.3% every day. When charging the battery, try to use a dedicated socket and do not share the socket between the charger and the TV or other home appliances.

10. Do not expose the battery to high temperatures or severe cold. For example, during the dog days of July and August, do not leave the phone in the car exposed to the scorching sun; or take it to an air-conditioned room and place it in a place where the air conditioning blows directly. It is normal for the battery to be a little hot when charging, but it cannot be left directly in a high temperature environment. To avoid this, it is best to charge at room temperature and do not cover the phone with anything.

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