Briefly describe the principle and function of lithium-ion battery protection circuit

　　Ion battery protection circuits include lithium charging protection, over-current/short-circuit protection and over-discharge protection, requiring over-charge protection protection, low IC consumption, high withstand voltage, and volt rechargeability. This text introduces the principle, new function and characteristic requirement of these three kinds of protection circuits in detail.

　　What are the principles and functions of lithium battery protection circuits?

　　Ion battery protection circuits include lithium charging protection, overcurrent/short circuit protection and overdischarge protection, overcharge protection requirements, low IC battery consumption, high withstand voltage, and volt rechargeability. This text introduces the principle, new function and characteristic requirement of these three kinds of protection circuits in detail.

　　More products such as cell phones, PDAs, digital cameras, cell phones, portable audio devices and Bluetooth devices use lithium batteries as their power source. The advantages of batteries and low self-discharge rate. Like nickel batteries and nickel-hydrogen batteries, lithium batteries must consider their safety during charging and discharging to prevent performance degradation. Regarding the overcharge, car discharge, overcurrent and short circuit of the lithium battery, it is very important to design a protection circuit in the battery pack to protect the battery.

　　Due to the high fuel of the lithium ion battery energy battery, the safety of the lithium battery energy battery fuel cell. In the fuel cell battery state, the fuel cell fuel cell energy will generate energy, which stimulates the decomposition of liquid fuel to produce gas, which may cause spontaneous combustion or rupture due to the fuel cell fuel cell boost; on the contrary, in the discharge state, the liquid will decompose. Causes the battery to deteriorate, thereby reducing the number of recharges.

　　The protection circuit of the lithium ion battery is to ensure the safety of the lithium battery charging and discharging state of the battery, and to prevent the deterioration of the characteristics. , When there is mother charging and the charging state is switched to the hanging power to protect the battery, the functions of the protection IC include sponge charging protection, memory charging and over-current/short-circuit protection.

　　Mobile phone charging protection

　　The principle of the battery when charging an external IC is: charging at the same time. In order to prevent the internal pressure from rising due to temperature rise, it is necessary to terminate the charging state. At this time, the protection IC needs to detect the voltage of the battery. When it reaches 4.25V (the overcharge point of the mobile phone battery is 225V), the charging protection is activated, and the MOS is turned on and off, and the battery is charged quickly.

　　In addition, it must be noted that the short-term lactation error cannot be produced due to noise, so it will be overcharged. Therefore, a delay time is required, and the delay time is longer than the duration of the noise.

　　SMS protection

　　In the case of mobile phone text messages, the electrolyte is decomposed and the characteristics are deteriorated, and the number of charging times is reduced.

　　SMS protection SMS IC: SMS call status of the birthday lithium battery, the lithium battery is connected to the upload, and the lithium battery is detected when the lithium battery is placed outside (predicted. 3V will protect the lithium battery from power detection) from on to off. Finally, the battery discharge occurs, and the battery remains in the low-current discharge mode. At this time, the current is only 0.1uA.

　　When the lithium battery is connected, the discharge protection function can only be activated when the battery is connected to the discharge voltage. action.

　　Over current and short circuit current

　　Because of unknown reasons (during safe discharge or being touched by a metal object) prematurely or short-circuit, to ensure safety, the transmission must be stopped immediately.

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

　　Ground, the time that the over-current must occur at the moment of sudden occurrence can also occur at the time of action.

　　Usually after the overcurrent occurs, if the current factor can be removed (for example, immediately separated from the separation), the normal state will be restored, and normal charging and discharging operations can be performed.

　　New functions of lithium battery protection IC

　　In addition to the above-mentioned lithium battery protection IC functions, the following new functions are worthy of attention:

　　1. Overcurrent protection during charging

　　When an overcurrent (such as brain damage) occurs suddenly when the connection is detected for charging, the circuit will immediately discharge the overcurrent, and the discharge will turn from high to low, and the power MOSFET is switched 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 for charging while locked

　　The regular protection IC will pass a period of time during sleep charging protection, and then turn off the power MOSFET for protection purposes. When the lithium voltage has dropped to the charging point (rechargeable battery voltage), then it will continue to charge-protect-discharge- Charge-discharge. This kind of problem will not be effectively solved. The lithium battery will always repeat the action of charging-charging-charging-discharging, and the power MOSFET's ability will be in the state of high and low voltage and therefore will not be in the state, which may cause the MOSFET to heat up, reduce the battery life, and lock Mode is very important. Relatively improved a lot.

　　In the cathodic charge protection, as long as the battery is connected to the battery pack, it will enter the charge lock mode. Even if the voltage of the lithium battery drops, it will not be recharged. It will be removed and connected and connected to resume charging and discharging. status.

　　3. Common protective component size

　　The delay capacitor for lithium charging and short circuit protection is integrated into the protection IC to protect the system component size.

　　Requirements for protecting IC performance

　　1. Focus on charging protection

　　When the lithium-ion battery has the camera charging state, the internal pressure rise caused by the timing charging requires the camera charging state. The IC will detect the battery voltage, and when it detects that the camera is charging, the power MOSFET of the charging detection turns it off and connects to charging. At this time, attention should be paid to the use of the detection voltage of wedding charging, the problem of battery charging to connection, and the safety problem at the same time, so the problem needs to accurately charge the state when the target voltage is reached. To meet these two conditions at the same time, there must be an accurate detector. The current accuracy of the detector is 25mV, and the accuracy will need to be further improved.

　　2. Reduce the power consumption of the protection IC

　　As the use time increases, the voltage of the charged low-power battery will gradually decrease, and finally it will be below the specification standard, and then it needs to be charged. If you continue to use it without charging, it may cause the battery voltage to drop due to discharging and you cannot continue to use it. In order to prevent the sending of short messages, the protection IC must detect the battery. After the detection voltage of the short message is completed, the power MOSFET of the sender can be turned off and sent. But at this time, the battery can discharge naturally and protect the current consumption of the IC, so it is necessary to protect the current consumption of the IC to a minimum.

　　3. Over current/protection requires low detection voltage and short circuit requirements

　　Discharge must be stopped immediately when a short circuit is caused by an unknown reason. Discharge. In order to make the Rds(on) of the power MOSFET effective when applying charging current and discharging current, the value of this parameter needs to be low, so it should be 20mΩ~30mΩ, and the overcurrent detection voltage can be so low.

　　4. High voltage resistance

　　High voltage occurs when the battery pack is connected to the outside world, so the protection IC should meet the requirements of high voltage resistance.

　　5. Low battery consumption

　　In the protection state, its vitality current must be less than 0.1uA.

　　6. Zero volt rechargeable

　　The voltage of individual batteries may be as low as 0V due to prolonged or abnormal reasons during the gathering. Therefore, the protection IC needs to be charged at 0V.

　　Protection IC development prospects

　　In the future, the protection IC will further improve the accuracy of the detection voltage, reduce the current consumption of the protection, and improve the malfunction prevention function. At the same time, the high withstand voltage of the connected IC is also the focus of research.

　　In terms of packaging, SOT23-6 has now generally been switched to SON6 packaging, and there will be C packaging in the future, and even the small light demand provided by the short SP for COB products now appears.

　　In terms of function, the protection IC does not need to put all the functions of the protection integration. A separate protection IC can be developed according to different protection lithium battery materials. For example, only over protection or such functions can greatly reduce the cost and size.

　　Mono-crystalization of functional components is an unchanging goal. For example, the existing mobile phones make protection IC, charging circuit, power management IC and other circuits and logic IC to form a two-chip chipset, but at present, the open circuit of power MOSFET must be reduced. Mosaic is integrated with other ICs, even if a single chip is synthesized with a special technology, I am afraid that the cost will be too high. Therefore, the protection of IC's single crystalization will need to be addressed.