Digital battery

With technological progress and social development, such as mobile phones, laptops, MP3 players, PDAs, handheld game consoles, digital cameras and other portable devices has become increasingly popular, there are many of these products is used in lithium-ion battery-powered, while Because the characteristics of lithium-ion batteries and other rechargeable batteries may be different, usually with an internal circuit, many people do not understand the role of the circuit this article will be the characteristics of lithium-ion Laptop battery and its protection circuit works to develop.

 

Li-ion battery is divided into two types of primary batteries and secondary batteries in some of the lowest power consumption in portable electronic products used primarily in a non-rechargeable lithium batteries, while in laptops, phones phones, PDAs, digital cameras and so on greater energy consumption electronic products use rechargeable secondary batteries, ie lithium-ion battery.

 

And nickel-cadmium and nickel-metal hydride battery compared to lithium-ion batteries have the following advantages:

1, high voltage, single-cell lithium battery voltage to 3.6V Ion, far higher than the nickel-cadmium and nickel-hydride battery voltage of 1.2V metal.

2 volume density, the density of its capacity Ni-MH batteries or nickel-cadmium batteries 1.5-2.5 times.

3, retention of load (eg, a small self-discharge) in place well after the loss of his ability is low.

4, long life, use the normal cycle of life can reach more than 500 times.

5, no memory effect, charging the former did not short-circuiting the remaining capacity, easy to use.

As the chemical properties of lithium-ion IBM ThinkPad R52 battery, under normal use, its internal energy and chemical energy conversion between the positive reaction of chemicals, but in certain circumstances, such as its overload, over discharge and over-current lead to the battery Internal chemical side-reactions, side effects increase, it will seriously affect battery performance and life, and may generate a large number of gas, so that the pressure increases the internal battery soon after the explosion that led to security problems, then all lithium-ion batteries need a protection circuit, used for charging the battery and the condition of the discharge of effective control and under certain conditions, off-line loading and unloading to prevent damage to the battery.

 

The next picture shows a typical lithium-ion battery diagram circuit protection.

 

As indicated above, the road safety cage with two MOSFET (V1, V2) and a control IC (N1) and a number of RC element composition. Control IC is responsible for monitoring the Dell Latitude D830 battery voltage and current loop, and control two MOSFET’s Gate MOSFET switches in the circuit play a role in, respectively, to control the charging circuit and discharge circuit turn on and turn -off, the capacitor C3 for delay, the circuit on the load protection, over-discharge protection, over current protection and short circuit the function of protection, its work principle is as follows:

 

1, the normal state

In normal circuit N1 of the state “CO” and “no” feet high output voltage, two MOSFETs are in a state of conduction, the battery can be free to load and unload, because of MOSFET on - resistance is very low, generally smaller than 30 cents in Europe, so the resistance has little effect on circuit performance.

The protection circuit of the State microA level of current consumption, typically less than 7μA.

 

2, over-charging protection

Requirements of the lithium-ion battery charging method of the constant voltage constant current /, in the initial presentation, a constant current charging and the charging process, increase the voltage to 4.2 V (based on different cathode materials, and some batteries require constant voltage value of 4.1V) for a constant voltage until the current is smaller and smaller.

 

The battery is charging if the charger circuit out of control, will continue after the battery voltage exceeds 4.2 V constant charging current, the battery voltage will continue to increase at this time, when the battery voltage is charged more than 4.3V, the battery chemistry of the side effects will be aggravated and may lead to cell damage or safety problems.

 

In the battery with a protection circuit when the control IC to detect the battery voltage reaches 4.28V (This value for the control IC has decided that a different IC have different values), the “CO” PIN will high voltage variation is zero voltage V2 to the end of his tour on foot, thereby reducing off the charging circuit, so that the battery charger can not charge, played overload protection. V2 comes at a time due to the presence of the diode VD2 body, the hp F4812A battery can discharge the diode external loads.

In the control IC to detect the battery voltage exceeds 4.28V to return the signal between the V2, there is a time delay, the length of delay time is determined by C3, usually set at 1 second or two, to avoid interference caused by false judgments.

 

3, over-discharge protection

The process of discharging the battery on the external load, its voltage will be gradually reduced as the discharge process when the battery voltage to 2.5 V, its capacity has been completely shine, this time the load if the battery continues to discharge, the battery lead to permanent damage.

 

The process of discharging the battery when the control IC to detect the battery voltage drops below 2.3V (the value used by the control IC, IC have various different values), the “DO” PIN will be strong voltage variation is zero voltage, so that V1 amended by the turn-off, reducing outside the discharge circuit so that the battery can no longer discharged into the charges, has been over-discharge protection. V1 comes at a time due to the presence of the body diode VD1, charger through the diode can be charging the battery.

 

Due to over-discharge protection of a state of the sony VGP-BPS2 battery voltage can be reduced, which requires the consumption of the circuit current protection is very weak now control IC enters a low power state, all of the Consumer Protection power circuit is less than 0.1μA.

In the control IC to detect the battery voltage is below 2.3V to send off the signal between the V1, but there is also a time delay, the length of delay time is determined by C3, generally set at 100 milliseconds, to avoid interference from True or False.

 

4, over-current protection

As the chemical properties of lithium-ion battery, the battery manufacturer provides its maximum discharge current should not exceed 2C (C = Battery capacity / hour) when the battery discharge current of more than 2C would cause permanent damage to the battery or the safety problem.

 

Charge the toshiba PA3191U-3BRS battery in the normal discharge process, the discharge current after a series of two MOSFETs, due to MOSFET on resistance, will produce a voltage at its ends, the voltage U = I * 2 * RDS RDS for single MOSFET on resistance, the IC control over the “V” pin of the voltage value for testing, where the load causes an exception for some reason, so that increases in current loop when the loop current is so large that U> 0.1V (the value of the control IC has decided that a different IC have different values), the “DO” PIN will be significant variation in voltage is a zero voltage, so that V1 disabled by the turn-on, cutting off the discharge circuit so that the loop current to zero, to play on-current protection.

In the control IC to detect over-current shutdown has to make between the signals V1, but there is also a time delay, the length of delay time is determined by C3, typically 13 milliseconds to avoid interference caused by false judgments.

In the process of control over, we can see that the value of the size of its over-current detection depends not only on CI control control value, but also depends on the MOSFET on resistance when the MOSFET on resistance, where most of the same control IC, the over-protection during the most value.

 

5, short-circuit protection

The process of discharging the apple A1079 battery to the load, if the loop is so large that U> 0.9 V (the value is determined by the control IC, IC have various different values), the control IC is considered that the load short-circuit the “DO” feet are rapidly changing the high voltage to zero voltage, so that V1 disabled by the turn-on, cutting and discharge circuit, playing short circuit protection. Short-circuit protection, a very short time period, usually less than 7 microseconds. ’s how it works with the methods of over-current protection is similar, but different in determining the length of time protection is not the same.

 

More detailed single-cell lithium battery operates ion protection circuit, multiple-series Lithium-principle of ion battery protection Similarly, will not go above the control circuits used in integrated circuits Series Ricoh R5421 Japan, in the circuit the battery real protection, there are many other types of control IC, such as S-8241 Seiko Japan Series, Japan Series MM3061 MITSUMI, the Taiwan-rich and crystal FS312 series FS313, the Taiwan AAT8632 series of analog technology, and so on, his works very much the same, but some differences in specific settings, some IC controls to safeguard the external circuit, the capacitor filter and the delay of chip capacitors to achieve its peripheral circuits can be very small, like Japan Seiko S-8241 series.

 

In addition to controlling IC circuit there is an important component, is the MOSFET, it acts as a switch in the circuit, because cascade directly between the VGP-BPS9/B battery and the external load, so it’s on the strength of the performance of cells are the impact of MOSFET with a choice of better quality, on-resistance is low, the internal resistance of the battery is low, with a transport capacity is also strong in the exercise of their electricity consumption is also less.

 

With the development of technology, portable devices get smaller and smaller, and as this trend of lithium-ion battery needs protection circuit size are becoming smaller in the last two years have seen the day in the control IC and MOSFET integrated protection of integrated circuit products, such as the series DA7112 dialog, and some manufacturers even the whole package of circuit protection in a small size of the IC, such as product MITSUMI company.

Lithium-ion battery circuit protection includes over-load protection, more protection against overcurrent / short circuit and over-discharge protection, and requires great precision charging protection, protection IC with low power consumption electric volt high-voltage and zero batteries and other features. This paper describes the principle of the three protection circuits, new functions and features required.

 

In recent years, PDAs, digital cameras, cell phones, portable audio devices and Bluetooth products get more and more use of lithium batteries as main power. Li-ion Laptop battery has a small size, high energy density, no memory effect, the high cycle life, high-voltage batteries and the advantages of low self-discharge rate, and nickel-cadmium batteries in nickel metal hydride are not the same lithium batteries must consider the charge and discharge of security so as to prevent deterioration characteristic. To overload the lithium battery, over discharge, over current protection and short-circuit is very important is usually the design of the battery circuit protection to protect Li-ion battery.

 

Because lithium high energy density-ion battery, it is difficult to ensure the safety of the battery. In the most charged, the battery temperature increases after the excess energy, so the decomposition of the electrolyte produced gas because of the internal pressure of the danger arising from the spontaneous combustion or broken on the contrary, over-discharge state, due to the decomposition of the electrolyte causing the Dell Inspiron 5150 battery characteristics and the degradation of sustainability, thus reducing the number of charge cycles.

 

Lithium-ion battery circuit protection is to ensure that this excess charge and discharge state of security and to prevent deterioration characteristic. Lithium-ion battery circuit protection is protected by the CI and structure of two power MOSFETs, including the protection IC for monitoring the battery voltage when there is excessive charges and the discharge state to pass the order to fill the power MOSFET to protect the battery, protect the functions of the IC during the load protection, over-discharge protection and protection against overcurrent / short circuit.

 

1, an overload protection

 

The principle of over-charge protection IC as follows: When an external charger for lithium battery, when, to avoid a temperature rise caused by increased internal pressure must end the state of load. At this stage, the need to test the hp 417066-001 battery voltage to protect IC when the time comes to 4.25V (assuming that the point of overcharging 4.25V) which activate the over-load protection, the MOSFET power to cut through the opening and closing the load.

 

In addition, attention must also be the result of excessive noise generated by the perception of dysfunction detected if determined to be overload protection. Therefore, the need to adjust the delay and time delay can be shorter than the noise.

 

2, over-discharge protection

 

In the case of excessive discharge, the decomposition of the electrolyte in case of damage caused by the characteristics of the battery and cause a reduction in the number of charge cycles. Protection of lithium-IC with on-rejection phenomenon can be avoided to protect the battery.

 

Over-the principle of discharge protection IC: To avoid excessive sony VGP-BPS2A battery status at discharge, assuming that the lithium battery connected to the load when the voltage of the lithium battery is less than the highest - point of discharge voltage detection (assumed to be 2.3V) will activate the over-discharge protection, so that the power MOSFET transition from open-cut and the threshold of discharge, to avoid battery-phenomenon discharge, and keep the battery low quiescent current in standby mode, yet current 0.1μA.

 

When the lithium battery is connected to the charger and the battery voltage lithium is greater than this period of excessive discharge voltage, over-discharge protection is lifted. In addition, taking into account the conditions of discharge pulse, excessive discharge detection circuit with time delay to prevent malfunction.

 

3, the current and short-circuit current

 

For unknown reasons (discharge or negative by metallic objects inadvertently) caused by over-current circuit or short to ensure security, you should immediately cease its discharge.

 

Terms runway Principles of protection against overcurrent IC, when the discharge toshiba PA3399U-1BAS battery current is too large or too short occurs, the protection IC is turned off (short circuit) current protection, over current detection at the moment is to power MOSFET’s Rds (on) as a sensor monitoring the impedance voltage drop in the case, if the ratio set by the voltage-current detection is higher when the discharge stopped, the formula is:

V = I × Rds (on) × 2 (V-for over-current detection voltage, I is discharge current)

Suppose V = 0.2V, Rds () = 25mΩ, and protect the current size of I = 4A on

Similarly, too much time current detection delay should also be provided to prevent current flow generated when there are unexpected failures.

Usually, after the election of overheating if they can remove the excess current factors (such as the charge immediately and out) will resume its normal state, may proceed with the normal load, the discharge action.

 

4 new protection features of the lithium-IC’s

 

In addition to the protection feature of the lithium IC attention the following new battery features is also interesting:

a. Charging over-current protection

When connecting the charger suddenly aware (as the charger is damaged), on-circuit current detection immediately, this time from top to bottom Court, the MOSFET power to cut the open position for protection.

V = I × Rds () × 2

(I is the load current; Vdet4 on voltage-current detection, Vdet4 to-0.1V)

 

b. Overcharge when the lock mode

Usually protect the IC in the over-charging protection will be after a period of delay time, and then it will cut the power MOSFETs to achieve the goal of protection when the battery voltage lithium dropped in points Lifting (hysteresis voltage overload), when it will resume once again continue to impose protection →Discharge charge discharge. Security issues in this state will not be able to get an effective solution, lithium batteries will always repeat the charge discharge →Action load discharge gate MOSFET power will be repeated alternately at high and low voltage state, which could make the MOSFET heater but it also reduces the battery life, if the lock mode is very important. If the circuit of the lithium battery protection detects over-protection mode load locked, IC will not get hot, and the relative security has improved considerably.

In the over-load protection, simply plug the battery charger, the charging time will be entered into lock mode. At this stage, even if the voltage drops of the lithium battery can not produce the recharge of the situation, remove and connect to load and unload the load can be restored condition.

 

c. Reduce the size of the circuit protection component

Will overload and short circuit protection with an integrated capacitor delay for the protection of the IC inside to reduce the size of circuit protection components?

 

5, the protection requirements of IC performance

 

a. Overload protection, high accuracy

When the lithium-ion battery charging excessive state to avoid a temperature rise caused by increased internal pressure required for the threshold state of charge. Protection IC detects the cbattery voltage, when the overcharge is detected, then detection of over-charging power MOSFETs in order to cut the load threshold. At this point should be noted that over-voltage detection burden of high precision, battery charging, battery to a state is a danger of the user, taking into account security issues and should enable the voltage when the threshold state of charge. To simultaneously satisfy these two conditions, there must be a detector of high precision, accuracy of 25mV current detector, the accuracy will be improved.

 

b. In order to reduce IC power consumption to protect

With the increasing use of time was enough lithium power-voltage ion battery will gradually diminish the value of the last low specifications below, this time need to recharge. If you do not charge for continued use, may lead to excessive battery discharge Ershi is not used. To avoid too much discharge protection IC to detect the battery voltage, over-voltage detection of the landfill once they reach the following, you must cut the discharge of MOSFET power and the threshold discharge. But this time, the BATCL50L battery itself, there are still protecting the natural discharge and IC current consumption exist, therefore the need to protect the IC power consumption to a minimum.

 

c. Protection against overcurrent / short-circuit the need for low-voltage detection and precision requirements

Short circuits due to unknown causes must immediately stop selling them. Over-current detection is based on power MOSFET RDS (on) for the impedance of induction to follow the voltage drop of blood at the time when compared with a voltage-current detection is also high at namely, to stop selling them. To MOSFET’s Rds (on) in the current charge and discharge current is the effective use of time is needed for the impedance as low as possible, at present the impedance is approximately 20mΩ ~ 30mΩ, if the voltage-current detection may be lower.

 

d. Resistant to high voltage

Battery and charger to connect the instant the pressure will be generated if the protection must meet the requirements of high voltage IC.

 

e. Low VGP-BPS2B battery consumption

In the protection of the state, its current consumption of 0.1μA rest must be small.

 

f. Zero-Volt Rechargeable

Some batteries may be stored in the process because it takes too long or unusual causes of tension as low as 0V, and therefore need to protect the IC can be achieved when 0V load.

 

6, the protection IC Prospect

 

As mentioned previously, the future protection of integrated circuits should further enhance the detection voltage accuracy and reduce current consumption to protect and improve the CI function to prevent malfunctions and so on, and the charger to connect the terminal High voltage is also the focus of research and development. In the package, at present has been a gradual shift SOT23-6 package SON6 the future, there are CSP package, even COB products to meet the requirements highlighted in a word, light.

 

In functions, protect the IC does not require integration of all functions, according to different materials, to develop a single lithium Dell Latitude D830 battery protection IC, the coverage only if overloaded or over-discharge protection, which can significantly reduce the cost and size.

 

Of course, the functional components is a single crystal of the same goals, such as manufacturers of mobile phones today have been directed towards protecting the IC, charging circuit and power management IC, and other peripheral circuits and logic is a two chip chipset, but rather of power MOSFET’s open reduction of impedance of the circuit is difficult to integrate with other IC, even if it is made of a special single-chip technology, I fear the cost is too high. Therefore, protection of single crystal integrated circuits should take some time to resolve.