What are the new functions and working principles of lithium battery protection IC?

The lithium battery has overcharge protection, discharge protection, over current protection and short circuit protection function, lithium battery protection IC, and other new features of protection IC.

A, work principle

1. When charging over current protection

When connect the charger to charge suddenly produced current (e.g., the charger is damaged), over current detection circuit immediately, Cout at this time will be from high to low, power MOSFET from open to cut and realize the protection function.

V-=I&TImes;Rds（on）&TImes;2

(I was charging current;Vdet4, over-current detection voltage, Vdet4-0.1 - V)

2. The lock mode of overcharge

Protection IC during overcharge protection will be after a period of delay time, and then will be cutting the power MOSFET to achieve the purpose of protection, when lithium battery has declined to the lifting point voltage (overcharge hysteresis voltage) will return, at this time and will continue to charge to protect to discharge, charge and discharge. This state will not be able to obtain effectively solve the security problem, the lithium battery will always repeat the charge - discharge - charging and discharging, power MOSFET gate will repeatedly in alternating high and low voltage condition, which could make the MOSFET hot and would also reduce the battery life, so the lock mode is very important. If the lithium electricity protection circuit is detected when overcharge protection lock mode, MOSFET will not heat up, and security is relatively improved a lot.

After the overcharge protection, as long as the charger is connected to the battery pack, will enter the overcharge lock mode at this time. At this point, does not produce rechargeable lithium battery voltage drop, remove the charger and connect the load to restore the state of charge and discharge.

3. Reduce the protection circuit component size

Will delay of charge and short circuit protection with too much integration in to protect IC, capacitor to reduce protection circuit component size.

Second, the requirements for securing protection for IC performance

1. Overcharge protection with high precision

When lithium ion batteries have excessive charging status, in order to prevent due to temperature rise caused by internal pressure rise, must stop charging status. Protection IC will detect the battery voltage, when detected excessive charging, overcharge testing of power MOSFET make the cut off and stop charging. At this point that should be paid attention to are excessive charging voltage of high-precision detection of the, at the time of the battery, a user of the battery to full state is very concern, both to security issues, so you need to be in when allowable voltage by the charging status. To meet the two conditions at the same time, must have the high precision detector, the precision of the current detector for 25 mv, will be subject to further improve the precision.

2. Reduce the protection IC power consumption

B: with the increase of time, has been charged to the lithium ion battery voltage will reduce gradually, and finally to a standard specifications here, right now you need to charge again. If not charging and continue to use, may be caused by excessive discharge and make a battery cannot continue to use. To prevent excessive discharge, protect the IC must detect the battery voltage, once reached excessive discharge detection under voltage, have to make the discharge side of the power MOSFET cut off by the discharge. But the battery itself still has natural discharge and protection IC consumption current existence, so need to make the protection IC consumption to a minimum level of current.

3. Over electric current/short circuit protection should be low testing voltage and high precision requirements

For unknown reasons must immediately stop discharge cause a short-circuit. Over current detection based on power MOSFET Rds (on) for inductive impedance, in order to monitor the voltage drop, if the voltage than ever at this time to stop the discharge current detection voltage is higher. In order to make the power MOSFET Rds (on) valid at the time of charging current and discharge current application, need to make the low impedance value as far as possible, at present the impedance about 20 m Ω ~ 30 m Ω, this current voltage can be lower.

4. Resistant to high voltage

Battery pack and charger connection moment will have high pressure, thus protect the IC should meet the requirements of high voltage.

5. Low battery power

In the protection state, its static electricity flow must be 0.1 mu A little.

6. Zero volt rechargeable

Some in the process of storage battery may put too long, or because the cause of the abnormal cause electricity down to 0 v, so the protection IC needs at 0 v also can realize charging.

Three, protection IC development prospects

As mentioned above, the future protection IC will further improve the precision of the test voltage, reduce the protection IC power flow and improve the misoperation preventing function, at the same time the charger connection terminal of high pressure and the key point of research and development. In terms of packaging, has from leading SOT23-6 SON6 encapsulation, and CSP packaging in the future, even a COB products to satisfy the requirement of the now emphasizes thin and short.

In terms of function, protection IC don't need to integrate all the functions, can be developed according to different lithium battery material single protection IC, such as only the overcharge protection or discharge protection function, it can dramatically reduce the cost and size.

, of course, functional components of single crystal is the same goal, such as mobile phone manufacturers are currently facing will protect IC, charging circuit and power management IC, and other peripheral circuits and logic IC constitute a dual chip chipset, but at the moment, to reduce the open circuit impedance power MOSFET, hard integrate with other IC, even in a particular technology made into single chip, I'm afraid the cost will be high. Therefore, the protection of the single crystal of IC will need some time to solve.

The page contains the contents of the machine translation.