New functions of lithium battery protection IC

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New functions of lithium battery protection IC :

In addition to the above-mentioned lithium battery protection IC functions , there are some new functions that deserve our attention . Take the "Ricoh" lithium battery protection IC exclusively represented by Dongrui Electronics as an example --- R5426

(1) Overcurrent protection during charging :

When an overcurrent suddenly occurs during charging ( charger damage ), overcurrent detection occurs during charging . At this time , Cout will be changed from High to Low, and Power MOS will be changed from ON to OFF to achieve protection action .

V-(Vdet4 overcurrent detection voltage ) = I( charging current )*Rds(on)*2

Note : Vdet4 is -0.1V

(2) Shorten the test time :

Assuming that it takes 1 second to test one PCB , then 1 million PCBs will take 1 million seconds , which is very time-consuming and inefficient . Therefore, we can use the following functions to shorten the test time .

(A) When we open the DS pin of R5426 , the delay time is as shown in the specification.

(B) When we connect the DS pin of R5426 to VDD , the delay time will be only 1/90.

(C) When we connect the DS pin of R5426 to Vim (min=1.2V, max=VDD-1.1V), the delay time can be ignored.

(3) Overcharge lock mode (Latch):

Usually, the protection IC will turn off the Power MOS (Cout) after a delay time during overcharge protection to achieve the purpose of protection . When the lithium battery voltage drops to the release point (Overcharge Hysteresis Voltage) , it will recover . At this time, it will continue to charge , protect , and discharge . This situation is not a good situation and the safety problem cannot be effectively solved .

Lithium batteries are constantly charging and discharging , and the gate of the Power MOS will repeatedly switch between High and Low. This may cause the MOSFET to heat up and also affect the battery life . This shows the importance of Latch Mode .

If the lithium battery protection circuit has a latch mode when detecting overcharge protection , the MOSFET will not get hot and the safety will be much improved .

After overcharge protection is detected , as long as the charger is connected to the battery pack , the current state and the overcharge lock mode are reached . Therefore , although the voltage of the lithium battery drops , recharging will not occur . To resolve this situation , just remove the charger and connect the load to restore the charge and discharge state.

(4) Reduce the size of protection circuit components :

The delay capacitor for overcharge and short circuit protection is built into the protection IC

Requirements for protecting IC :

(A) High precision of overcharge protection :

When a lithium-ion battery is overcharged, the charging state must be turned off to prevent the internal pressure from rising due to temperature rise. This protection IC checks the battery voltage. When overcharging is detected, the overcharge detection Power-MOSFET is turned OFF to cut off the charging. At this time, it should be noted that the overcharge detection voltage should be highly accurate. When charging the battery, it is a problem that users are very concerned about charging the battery to a full state. At the same time, in order to take into account the safety issue, the charging state must be cut off when the allowable voltage is reached. To meet these two conditions at the same time, a very high-precision detector is required. The current accuracy is 25mV , but in the future, there will be a need for higher accuracy.

(B) Reduce the current consumption of the protection IC to achieve over-discharge protection :

As the lithium-ion battery is charged, the battery voltage will gradually decrease over time, and finally fall below the standard value. At this time, it needs to be recharged. If it is not charged and continues to be used, it may not be able to be recharged ( over-discharge state ) . In order to prevent the over-discharge state, the protection IC must detect the battery voltage state. 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 consumption of the protection IC needs to be reduced to the minimum.

(C) Overcurrent / short circuit protection requires low detection voltage and high accuracy :

When a short circuit is caused by unknown reasons and a large current is consumed, the discharge is stopped to ensure safety. In overcurrent detection, the Rds(on) of the Power MOS is used as the inductive impedance to monitor the voltage drop. If the voltage at this time is higher than the overcurrent detection voltage, the discharge is stopped. In order to make the Rds(on) of the Power MOS effectively used in charging and discharging currents, the impedance value must be as low as possible ( currently about 20mΩ ~30mΩ ) . In this way, the overcurrent detection voltage can be lower.

(D) Achieved withstand voltage value :

When the battery pack is connected to the charger, high voltage will be generated instantly . Therefore, the protection IC must have the requirement of " high voltage resistance" (Ricoh 's protection IC can withstand 28V)

(E) Low power consumption :

When protection is reached , the static current consumption must be small (0.1uA)

(F) Zero volt rechargeable :

Some batteries may be stored for too long or for abnormal reasons, causing the voltage to drop to 0V. Therefore, the protection IC needs to be able to charge at 0V.

Future development of protection IC functions

Future development will be as mentioned above, improving the accuracy of voltage detection, reducing the current consumption and packaging of protection ICs , integrating MOS , improving the malfunction prevention function, etc. At the same time, the high voltage resistance of the charger connection terminal is also a development focus.

In terms of packaging , it has gradually shifted from SOT23-6 to SON6. In the future, there will be CSP packages and even COB products to meet the current emphasis on lightness, thinness, and compactness .

Not all functions of the protection IC must be used . A single protection function ( such as only overcharge protection or over-discharge protection function ) can be developed according to different lithium battery materials , which can greatly reduce costs and space , which is not a bad thing for us .

Of course, the goal of functional components being made into a single crystal is a common goal. For example, mobile phone manufacturers are currently moving towards integrating peripheral circuits such as protection ICs , charging circuits, and power management ICs into a single chip, and forming a dual-chip chipset with a logic IC . However, it is currently difficult to reduce the open-circuit impedance of Power MOS and combine it with other ICs . Even if a single chip is made using special technology, the cost may be too high. Therefore, it will take some time to resolve the problem of protection IC being made into a single crystal.