Explore the Functions and Circuit Configurations of Lithium-ion Battery Protection ICs

1. Types of Lithium-ion Batteries (Lithium-ion Rechargeable Batteries)

Lithium-ion batteries have different make-ups, depending on characteristics such as nominal voltage*, determined by the materials used for the positive and negative electrodes.
The table below describes the typical characteristics of lithium-ion batteries. Furthermore, research and development of materials are constantly improving energy density, cycle durability, etc.
*Nominal voltage: the average voltage of the battery during normal use.

2. Heat Generation, Ignition, and Explosion of Lithium-ion Batteries

Potentially dangerous conditions for lithium-ion batteries are said to occur in the following situations:

Deposition* of metallic lithium due to overcharging

Overcharging leads to the deposition of metallic lithium on the surface of the negative electrode inside the battery. If the deposition becomes dendritic, it can penetrate the separator, leading to an internal short circuit.
*Deposition: A phenomenon in which the electrolyte crystallizes, solidifies, and adheres to the electrode.

Generation of flammable gas due to deterioration of internal electrode material

Overcharging or overdischarging will deteriorate the internal electrode material and cause the generation of flammable gas; it also causes the battery to heat up and expand.

Overcharging and short circuits can cause overheating.

Overcharging or short circuits can cause overheating conditions. This accelerates internal chemical reactions, leading to thermal runaway. Subsequently, the separator may break, resulting in an internal short circuit.

Additionally, symptoms of physical shock and aging can also compromise the safety of the lithium-ion battery.
To safely utilize lithium-ion batteries, multiple risk management components/features are necessary, including protection circuits, charger controls, and flame-retardant materials.

3. Types of Lithium-ion Battery Protection Circuits

Lithium-ion battery protection circuits generally come in two types: (1) a circuit configuration that utilizes specialized ICs for lithium-ion battery protection, (2) a circuit configuration that employs microcontrollers and AFE (Analog Front End) ICs.

The circuit configuration using a lithium-ion battery protection IC is specialized for protection functions in analog operation; and is characterized by low current consumption. As an independent protection circuit, it can also be used as a double protection circuit, in combination with a circuit configuration using a microcontroller and AFE IC.

The circuit configurations using microcontrollers and AFE (Analog Front End) ICs* can offer a range of control functions, however, they tend to complicate development, including software and digital communication verification issues.

*AFE (Analog Front End) IC: an IC capable of monitoring and controlling the status of an external microcontroller by converting analog values, such as cell voltages and overcurrent detection resistor voltages, into digital signals.

4. ABLIC's Lithium-ion Battery Protection ICs

What is a Battery Protection IC?

• A battery protection IC is equipped with overcharge detection/release, overdischarge detection/release, and overcurrent detection functions.
• When protection operation is required, the charge control FET and discharge control FET are turned ON/OFF, automatically controlling the charge and discharge currents.
• Overcharge and overdischarge are detected by monitoring cell voltage.
• Overcurrent is detected by monitoring the voltage across the overcurrent sense resistor, which is inserted into the current path or by monitoring the voltage across the on-resistance used for control.

Related Info.

• Application-specific Circuit Examples of Battery Protection ICs for 1-cell Pack

What is a Voltage Monitoring IC?

• A voltage monitoring IC monitors cell voltage and outputs a signal to the main system when overcharging or overdischarging is detected. Usually, products without overcurrent detection function are named voltage monitoring ICs.
• Voltage monitoring ICs are mainly used for multiple cells. They output a detection signal to the microcontroller when a protection circuit is configured in the main system. If a large number of cells are connected in series and multiple voltage monitoring ICs are required, products with the cascade function are recommended.
• In addition to cell voltage monitoring, there are also products that include the temperature protection function using NTC thermistors and the cell balancing function. Apart from protection ICs, ABLIC also offers products used for simple battery voltage level display.

Related Info

• Battery Protection for UPS (Uninterruptible Power System)
• Battery Protection for e-Bikes / e-Scooters
• Battery Protection for Automotive BMS
• [For Multi-cell Pack] Product Lineup of Voltage Monitoring ICs

What is a Secondary Protection IC?

• A secondary protection IC provides double protection from dangerous overcharging conditions for cells. This IC is completely independent from the main protection circuit and constantly monitors the cell.
• Normally, the charging circuit and main protection circuit control the charging, to ensure that the cell voltage remains below the upper limit. If these circuits fail, the secondary protection IC detects overcharging, causing the protection fuse to blow and cut off the current path; this irreversibly stops charging and discharging. The overcharge detection voltage of the secondary protection IC is set slightly higher than the main charging limit voltage. Therefore, when the main protection circuit operates normally, the charging/discharging path is not interrupted by the secondary protection IC.
• After the protection fuse is blown, it cannot be restored, and the battery pack cannot be charged or discharged. Therefore, during the assembly process of the battery pack, care must be taken to ensure the fuse is opened to prevent accidental disconnection and to avoid the active signal from being output. To reduce the burden during assembly, we also offer a lineup of products that do not require a specific connection order (wake-up function).

Related Info

• Battery Protection for Cordless Power Tools
• Battery Protection for Laptops
• Battery Protection for UPS (Uninterruptible Power System)
• Battery Protection for e-Bikes / e-Scooters
• Battery Protection for Automotive BMS
• [For Multi-cell Pack] Product Lineup of Secondary Protection ICs
• Secondary Protection Circuit Using a Protection Fuse
• Wake-up Function

5. What is Rapid Charging?

Rapid charging is a method that shortens charging time by using a very large current.

The wattage mark on a USB-type charger means that the higher the wattage (W), the faster the charging time, if the devices are compatible.
For rapid charging, it is necessary to precisely control the charge current and be mindful of high-temperature conditions.

In lithium-ion battery protection ICs, the following functions are suitable for rapid charging.

Alarm Function

The alarm function makes it possible to signal the appropriate timing of limit and stop charge currents, extending battery life and improving safety.

Battery Voltage Monitoring Function

The battery voltage monitoring function accurately monitors the voltage of lithium-ion batteries from the charging system side.
This function enables real-time monitoring of the accurate voltage of lithium-ion batteries from the charging system side, improving the efficiency of rapid charging.

Temperature Protection Function

The temperature protection function monitors temperature and controls charging/discharging using an external NTC thermistor.
This function ensures safety by controlling charging/discharging at both high and low temperatures.

6. Discover More about ABLIC's Lithium-ion Battery Protection ICs: Give Them a Try

For details of ABLIC's Lithium-ion Battery Protection ICs, please refer to the following:

Introduction of Battery Protection ICs for 1-cell PackIntroduction of Battery Protection ICs for Multi-cell Pack