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Enhancing Battery Performance and Safety with STMicroelectronics L9961 Battery Management System (BMS) Device

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In today’s world, lithium-ion and lithium-polymer batteries have become the power source of choice for a vast range of applications, from cordless power tools to medical devices. However, these batteries are also prone to safety and performance issues, such as overheating, overcharging, and premature aging. To address these issues, STMicroelectronics has developed the L9961 battery-management-system (BMS) device, which provides market-leading accuracy and flexibility to enhance the performance, lifetime, and safety of Li-ion and Li-polymer batteries.

Lithium-ion (Li-ion) and Lithium-polymer (Li-polymer) are both rechargeable battery technologies that have become popular for use in various portable and mobile devices, including smartphones, laptops, and electric vehicles.

Here are some of the key differences between Li-ion and Li-polymer batteries:

  • Construction: Li-ion batteries use a liquid electrolyte, while Li-polymer batteries use a solid polymer electrolyte. The solid electrolyte allows Li-polymer batteries to be thinner and more flexible, making them a better fit for smaller and thinner devices.
  • Energy Density: Li-polymer batteries generally have a slightly higher energy density than Li-ion batteries. This means that Li-polymer batteries can store more energy in the same size and weight than Li-ion batteries, making them a popular choice for thinner devices.
  • Safety: Li-polymer batteries are generally considered safer than Li-ion batteries because they have a lower risk of leakage or explosion. This is partly due to the solid electrolyte and the ability to shape the battery in different forms.
  • Cost: Li-polymer batteries are generally more expensive to manufacture than Li-ion batteries. However, as with any technology, the cost can vary depending on the manufacturer, materials used, and other factors.

One of the key features of the L9961 is its ability to monitor, balance, and protect batteries for diverse applications requiring the high energy density of lithium batteries. Suitable for battery packs up to 25V, the L9961 provides accurate measurements of cell voltages with an accuracy of ±15mV and battery current to within 0.25%, enabling high-accuracy passive cell balancing and coulomb counting. These features support safety measures including overvoltage and undervoltage detection, balance undervoltage protection, overcurrent detection, and short-circuit in-discharge protection.

In addition to its advanced monitoring and protection capabilities, the L9961 also includes a dual pre-driver for controlling battery-pack safety relays, which can be programmed for high-side and low-side connection. The device features an embedded non-volatile memory for configuration data, which relieves the microcontroller from reprogramming the device at each startup. An I2C interface handles configuration and host communication to share battery state-of-charge (SOC) and state-of-health (SOH).

Embedded non-volatile memory (eNVM) is a type of memory technology that is integrated into a microcontroller or other integrated circuit (IC) and is used to store configuration data, firmware, or other critical information that needs to be retained even when the power is turned off.

Non-volatile memory (NVM) is a type of memory that can retain data even when the power is turned off. In contrast, volatile memory, such as random-access memory (RAM), loses its contents when the power is turned off. Non-volatile memory can be implemented using various technologies, including flash memory, EEPROM, and FRAM.

Embedded non-volatile memory is a type of NVM that is specifically designed for use in microcontrollers and other integrated circuits. It is typically implemented using a specialized process technology that allows for the integration of NVM cells into the same chip as the microcontroller or other logic circuits.

eNVM is used in a variety of applications, including firmware storage, boot code, encryption keys, and calibration data. Because eNVM is integrated into the same chip as the microcontroller, it offers several advantages over external memory solutions, including faster access times, lower power consumption, and reduced board space requirements. Additionally, eNVM can be programmed and erased using standard microcontroller programming interfaces, making it easy to use and integrate into a wide range of applications.

Another important feature of the L9961 is its ability to perform pack temperature monitoring with over/under-temperature detection and pack-fuse management when an external thermistor is connected. This feature ensures that the battery remains within safe operating temperatures, preventing the risk of overheating and potential fire hazards. The L9961 is also highly robust to support hot plugging and consumes minimal energy from the battery pack, extending the battery lifetime and increasing safety.

A thermistor is a type of temperature sensor that is made from a material with a high temperature coefficient of resistance. This means that the resistance of the thermistor changes significantly with changes in temperature. Typically, thermistors are made from ceramic or polymer materials that contain metallic oxides or other additives that give them their temperature-sensitive properties.

Thermistors are used in a wide range of applications where temperature sensing is required, such as thermostats, refrigerators, and temperature control systems. They are also commonly used in battery management systems, like the one mentioned in the previous question, to monitor the temperature of the battery pack.

There are two main types of thermistors: negative temperature coefficient (NTC) thermistors and positive temperature coefficient (PTC) thermistors. NTC thermistors have a negative temperature coefficient, meaning that their resistance decreases as the temperature increases. PTC thermistors, on the other hand, have a positive temperature coefficient, meaning that their resistance increases as the temperature increases.

Thermistors are often preferred over other types of temperature sensors, such as thermocouples or resistance temperature detectors (RTDs), because they are small, relatively inexpensive, and have a fast response time. However, they may have lower accuracy and a narrower temperature range than other types of sensors.

Furthermore, the L9961 includes two power-saving modes that cut the current consumption down to 2μA in deep-sleep and 5μA in standby, with the integrated voltage regulator active to resume operation quickly. These features make the L9961 an ideal choice for applications where energy efficiency and performance are crucial.

The STMicroelectronics’ L9961 battery-management-system (BMS) device represents a significant advancement in lithium battery safety and performance. Its advanced monitoring and protection capabilities, coupled with its power-saving features and ability to extend battery life, make it an ideal choice for a vast range of applications. As the demand for safer and more efficient lithium batteries continues to grow, the L9961 is poised to become an industry standard for battery management systems.

Michal Pukala
Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.