“Protective MOSFET, protects the battery during abnormal charging/discharging operation”

When loss occurs due to current, temperature rises, so a low on-resistance MOSFET must be used.
Protection MOSFET, parameters required to maintain current balance when used in parallel

[Editor's Note] The market for battery-powered applications such as mobile phones, wireless earphones, and laptops, as well as power tools, service robots, and light electric vehicles (LEVs), is growing rapidly. Accordingly, the importance of the Battery Management System (BMS), an electronic control circuit that monitors and controls the charging and discharging of batteries, is being emphasized. In line with this trend, E4ds has prepared a webinar that introduces the basic components and operations of BMS, and the key considerations for ensuring the performance of MOSFETs used as protection switches, such as low power consumption, excellent thermal interface, avalanche operation, and current sharing between parallel MOSFETs. Ahead of the webinar on May 9, we interviewed Infineon Director Yongjin Kim, who will be the moderator, to learn about BMS and Infineon’s solutions.

▲Kim Yong-jin, Infineon Director

■ Please explain why BMS is essential and how it works.

BMS is an electronic control circuit that monitors and regulates the charging and discharging of batteries. Battery characteristics to be monitored include battery type, voltage, temperature, capacity, state of charge, power consumption, remaining operating time, charge cycles, and other characteristics.

The task of the BMS is to optimally utilize the residual energy present in the battery. The BMS protects the battery from deep discharge and overvoltage caused by extremely high fast charge and discharge currents to prevent battery overload. Additionally, for multi-cell batteries, it also provides cell balancing function to manage different battery cells to have the same charge and discharge requirements.

■ I am curious about the components of BMS and what products Infineon supplies.

The BMS consists of a monitoring IC that monitors the voltage of the battery cells and balances the charge and discharge characteristics of each cell, OptiMOS™ and StrongIRFET™ protective MOSFETs to protect the battery from abnormal operation during charging and discharging, and a PSoC™ microcontroller that checks the status of the battery and transmits this information to the upper system.

In addition, we provide XENSIV™ current sensor and memory that sense the current flowing into the battery, and OPTIGA™ authentication chip that can verify whether the battery is genuine.

■ What should you keep in mind when selecting a protection MOSFET?

The current flowing through the protection MOSFET can range from tens to hundreds of amperes depending on the application. Since current-dependent losses occur and the temperature of the MOSFET increases due to the losses, a MOSFET with as low an on-resistance as possible should be used.

In addition, since protection MOSFETs are mainly used in parallel, MOSFETs with parameters that can properly balance the current flowing through the MOSFETs when used in parallel must be used.

■ Please introduce the special features of Infineon’s protective MOSFETs.

Infineon's protection MOSFETs offer a wide range of VGS(th) values, which are distributed more narrowly than the typical range, and the degree of distribution is managed to be small, which offers various advantages for using MOSFETs in parallel.

Additionally, it offers low on-resistance MOSFETs with a wide safe operating area (SOA). With these unique features, we offer a product with a small package size, which provides the advantage of reducing the system solution size.

■ The batteries used in electric vehicles are typically lithium-ion batteries and iron phosphate batteries. Are there differences in BMS depending on the cathode material?

Lithium-ion batteries and lithium iron phosphate batteries have rated voltages of 3.6 V and 3.2 V, respectively, and their full charge voltages are approximately 4.2 V and 3.6 V.

Therefore, from the BMS perspective, the difference is not great, and it needs to operate accurately regardless of the type of battery used.

■ Please give a brief introduction of the content you will present at the e4ds webinar on May 9th and say a word to e4ds readers.

In this webinar, you will learn about Infineon's BMS solutions and the considerations and countermeasures to take when selecting a product. Through this, you can secure high reliability and long life of the system. We hope you will attend.