Feasible ESD Protection Solutions for BMS System

The development of cars powered by new energy is getting attention around the world as people care more and more about the environment. Joined by IDTCW, EVTank published the “China’s White Book for the Development of New-energy Vehicles (2021),” which indicates that there were 1.3 million cars powered by new energy running sold in China in 2020 and estimates the sales of 5.3 million new-energy cars by 2025. 

As one of the three cores of a new-energy car as shown in Figure 1, BMS is in charge of the daily safety management of battery banks in order to guarantee the safe and steady operations of the power battery system. That’s why it is very important to the safety of both the driver and passengers. 

Figure 1 The three cores of new-energy car

Principles of BMS

The battery management system, or BMS, detects the status of every single battery in the battery bank to ensure that the entire system is running well, and controls and regulates the battery system based on the status detected, thus realizing the management of charging and discharging of battery system and single batteries for safe and stable operations of the battery system. 　　

Figure 2 shows the electric structure of BMS. The functional modules communicate through CAN bus. With CAN as the connection port between every module, the communication cable can be as short as tens of millimeters or as long as more than ten meters. Due to the complexity of electronics and battery system, interferences caused by ESD and others are frequent as the car is started and running, and these interferences may have impacts on signal cables or power source. The consequences can be as minor as the delay of car’s responses or as severe as interruption or failure of control system and, ultimately, accidents. That’s why the ESD protection is very important to BMS.

 Figure 2 Electric structure of BMS

Feasible ESD protection solutions

Amazing Microelectronic has been dedicated in the development of ESD protection technology and has advanced ESD design technology. For CAN signal protection, Amazing Microelectronic has vehicle-class TVS with AEC-Q101 certification. AZ9424-02S, a commonly used model, features SOT23-3L packaging that protect both CAN_H/L signal cables. For the high-speed CAN FD in the ISO11898-2 published in 2016, we have developed particularly the AZ9427-02S to guarantee its signal integrity at 5M/bps, and the parasitic capacitance is as low as 3.6pF. Also, both TVSs have extremely low ESD clamping voltage, so that the ESD energy is clamped to even lower voltage to prevent internal circuits or ICs from failure due to interference. This clamping voltage is the most important parameter to determine the effects of a protection component on system circuitry. Amazing Microelectronic published a technical article, “Clamping Voltage, the most important parameter for TVS,” on Jul 9 2020 explaining how important the clamping voltage is. Figure 3 below shows the ESD current vs. voltage curves of both models mentioned above measured with professional TLP equipment. With the impact of 8kV (corresponding to TLP current 16A) ESD according to IEC 61000-4-2, TVS keep the clamping voltage at extremely low levels of 31V and 39V.

Figure 3 TLP IV curves

In order to prevent deterioration of signal quality due to interference or energy coupling of master and slave controllers with other electronic components during the process of data acquisition and transmission, the electromagnetic compatibility test, in addition to the basic electric property tests to be met, shall be performed vigorously and the level of testing shall match the actual environment in which the products are used. The national standard GBT 38661-2020 Technical specifications of battery management system for electric vehicles provides electromagnetic compatibility test projects. Car manufacturers may define their own protocols for test voltage based on the performance requirements. For example, a car manufacturer defines the ESD test criterion as 8kV for contact / 16kV in air for Class B, which is 1kV higher than what the standard specifies as a consideration for better product performance and quality. For this, Tier 1 or OEM manufacturers will follow this criterion, or even better. That’s why it is important to select a TVS with excellent specifications. Figure 4 lists some of the test solutions suggested by national standards. 

Figure 4 EMC tests and standards

The electrical transient transmission test is performed according to GB/T 21437.3-2012, where Fast a and Fast b are based on 3a and 3b pulse standards, respectively, of GB/T 21437.2-2008 for a duration of an hour. For this, the AZ9424-02S of Amazing Microelectronic provides not only highly efficient ESD protection but also the ability against specific electrical transient transmission. Figures 5 and 6 provide the ISO 7637 test results of AZ9424-02S performed at a cooperating lab. In DCC (Direct Capacitive Coupling) mode, the product passes Fast Pulse 3a & 3b at ±200V, which is the highest suggested value by GB/T 38661.

Also, there are communication interfaces for control boards and internal sampling modules, including power cables and all sorts of parallel or series interfaces. Amazing Microelectronic has a range of ESD production solutions against the coupling failure due to abnormal energy caused by the voltage fluctuation in the electronic system. Figure 7 shows the corresponding TVS protection components at the power or signal side. All of these products are certified for AEC-Q101. In Amazing Microelectronic, we have cutting-edge semiconductor design technology and we constantly improve and refine parameters to keep the clamping voltage at the best possible level.

Figure 7

Reference: 

 【1】《China’s White Book for the Development of New-energy Vehicles – 2021》; https://max.book118.com/html/2021/0314/6104130154003120.shtm 

 【2】《GBT 38661-2020, Technical specifications of battery management system for electric vehicles》; https://blog.csdn.net/qfmzhu/article/details/105656764