Analytical Expressions of Time-Domain Responses of Protection Circuits to ISO Reverse Transients in Automotive Applications

As the use of semiconductors and electronic control units (ECU) in automobiles has increased, electromagnetic susceptibility has become more essential for the reliability of ECUs. Consequently, automotive ECUs are subjected to electromagnetic compatibility tests to control quality. Test pulses for electromagnetic immunity testing in the automotive industry, such as reverse transients 1 and 3a, defined in the International Organization for Standardization (ISO) 7637-2 standard document, are examined. In practice, it is necessary to analytically investigate the performance of the protection circuits against these reverse pulses. In this paper, theoretical expressions of the time-domain responses of the capacitor filter to these reverse pulses are derived. In addition, the expressions of the avalanche energy as well as the time during avalanche mode are presented. The analytical results, validated by LTspice simulation, show that for the case of pulse 1, the reversal battery-polarity protection device after the filter, i.e., a low-voltage power metal-oxide-semiconductor field-effect transistor (MOSFET), is safe despite entering the avalanche breakdown mode. In the case of pulse 3a, the filter can almost completely remove the transient voltage and hence avoid the avalanche effect of the MOSFET. The verified expressions when the suppressed voltage reaches its maximum are very helpful for hardware design engineers to quickly determine whether the MOSFET undergoes avalanche breakdown.