In the process of designing a car, a major challenge is to protect electronic equipment such as control units, sensors, and infotainment systems from harmful surges, voltage transients, ESD, and noise that appear on the power line. Transient voltage suppressors (TVS) are ideal solutions for protecting automotive electronics. Some parameters are very important for these applications, including power level, off-state voltage, breakdown voltage, and maximum breakdown voltage. The following is the definition of these parameters.
Power level
The power level of TVS is the ability to absorb surge under certain test or application conditions. The industry standard test conditions for the 10 μs / 1000 μs pulse waveform (Bellcore 1089 standard) are shown in Figure 1. This test condition is different from the test condition of TVS transient voltage absorption capability. The absorption capability test uses an 8 μs / 20 μs pulse waveform, as shown in Figure 2.
Figure 1: TVS test waveform (Bellcore 1089) Figure 2: TVS waveform
Breakdown voltage (VBR)
Breakdown voltage is the voltage at which the device enters an avalanche breakdown and is tested under specific current conditions on the data sheet.
Maximum breakdown voltage (VC: clamping voltage)
At a certain peak pulse current level, a clamping voltage will appear on the TVS. The breakdown voltage of TVS is measured at a very low current, such as 1mA or 10mA, which is different from the actual avalanche voltage under application conditions. Therefore, the typical or maximum breakdown voltage marked by the semiconductor manufacturer corresponds to a large current.
Off-state working voltage (VWM): Off-state reverse voltage during operation
The off-state voltage refers to the highest voltage that the TVS can withstand without breakdown, and is an important parameter of the protection device in the circuit that does not work under normal conditions. In automobiles, some automotive electronic product regulations are based on the "jump start protection" situation. In this case, it is required to provide 12 VDC electronic equipment with a 23 VDC power supply for 10 minutes, and use a 36 VDC power supply to power a 24 VDC electronic equipment for 10 minutes without damaging the circuit or causing misoperation. Therefore, off-state voltage is a key parameter of TVS used in automotive electronics.
Initial protection of automobile power cord (load rejection)
Automotive electronic devices such as electronic control units, sensors and infotainment systems are connected to the power cord. The power sources of these electronic products are batteries and generators. The output voltages of these two power sources are unstable, and are susceptible to temperature, working conditions and other conditions. In addition, automotive systems that use electromagnetic coil loads, such as fuel nozzles, valves, motors, electronic and hybrid controllers, introduce ESD, spike noise, and other types of transient and surge voltages into power and signal lines.
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