A major challenge in automotive design is protecting electronics, such as control units, sensors, and entertainment systems, against damaging surges, voltage transients, ESD, and noise that are present on the power line.
Automotive electronics, such as electronic control units, sensors, and entertainment systems, are connected to one power line. The power sources for these electronics are the battery and alternator, both of which have unstable output voltages that are subject to temperature, operating status, and other conditions. Additionally, ESD, spike noise, and several kinds of transient and surge voltages are introduced into the power and signal line from automotive systems that use solenoid loads, such as fuel injection, valve, motor, electrical, and hydrolytic controllers.
Transient voltage suppressors (TVS) are well suited for automotive electronic protection and have several important parameters for these applications, including power rating, breakdown voltage, maximum breakdown voltage, and stand-off voltage. Following are definitions for these parameters.
The power rating of a TVS is its surge-absorbing capability under specific test (Bellcore spec) or application conditions.
Breakdown voltage (VBR)
The breakdown voltage is the voltage at which the device goes into avalanche breakdown, and is measured at a specified current on the datasheet.
Maximum breakdown voltage (VC: Clamping voltage)
The clamping voltage appears across the TVS at the specified peak pulse current rating. The breakdown voltage of a TVS is measured at a very low current, such as 1 mA or 10 mA, which is different from the actual avalanche voltage in application conditions. Thus, semiconductor manufactures specify the typical or maximum breakdown voltage in large current.
Stand-off voltage (VWM): Working stand-off reverse voltage
The stand-off voltage indicates the maximum voltage of the TVS when not in breakdown, and is an important parameter of protection devices in circuits that do not operate under normal conditions. In automotive applications, some regulation of the automotive electronics is provided by “jump-start protection.” This condition supplies 24 VDC in 10 minutes to 12V type electronics, and 36 VDC in 10 minutes to 24V type electronics without damage or malfunction of the circuit. Thus, the stand-off voltage is one of the key parameters in TVS for automotive electronics.
Learn how these TVS parameters come into play for protecting circuits during a load dump by reading the complete tutorial feature here, courtesy of Automotive Designline Europe.