As we have described in our previous article about automotive overvoltage, automotive electronics are constantly developing new features to improve driving experience. This also challenges circuit protection companies to keep up with the trends and introduce circuit protection solutions that meet the needs of the market. Standard bus systems, LED-based lighting systems, and Advanced Driving Assistance (ADA) systems like park assist or collision avoidance, are becoming more common in new vehicles. Circuit protection is also required for mandatory safety enhancements like TPMS, which are made to increase the reliance on electronics within the automotive industry. In a previous paper, we reviewed the TVS-based overvoltage solution for the most commonly used standard interfaces. This paper is devoted to a study of addressing one of the largest overvoltage events, the so-called load dump.

Electrical transients in automotive electronics

The table shows the different sources of common transients that can impact the performance. Circuit protection standards are important for designers of infotainment subsystems, lighting, drive trains, chassis and safety systems, or body electronics. Circuit protection is important for ensuring safety and reducing warranty costs. The Automotive Electronics Council (AEC), which is responsible for the automotive industry, provides a standard on discrete semiconductor qualifications. This standard ensures that systems are immune to electrical transients. The AEC Q1 01 standard is a set of automotive circuit protection standards.

There are different transients involved, such as:

• Test for electrostatic discharge (ESD) using a human body model or machine.
• Transient generated by inductive switching unclamped.
• The load dump pulse is produced when the generator abruptly disconnects a load.

Three types of voltage transients are possible: ESD (Electrostatic Discharge), Surge, and Load Dump. When a charge exchanges between two objects with different charge potentials, such as between humans and metal objects, electrostatic discharge (ESD) occurs. As a result, a visible spark will be generated. The air discharge voltage is 2-1-5 kV (levels 1 -4) with a relatively low energy and a short duration (ns).

A surge is a transient event of overvoltage that has a longer duration (microseconds) and carries hefty energy. Surge voltages are primarily caused by transients of inductive switching. In car electronics, a load dump is an overvoltage that lasts for a long time, typically milliseconds. This is when a battery is disconnected while being charged by the alternator. Signal levels may reach as high as 174 V and take 400 ms or more to degrade. ISO 16750 Road Vehicles – Environmental Conditions and Testing for Electrical and Electronic Equipment is a standard that automotive electronic system designers should be familiar with. ISO 16750-2 underwent a revision in 2012. ISO 16750-2 is applicable to electronic and electric systems/components in road vehicles. It describes environmental stressors and specifies the tests and requirements for specific mounting locations on/in road vehicles.

ParagraphDescription

Time DurationCauseVoltage AmplitudeEnergy LevelFrequency of Occurrence 

Load dump protection is needed

In paragraph 4.6 of the “Discontinuities” table, there is a section called 4.6.4. Load dumps occur when the generator that is supplying current to a load is abruptly disconnected. This is the case in automotive electronics when a battery is disconnected while being charged by an alternator.

In paragraph 4.6.4, the voltage surge generated by rotating alternators is described.

The transient applied can reach 202 V, and it may take 400 ms for the voltage to drop. The surge current for a 350 ms period can be 50 A if the series resistance is 12 ohms. This is something that the design engineers should consider. In order to pass the repeated test of 1 0 pulses at intervals of 1 minute, any solution for Load Dump Protection must be able to handle the current with resettability as well as without resistance drift.

Switching Solution for Load Dump Protection

In the automotive environment, one of the power supply designs that can be used is LM5088. This controller has protection against load dumps. The solution protects against load dump transients by disabling the input supply for a specified duration and reconnecting with a delay after conditions return to normal. The circuit below is a series disconnect circuit that protects LM5088 from load dump transients.

The circuit is designed utilizing TL431A precision programmable references used for precision series disconnection.

The input range of the LM5088 is up to 75V, which is sufficient for most load dump transients. However, for transients exceeding the upper operating range for the controller, the input supply must be disconnected. Below are other recommended Load Dump Protection Application circuits from Linear Technology or Maxim Integrated.

The cost of manufacturing PCBs and discrete components is quite high.

Shunting Solution for Load Dump Protection

A semiconductor transient suppressor is the most basic way to protect an automotive electronic system.