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When Bad Things Happen to Good Automotive Electronics Circuits

Safety is critical in automotive design. Cars aren’t cheap, so it’s necessary to protect the investment of the vehicle’s owner. Most important, people’s lives are at stake. That’s why modern automobile manufacturers incorporate various safety features, including airbags, stability control, and tire pressure monitoring. But safety in design goes beyond those obvious protective systems. Safety is a central design consideration for any piece of electronics within the automobile — no matter how large or small.

Whether under the hood or in the cabin, today’s advanced chipsets are highly susceptible to numerous electrical hazards common to the inherently harsh automotive environment. Typical automotive electrical hazards or transients include lightning, electrostatic discharge (ESD), and switching loads in power electronics circuits.

The trouble with load dump
In modern automotive designs, all on-board electronics are connected to the battery and the alternator. The alternator is the main source of electrical transients — the worst of which is load dump. This condition occurs when a discharged battery is disconnected while the alternator is generating current and other loads remain on the alternator circuit. If left alone, the electrical spikes and transients will be transmitted along the power line, leading to malfunctions in individual electronics/sensors or permanent damage to the vehicle’s electronic system. Of course, uncontrolled load dump threatens the safety and reliability of the vehicle.

Automotive load dump protection
Circuit protection devices, including transient voltage suppression (TVS) diodes, and varistors, are the best way to safeguard sensitive electronics against load dump. TVS diodes are silicon avalanche devices selected for their fast response time (low clamping voltage) and low leakage current, but also because they have no inherent wearout factor. Varistors are typically used as the front-line solution for transient surge protection. Examples include ultra small surface-mount multi-layer varistor (MLV) devices for protecting small electronics and traditional mid-range metal oxide varistors (MOVs) for safeguarding small machinery, power sources, and components.

In most modern alternators, the load dump amplitude is suppressed or clamped by adding the limiting TVS diodes at the source of disturbance. Disturbance transients should be suppressed internally or at the terminals of the source by the suppression (TVS diode) devices. As a best-practice, the designer should place the TVS diode as close to the source as possible. The following schematic shows the TVS diode in place and the circuits being protected from load dump.

Additional circuit protection solutions for safeguarding against alternator transients involve the use of AEC-Q200-compliant MOVs. Consider the following examples:

  • An AUMOV varistor can be connected in a Y or Delta configuration with the winding coil of the alternator to clamp the transients.
  • Protect vehicle subsystems (e.g., airbag, powertrain, climate control) from alternator transients with an AUMOV varistor. Use it as a shunt for the transient surge to protect the DC power line against the surge.
  • For protecting against automotive relay surges, use an AUMOV varistor to absorb the arcing energy from the energy released by the magnetic fields of the relay.

Want to learn more about how to protect automotive electronics against damaging electrical transients like load dump? Concerned about improving the overall safety and reliability of automotive electronics through circuit protection and compliance with industry standards? View and download the Focus on Fundamentals Course materials: “Deliver Roadworthy Designs: Safeguard Automotive Electronics With Proper Circuit Protection.”

15 comments on “When Bad Things Happen to Good Automotive Electronics Circuits

  1. Davidled
    December 9, 2014

    Generally, electronic module has an extra protection circuit, i.e. regulator circuit as well. Automotive power architect might better design all power distribution in the vehicle as reducing the total number of TVS and regulator. In some case, I think that there are too many redundant components each other. For example, if vehicle might provide a stable 12 V or 5 V, it is possible that each electronic module might not need to implement its own regulator inside module.

  2. jim_colby
    December 9, 2014

    @DaeJ:  In an ideal world, I would agree that it would be possible to get away from “redundant” protection schemes.  However, it is not always possible to anticipate where the transients will originate, or what they will look like (waveform, energy content, etc.).  So, from a probabilistic standpoint, it is typically better to add protection that may be seen as redundant, but is in place when called upon (transient voltage event).

    Further, it may be possible to “button up” the power distribution to the point that protection components can be eliminated.  However, the treatments to do this would include shielding, uprated components (FETs, sensors, DC/DC converters, etc.) and circuit designs that also increase system costs to the point that the solution is cost prohibitive.

    At the end of the day, protection components (TVS, MOV, MLV, fuse) provide a cost effective “middle ground” in which reasonably priced and readily available power components can be used in a harsh electrical environment and work reliably in concert with equally cost effective protection solutions.

  3. Davidled
    December 9, 2014

    Ideal Vehicle

    Designer might review the analog circuit design with less protected component instead of wire harness. Also, engineer might redesign DTC code related to fuse and any kind of protected device so that service engineer might troubleshoot the vehicle. I am wondering how many protected components are being used in the latest vehicle, compared to that of legacy vehicle in terms of size and location.

  4. jim_colby
    December 9, 2014

    As you would expect, the actual usage of protection devices (fuse, TVS Diode, Metal Oxide Varistor, PTC, ESD suppressors) varies by each model of vehicle and its respective options.  In general, it can be said that as the semiconductor content (ICs, FPGAs, ASICs, etc.) increases, so too does the protection content.  Automobiles, trucks and other vehicles are becoming more “electronic” in nature and so are inherently less robust to voltage transients.

    Circuits like Navigation, Telematics, Advanced Driver Assist Systems and Infotainment did not exist in legacy systems, but are now included, and are typically protected.  In terms of size, what is interesting is that with ESD as a more prevalent issue, we are seeing smaller devices being used for ESD protection on circuits like USB, audio, video, switches, buttons, CAN bus, etc.  Of course, large devices like MOVs and TVS Diodes are still needed on power circuits to protect against switching transients and load dump.

  5. goafrit2
    December 10, 2014

    >>  For example, if vehicle might provide a stable 12 V or 5 V, it is possible that each electronic module might not need to implement its own regulator inside module.

    Automotive circuits are very rugged because they go through quals unlike most consumer markets. They are usually regulated directly or indirectly. The cost model is higher because they are better designed with some redundancies as you noted.

  6. Netcrawl
    December 11, 2014

    @Daej electronic equipments represents a large part of the modern automobile, although electronic modules brings much more comfort and security for the vehicle user, they also bring significant concerns in terms of reliability regarding the automobile environment. several standards have been made to model the electrical hazards that are currently found in automobiles. As a result auto manufacturers have to consider these standards and have to add protection devices to their modules to fulfill the major obligations imposed by those standards.

  7. Victor Lorenzo
    December 14, 2014

    If we take a look at a modern car electronic systems they are mainly built on top of “independet” modules, connected by means of digital and/or optical buses and interfaces. The vast majority of those modules are digital and analog subsystems are limited mainly to sensory. There is a trend to develop and integrate sensors with digital interfaces.

    Even if we integrate a centralized and super-protected DC power module we are in need of distributing power all around the car and that is made using wires and cables. Near 100% EMI/surge inmune cooper cables are not practical for car systems due to cost and volume. It is most cost effective and safe to apply protections at several levels, at leas at interferences source (when practical, like the alternator) and at local modules.

    MOV's and TVS diodes are relatively cheap taking into account the importance of their function.

  8. samicksha
    December 14, 2014

    Yes I agree your point on TVS diodes, but again TVS will fail if they are subjected to voltages beyond those that the particular product was designed to allow.

  9. VarunReddy
    December 14, 2014

    that was exactly what i felt

  10. SunitaT
    December 31, 2014

    @Netcrawl: I see what you are hinting at. Automobiles need the best kind of electronics that are fault proof. Of course, a headlight can be changed, but since automotive industry is trying to go on autopilot and connected car systems, electronics become a major issue. Any fault in the electronics in the ABS braking system or traction control system can wreck havoc. Driverless cars have already been unpopular for one or more reasons, it doesn’t need faulty electronics as the icing on the cake.

  11. SunitaT
    December 31, 2014

    @goafrit2: As you noted, there might be some redundancies in the quality of electronics, and that cannot be helped. I think every shipment of electronics has a defective piece among its ranks, and that may not be deal breaking. If electronics are tested when they are made, and again when they are delivered, the problem goes away since we can easily find the defective piece. Everything cannot beblamed on the electronics supply chain management system.

  12. goafrit2
    January 6, 2015

    >> I think every shipment of electronics has a defective piece among its ranks,

    That is not true if you work in the biomedical sector. The guarantee is that the product not just work in the factory but live in someone's heart for 15 years. If you cannot say SO, you cannot make it.

  13. goafrit2
    January 6, 2015

    >> Driverless cars have already been unpopular for one or more reasons, it doesn't need faulty electronics as the icing on the cake.

    The biggest limitation to driverless cars will not technology. Rather, it will be innovations on roads. You cannot have driverless cars when cities are so broke they cannot patch pot-holes. My doubt on these cars has nothing to do with the technology but on governments that will build the required roads for them

  14. goafrit2
    January 6, 2015

    >>  As a result auto manufacturers have to consider these standards and have to add protection devices to their modules to fulfill the major obligations imposed by those standards.

    And those standards have kept the market to three companies – Conti, TRV and Bosch. It is nearly impossible for a new entrant to get into that sector. No auto company will work with you because of the risk of something working today and in four years blow up for car recall. Yet, that is what the sector needs since cars are designed so that once you know how to drive Honda, you can drive Toyota. Imagine if we have that for software!

  15. nasimson
    January 6, 2015

    @ Sunita:

    > Driverless cars have already been unpopular for one or more
    > reasons, it doesn't need faulty electronics as the icing on the cake.

    Imagine an automobile company like Ford or GM recalling one of their driver-less cars from the market. That kind of scenario will completely shake the customer confidence in their newer models.

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