Welcome to the ISO 7637 Technical Overview. Why and How to Protect Automotive Circuits from ISO 7637 Threats. When this show is over, you will have the skills, and you will understand the transient standards structure, their goals, their purpose, and how we got here. You'll understand that there are many different agency and corporate standards, but in the end, they all have the same goals.

Most interesting, you'll understand the source of the various test waveforms. And you'll know the questions to ask during product development, and how to find the right TI solutions and support. And you'll be able to recognize opportunities for transient protection and propose alternate transient solutions.

Our agenda. Automotive transient threat environment. This includes L di/dt, inductance sources, and di/dt sources. Then we shall discuss ISO 7637 and related standards. A top-level look with some review of companion and regional specifications, as well as the waveforms and test pulses we all hear so much about.

We'll take a look at the generic solutions that have been out there in the past and are widely used today. Do a little comparative analysis of those solutions, then look at what TI's current solutions are, and some of the roadmap products we have that should be coming out in the future. We'll take a look at the additional support resources, such as TI Designs, Collateral, information, ED forum, things like that.

The things we don't cover. Automotive integrity safety level. We don't cover CISPR, EMI, or any of the EU Directive 72 245 specifications and transit requirements.

Automotive Transient Threat Environment. Circuits, be afraid. V is L di/dt. Be careful, or you'll get kicked.

The threat environment. You can blame inductance most of the time. Why, you ask? Energy release from inductance causes most transients. This is also known as flyback. This is the principle behind many of the power supplies we make, and often it's a good thing. Sometimes not so much. When it's introducing unwanted transients into our systems, that would be the not so much part.

Transient energy is defined as E equals LI squared over 2. So when we look at the transient curves, the area under the curve, E, will equal LI squared over 2. The magnitude of the transient is L di/dt. L can come from a variety of sources. It could be stray inductance, it could be windings in various devices, like solenoids or motors. And the di/dt is typically because a switch is opening or closing.

di/dt can approach infinity since, when a switch opens, the dt is near 0. So when current gets interrupted, we can have a very high di/dt. And even though L might be small, the product of L di/dt can be very high. I blame inductance.

Where are all these transients coming from? We've heard about them. Let's find out their source.

We know voltage flyback spikes occur if current flow through inductance is interrupted. And here, we see a typical system with current coming from a source, the battery on the left over here, and going to a load on the right, or even a couple of loads. But when this switch opens, we'll get a positive spike on the source side of the switch. And we will get a negative spike on the load side of the switch.

And if this is a mechanical switch, then we'll also see arcing transients in there as the switch opens and experiences transients and sparks. Good protection is important. Remember this. One of the key parts of our threat environment is inductance. One of the sources of inductance is inductance in wires.

All wires are inductive. If you want to know how inductive, you can use this formula to determine precisely how inductive the wires are. As a benchmark, an 18-gauge wire is 1 millimeter in diameter, and 1 meter of 18-gauge wire is about 1 and 1/2 microhenries. And since you've got over a kilometer of wire in the average car, that means there's a lot of stray inductance in that car that is a potential storer of energy.

Another source of transient-inducing inductance are motors. And there are motors all over the car. They've got small motors for door locks, for antenna motors. We've got medium size motors to move seats, windows, windshield wipers, and even fans.

And you've got the monster motor, which is the starter motor. And this can draw many hundreds of amps, which really boosts up the I. And it tends to have an awful lot of windings and an awful lot of copper, which creates very large inductance.

A third source of inductance that can produce transients are alternators and generators. These devices have many windings in them with lots of copper and lots of inductance. 10 amps was enough 50 years ago. Simple generator had to power a few headlights and charge a battery. No big deal.

Nowadays, 150-amp alternator is more typical. And up to 230 amps is pretty common for an alternator output. That's a lot of current to be interrupting. And if we talk about eCars and electric cars and hybrids, the currents and voltages there are higher still.

If inductance is the first ingredient to create a transient, then our di/dt, or current interruptions, is the second important ingredient. Where do we get these current interruptions? Switches are a common source. Just turning off a switch while it's conducting, there's a very high di/dt. There are relays.

A switch, generally at higher current, and fuses. When a fuse blows, there tends to be an awful lot of current going through them, and then they open very quickly. And even loose connections have been a source of very high di/dts, especially when that loose connection is on a battery.

To summarize, the threat environment. Inductive flyback is the root cause of ISO 7637 transients. V equals L di/dt. This is important to remember.

And high voltage spikes will occur even with low currents and inductance. There are many inductance sources. We have wire, we have motors, of alternators, and we have solenoids, all contributing inductance to our automotive system. And we have many di/dt sources. Switches, relays, fuses, and even loose connections.