Protecting Automotive Power Distribution

It was on a warm summer’s evening aboard a cruise boat on one of Austria’s most beautiful lakes that I was co-hosting an Infineon event to conclude a professional experience week for a group of around 50 students from technical high schools in the region. It was time for the final round for us to showcase our creations.

Smaller groups of around 10 students went from co-host to co-host, and we had just a few minutes to impress with some of our latest innovations.

For my group of students, I rolled out a large black box. I unpacked a plastic casing, around the size of a small suitcase, bearing a DC-DC converter, a printed circuit board with a fuse, two PROFET +2 12V devices, one PROFET Load Guard, and two orange LED lights. This, I explained, was the PROFET Load Guard demonstrator.

PROFET Load Guard demonstrator – overcurrent limitation.

“Watch carefully,” I implored. “I’m going to show you two tricks.” For my first trick, I applied an overload to a load path supplied with a PROFET +2 12V. Predictably, both orange LED lights dimmed down and the DC-DC supplying the application displayed an overload condition. No one looked very impressed.

I continued without further comment. I moved to the second circuit featuring PROFET Load Guard, which at first glance looked just the same. Same procedure, but this time, when the overload was applied, only one LED light dimmed slightly but the other LED light and the power supply were completely unaffected. “And that,” I declaimed, “is the magic of the PROFET Load Guard.” Our students smiled politely, but I could see their curiosity was piqued.

“For my second trick…” I moved back to the circuit supplied with the PROFET +2 12V. “Let’s see what happens when we apply a short circuit.” The students watched carefully as I used the jumper to short circuit the load to ground. Somewhat slower than the students expected, the fuse in the circuitry blew and the application went dark. “What happened?” a student asked. I explained, “Since we can’t apply a real short circuit to this application, which is supplied by the DC-DC converter, the increased current heated up the fuse and forced it to melt. Of course, if it were a real short circuit, the PROFET +2 12V would have reacted faster and protected the circuit. However, the DC-DC was overloaded and the application was at risk because, for a few milliseconds, the fuses’ intrinsic inaccuracy allowed a higher current to pass than the fuse rating. This demonstrably shows why semiconductor devices are superior to fuses.”

I removed the jumper and replaced the fuse. I repeated the short circuit test on the PROFET Load Guard side. Within microseconds, only the affected channel switched off and the application stayed intact. I was met with confused looks.

“How come the application is still running?” asked one student.

“Our PROFET +2 12 V products are equipped with a fixed overcurrent protection threshold, which protects them against overcurrent and overtemperature. But the PROFET Load Guard features an adjustable overcurrent threshold to protect not just itself, but the whole system in which it is embedded, including multiple loads and the power supply. And if there is a short circuit, only the affected load turns off. All remaining loads connected to the PCB are safe. A microcontroller reset gets everything up and running again in no time – a huge advantage over old-school fuses. Being able to adjust the overcurrent threshold means you can isolate a failure from the rest of the application, keeping the current below the system limits. This is why the DC-DC was unaffected when a short circuit was applied to the circuit with the PROFET Load Guard.

“In the previous case, we applied an overload. Again, you could see the advantage of the adjustable overcurrent threshold. The fixed overcurrent threshold in PROFET +2 12V devices protects itself against overload. That’s why, when I applied current that exceeded the threshold, the whole system dimmed down. But in some circumstances, it’s desirable to have a mechanism that protects the whole system.”

“But couldn’t you just use another PROFET +2 12V device?” asked one participant. A good question indeed!

“For the sake of overcurrent protection, you could, yes. But the overcurrent threshold scales proportionally on the R_DS(ON) of the device. Simply put, we chose a device with a similar current capability to the PROFET Load Guard. So these devices are comparable in terms of nominal current. However, PROFET Load Guard’s adjustable overcurrent threshold enables optimized system protection. And if system requirements change, you don’t need to change the device but only the resistor connected to the OCT pin. This in turn allows for design flexibility.”

“And what does this mean for cars of the future?” asked another.

“In simplest terms, this really is cool because it is designed to future-proof dependable power distribution. It means you can run multiple kinds of loads requiring different levels of current. With the integrated capacitive load-switching mode, we can also address the increasing numbers of capacitive loads, which means you can quickly switch them on within the safe operating area. Ultimately, all features of PROFET Load Guard aim to protect the load supply and the power distribution system. This is why we call these devices PROFET Load Guard!”

Our conversation moved from theory to practical applications.  “You can use it in automotive power distribution and modern zone architectures for sensitive or capacitive loads, which require nominal currents up to 3 A. These could be Power over Coax (PoC) for camera modules, display modules, or zone modules. Even today, the demands on power supply are many and varied and system failure is not an option. The PROFET Load Guard solution keeps things lightweight, simple, and safe.”

Student engineers see first-hand how Infineon’s PROFET Load Guard protects an automotive power distribution, Faaker See, Villach.

It was something of a light-bulb moment! Our attention returned to the box.

“So the demonstrator box is essentially a bit of kit for trainers and sales guys, right?”

“Yes, the demonstrator helps us to explain the optimization potential of choosing PROFET Load Guard.”

“Is there a way that students like us can get our hands on a demonstrator? I’d like to try it out!”

“Well, I don’t have enough fuses to let you all try it out but the great thing is – you don’t need a ‘physical’ demonstrator.  You can just use its online digital twin! If you like what you’ve seen and have a practical application in mind, you can download the simulation model. Just try it out with your own application requirements. The PROFET Guard tool can help you with your design by calculating the required external components according to the current limitation. Not only is it user-friendly – it’s license-free and free-of-charge too.

“Designers in manufacturing environments can order the evaluation board and try it out in the lab together with our Infineon Smart Power Switches Configuration Wizard. All the available online material aims to simplify the design-in process”.

Enough said. It was already time for my next group of students. At the end of a magical day, my greatest trick might have been to share a glimpse of the future of power distribution with our engineers of the future.