Designing the Safe EV of the Future

Once powered systems in vehicles migrated beyond simply starting and operating the motor and peripheral systems, automotive electronic content’s ubiquitous and expanding nature now dominates the industry. Even the most advanced fueled vehicles require a significant percentage of their value to be in their electronics, for operation, navigation, and sophistication (Fig. 1).

Figure 1: A car's electronic content’s ubiquitous and expanding nature now dominates the industry

To take a closer look at the state of automotive system design, we spoke with Tamer Kira, Executive Director, Business Management at Maxim Integrated, about the challenges in designing the safe electric vehicle of the future. The company has been very active in the development of vehicular subsystems employing the latest chipscale advances.

Recently, the company released the MAX17852, a 14-channel, high-voltage, ASIL-D data-acquisition system to address these complex management issues. Designed for integration within electric vehicles, hybrid electric vehicles, and other transportation systems, the IC addresses smart junction box, 48 V, and other automotive battery systems which can see voltages up to 400 V and beyond.

EE: It's really exciting to be in the automotive industry today, this market has really been taking off over the past few years.

Tamer Kira: You look at what's happening in terms of growth between 2017 and 2023, it's a 28% CAGR and really what does that mean? I mean it's growing every single year basically by leaps and bounds. OEMs are investing billions of dollars into this. One article I read said that one third of all new cars in the next two years are going to be electric, right? You're entering into an era where there's not only interest already from the consumer, but the OEMs are actually also going to be offering a lot more cars that the consumer can buy.

On top of that, you also have governments who are beginning to say, "Okay, hard deadlines by a certain date." You have California saying, "By 2035, only electric vehicles can be sold." China saying, "By 2035, 50% of their cars have to be electric. In various countries they have also come out with different mandates. So there's a lot of push and a lot of effort going to this to make this 28% CAGR happen. In my guess, I think it's actually going to continue to increase. That CAGR is actually going to go up even more. There's one study that says by 2025, 25% of the cars in Europe are going to be electrified.

Tamer Kira

EE: Well, we haven't even reached the true tipping point yet. So things can only scale upwards.

Tamer Kira: Yeah. In the past, let's say five years, the biggest market in the world was China and it was growing every year by at least, for the most part, high single digits or double digits. This year, they were actually surpassed by Europe or I should say, sorry, 2020, last year, they were surpassed by Europe. So Europe actually this last year sold more electric vehicles and plug-in hybrids than China did. It grew at over a 100% year over a year. Now Europe is becoming the largest market in the world for it. And you talk about their percent sales, their percent sales, they're about 7% of their car sales now are electrified. In terms of the whole world, I agree with you. I don't think we've hit that tipping point yet, but Europe, it's getting close to that point.

EE: It's close to it.

Tamer Kira: Yeah.

EE: You see more Teslas in Germany on the streets, more and more every day, but then again the form factors work for Europe. You know what I mean? Small, mid-size cars are the market leaders here. In small urban areas, which is the sweet spot for EVs.

Tamer Kira: Yeah, so it's an interesting point because we're not really going to talk about it too much today, but chargers is the infrastructure. That's really a big deal, and really in terms of enabling electrification you have a lot of money being poured into the chargers and the network system for electrification. I mean, just here in, in the US, Tesla has over a thousand superchargers between the other companies that are also offering superchargers. But so, I mean, there's a lot of money just going into that to enable the different cars to really have that support.

When we talk about electrification, what does that mean? You look at your car, there's a lot of different components to the car, right? What we're going to focus on today is the battery management. You have a big battery pack, right? You have the battery management systems that really support that battery pack. In Europe, actually, I think by 2025, there's an expectation that all the OEMs are going to switch over from lead-acid, 12-V batteries to lithium-ion batteries. That's one form. It's small, but it has an impact on CO₂. Then you really start stepping up into really the world where you can make a big difference in terms of CO₂ emissions.

You get your battery electric vehicles, which are 400-, 800-V systems, 50 kW, 100 kW, and a few out there are pushing even higher than 100 kW now, but really the big focus there is to get the range for the consumer and the efficiency. The other big piece that you're seeing in this market is the E-Trucks and E-Buses. In terms of the buses, you could have 750-V-plus battery-pack systems. You have some governments that have already also said going forward, they only want electric buses in their infrastructure and their systems. And for those, you're talking about a 120- to 240-kW-hour battery pack. You're really stepping it up.

Figure 3: A basic block diagram of a power system

Tamer Kira: When we talk about battery-management systems, what does that really mean? What does that really do? This is just a basic block diagram of what you see in a system. Here (Fig. 3) you'll see the battery modules and it really depends on the OEM. It depends on the type of battery they use. You could have a few hundred batteries to 7-8,000 batteries in a car, but really across the board, what's important is that all these different points we're monitoring them, right? You're monitoring the cell voltage for each battery. You're monitoring if there's a busbar measurement. You're monitoring module voltage. And then in all of that, you're comparing the pack voltage for the module voltage to the cell voltage in terms of your safety analysis, so that's what these battery supervisor ICs do.

Now in between your battery pack and your motor, that's actually driving your car, you have these big relays contactors and there you're also monitoring the contactor voltages. You're monitoring contactor voltages here. You're monitoring the pack current, and so that is inside your junction box, right?  One of the concerns OEMs have is they want high safety, you need to be able to measure all of these safely and quickly. Now, as we talk about what the challenges are for the OEMs, high safety requirements. 

The highest level, there's four levels, there's ASIL A, B, C, and D. They all want ASIL-D now. That's really a big requirement. They want to be able to measure it for all those contact points that we talked about. Voltage current, and temperature. You also have different temperature points that you're measuring. Other things that they want is communication.

One thing we didn't really talk about is in each car, you could have, seven, eight, 10, 15 different ICs that are measuring the voltage and the current and temperature, and it's important that they all talk to each other in a fast, reliable architecture. The big deal with the batteries is they all have to be close to each other's battery voltage, as much as possible. You can't be off by a volt between batteries. They need to be like down to millivolts, depending on OEM requirements. So that communication needs to be fast, and it needs to be reliable. You need to have a really robust BCI, bulk current injection testing on it, and immunity.

Now, with all of this, I mentioned how many ICs there are per car. You could have, eight, 10, 15 ICs for car. Having that small footprint really helps, right? Because when you're putting so much circuitry out there, you want to be as compact as possible so high integration is a big deal. Again, when you're multiplying by eight, 10, 15 ICs, and all the components in out, and BOM becomes a big deal. You're spending quite a bit of money on these electronics, and you need for it to be optimized.

Now, we also talked about all these different points that we're measuring, voltage, current temperature, they all have to be accurate. They have to be accurate. They have to be fast. They have to be time aligned. And then all of that needs to be scalable. We talked about all the different architectures out there. You need a system that will scale from the smallest little smart car, if you will, to the biggest massive, Hummer or bus that you see out there.

The question is, okay, well, how do we answer that? So we have the MAX17852 today. It's the first ASIL-D data-acquisition product of its kind on the market, an acquisition system that does voltage, current, temperature, and communication. Right. And this is important.

EE: Is timing centric to the device, or are you going with the bus timing?

Tamer Kira: It's centric to the time alignment to all those different components we talked about. We talked about voltage, temperature, and current, all of those need to be aligned. That way when they do a calculation, it's actually at that instantaneous point in time, and they can calculate basically the power requirements, what's being delivered, and what's required, and if there are any concerns with heat, or if there are any concerns with system performance. Having that tight time alignment really, we've heard some OEMs really focus on that as a key requirement for the architecture.

When you look at the 17852, if you look at the internals a little bit, I just kind of want to dive into some of the aspects that really help what we talked about measuring the voltage, the current, temperature, and the ASIL, the high safety. First of all, one thing that's different is that we have an integrated current sense amplifier, it gives you the flexibility. You can use a shunt resistor to measure your current, which many OEMs do today. Or you can even use a hall sensor and use one of the auxiliary inputs for that. It really gives you that ultimate flexibility.

For the temperature, you have the inputs for sensors that will go in straight to the ADC.That gives it a fast, reliable measurement. We must have comprehensive diagnostics. Really the big deal, probably the biggest deal here, is the fact that you have to be ASIL-D across the board for all of this stuff. Having a highest level of diagnostics, and that means checking the IC path internally. That means checking also the batteries in terms of leakage, in terms of opens, in terms of shorts, or if something's going on with that battery you need to know. That's part of what a really solid battery management system will look like. This is the secret sauce, if you will.

Another big deal is really having two non-homogeneous measurement engines. It's a state-of-the-art SAR ADC, right? This really gives you that fast, accurate time-aligned measurement that we need. We also have a second measurement engine. It's important that these two are different, and not the same because if you have some type of failure...

EE: They aren't prone to the same error.

Tamer Kira: Exactly. When you're looking at the two different measurements, you will see that there are two different. If there's something wrong, you'll at least still get one good one, and you get one bad one versus if you have something that is prone to the same error, then you may not know about it until later. You've probably heard a few stories about that. And then the other last piece here is having the flexibility to do capacitive or transformer isolation. We talked about having the smallest boards possible, capacitive isolation's a big deal, but it also helps with BOM costs.

But there are some OEMs who still want to do some type of transformer isolation in between those, all those ICs that we talked about earlier. Having that flexibility really gives them the ability to do what they want. In summary, what we're talking about here is having this 14-channel highest ASIL safety, ASIL-D compliance for all major components of the battery.

EE: A higher level of awareness.

Tamer Kira: Yes. It's a higher level of awareness, and  it also enables them to optimize their system for their charging or discharging in terms of the power management, because now by being truly time-aligned between current and voltage and temperature. I'll give you a use case, they want to keep their temperature below 85 degrees. They're basically pumping current in, and as they're charging or discharging, as they're measuring the current and the temperature, "Okay. Now we're getting 84, 85 degrees. Let's change the current so we're under that temperature profile." It's time-aligned within tens of microseconds. We've gotten a lot of feedback on that it gives them, the OEM, the ability to really manage how much power they're pushing through the system.

Also, with this you can get up to 16% space savings, up to 20% cost savings if you compare it to a discreet junction box. In a junction box where you have the big contactors, there's different ways of doing that. You could do it with a discrete solution, you can do with other different ways, and if you compare us to a discrete solution, you're talking about some significant savings, 16% space and 20% cost savings.

Then there are also other halo-effect advantages like time alignment, you get the measurement accuracy, best current-sense amplifier gain for the time-align measurement. Our current-sense amplifier gives you a good solid measurements at 0.3%. You can use this basically across the board into the different applications between the electric hybrid, plug-in hybrid, or any other transportation. The other big thing out there that I didn't mean to really talk about is E-Bikes and E-Scooters, actually it's also very ideal. We've gotten a lot of traction was the E-Bikes and E-Scooters because they want a one-size fix-it-all for their systems. 

The one thing I'll finish on is really just emphasize the whole time-alignment concept. So in one daisy chain, you get the cell voltage, the busbar, the module voltage, a pack voltage, a pack current, contactor voltages, temperature, all of that, highest ASIL level, ASIL-D, time align was in tens of microseconds, right? Our picture is really system enablement to enable that whole system in one fell swoop.