Automotive demands driving passive components to extreme performance

The increased sophistication and performance expectation of the automotive drive train, especially in electric vehicles (EVs) and to a lesser extent in hybrid and even internal combustion engine (ICE) vehicles, is accelerating the usual push/pull improvement effect between advanced components and their end products.

I recently saw a press release from Texas Instruments for the RES80A-Q1, a 50-MΩ precision-resistive divider for use at extremely high voltages up to 2,000 V DC (Figure 1). These simple matched-resistor dividers are used to ratiometrically divide a high voltage down to a much lower voltage, so it can be measured with conventional electronic circuitry to give the vehicle battery management system (BMS) the data it requires.

My initial thought was that this part must be targeted toward the traditional uses of these components such as X-ray machines or high-voltage physics projects and their electric fields. But then I saw the part was qualified to AEC-Q200—the automotive-grade rating for passive components—and the primary use for this resistive divider is in high-voltage EV battery packs.

Figure 1 The RES80A-Q1 50-MΩ resistive divider has two precisely ratioed resistors in series with a center tap. It’s used for dividing an input voltage down to a more-manageable value (below). Source: Texas Instruments

While it’s conceptually a simple component, its actual fabrication is sophisticated, and its specifications are very tight. It’s built on high-performance analog-wafer process with an insulative silicon dioxide (SiO₂) layer that encapsulates the resistors and enables sustained use at up to 2,000 V DC. The tiny 8-pin SOIC package has a nominal body size 7.5 mm × 5.85 mm; but it also features creepage and clearance distances of at least 8.5 mm between its high-voltage and low-voltage pins, as required by various safety mandates.

It features high ratio-matching precision, with the measured ratio of each divider within ±0.1% (maximum) of the nominal. Figure 2 shows the standard high-voltage to low-voltage (R_HV:R_LV) ratios offered.

Figure 2 The AEC-200 qualified passive component is available with different pre-set ratios to match the specifics of voltage division of the source. Source: Texas Instruments

This precision is maintained over the specified temperature range and aging with a cumulative drift of only ±0.2% (max). Therefore, the lifetime tolerance of an uncalibrated RES80A-Q1 remains within a ±0.3% (max) envelope.

In short, the performance of this apparently simple ratiometric device is impressive, and beyond what I thought a mass-market application such as automotive-voltage measurement would require. As a standard catalog item, it’s available to automobile subsystem OEMs, but also to the broader market.

We’ve seen this spillover scenario many times, especially with technology advances that occur as component vendors introduce new products which are useful to other, unrelated applications. As standard catalog parts, they can be “picked up” by non-automotive designs to simplify their sourcing challenges while avoiding the need for a low-volume part that may need to be custom fabricated and evaluated at considerable cost in time and money.

But what about the automotive end user?

While the off-the-shelf availability of specialized components such as this resistive divider is a good thing, there’s also downside to the increased sophistication of cars that does concern me. On one side, modern feature-laden cars are generally more reliable than cars of a few decades ago. According to the Kelly Blue Book, the average U.S. car is now over 12 years old. Though I am usually skeptical of such statistics as they are often based on extrapolations and “guesstimates”, the data on cars is very robust and accurate.

Industry “watchers” attribute this longevity to two factors. First, cars are better built and generally more reliable. Second, new cars are so expensive that in many cases, it pays to keep fixing them for more years.

However, their increased complexity and enhancement features, and the advanced components and circuitry these require, make it much harder to diagnose problems and more costly to fix them. Now, many replacement parts are highly specific to a specific vehicle’s make, model, and year.

It wasn’t always this way. Decades ago, an auto vendor used many parts in common across individual models; sometimes they were common even across brands (think fuses). For example, the car headlights were limited by regulations to just a few sizes and types; you could get a replacement at any auto-supply store and replace it in a few minutes. Now they are integrated into the car body and are unique to each make, model, and year, but do offer improved illumination along with greatly reduced drag (Figure 3).

Figure 3 Those were the days: Until the later 1900s, automobile headlights were standardized with just a few available sizes and form factors. Things have changed now, as the headlight assembly is an integral, structural part of the car. Sources: Pinterest and Etsy

Today’s repair-related supply chain is more extended and fragile: my low-mileage 2019 car was off the road for two months while I waited for a replacement electronic door-lock module. There were also hard-to-find issues related to module vampire/parasitic drain, killing the battery.

In the case of these high-performance passive components for cars, do their performance benefits outweigh the long-term owner-centric challenges they also bring? That’s an unresolved question and is different for different car owners and their specific circumstances.

Have you ever used a specialized passive AEC-Q200 part in a non-automotive design? Why did you choose that route? Was the choice worthwhile in the end, or did unexpected surprises with respect to performance, availability, cost, or support make you reconsider that decision?

Bill Schweber is a degreed senior EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features. Prior to becoming an author and editor, he spent his entire hands-on career on the analog side by working on power supplies, sensors, signal conditioning, and wired and wireless communication links. His work experience includes many years at Analog Devices in applications and marketing.

Automotive demands driving passive components to extreme performance

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