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Technical Article

How to Maximize Powertrain Efficiency and Reliability
with High-accuracy Temperature Sensors

Bryan Padilla
If you design automotive systems, you may feel tremendous pressure to redefine vehicle powertrain systems tomeet the reduced greenhouse gas (GHG) emissions goals established by initiatives in the European Union,
United States, China and Japan, just to name a few. To meet these targets, some automobile manufacturers
are implementing 48-V systems for mild hybrid electric vehicles, but most are transitioning traditional internal
combustion engine (ICE) models to an all-electric powertrain system, as shown in Figure 1.
Due to environmental goals for emission reduction, electric vehicles (EVs) are projected to quickly increase theirmarket share over the next decade. To help speed the adoption of EVs, powertrain suppliers are designing
integrated electric powertrains that include the traction inverter, DC/DC converter and onboard charger in onebox. While this approach reduces vehicle weight, lowers overall costs and provides higher power density, it
requires greater focus on thermal management. This is because higher power densities and smaller form factors
increase operating temperature, which can degrade powertrain system performance – or even worse, damage it.
Temperature sensors have always been a necessary component within vehicle powertrains, but because they’reoften a second thought or reused across designs for years, their positive impact on electric powertrain systems
has been limited. New temperature sensor technology with proper implementation can have a great impact on
the efficiency and reliability of integrated electric powertrain systems.

Figure 1. Electric Powertrain Systems
Better Temperature Accuracy Can Help Increase the Efficiency of Integrated Electric Powertrains
Consumers want EVs to charge more quickly and to have more driving range on a single charge. In orderto achieve this, designers must increase the efficiency of the integrated electric powertrain. One approach isto increase the voltage levels and switching frequencies within the power stages. However, doing so in sucha small footprint intensifies the power density and causes temperatures to rise, adding to the risk of thermalrunaway. Achieving this increase in efficiency while limiting the risk of thermal damage requires the proper use ofaccurate temperature sensors and active cooling feedback loops.
Safely pushing components to their peak performance typically results in higher operating temperatures closer
to device limits. As shown in Figure 2, maximizing sensor accuracy enables the processor to minimize thetemperature safety margin of error so that it can more precisely control functions such as vehicle charging andpower flow – even when close to the thermal operating limits of your devices.
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Figure 2. How Accuracy Affects Safety Margins
Low-drift Temperature Sensors Help Maintain the Reliability of Integrated Powertrain Systems over Time
Consumers want their vehicles to last. The lifetime of the electronics found in an integrated electric powertrain
directly correlates to the temperatures at which they were exposed. In order to keep components such as thepower-stage field-effect transistors operating correctly for many years, temperature sensors must be reliable andhave minimal drift.
Many electronics drift over time, and temperature sensors are no exception. Drift has a lot to do with asensor’s material composition. For example, silicon-based temperature sensors have negligible sensor drift
over time, while resistance temperature detectors drift anywhere from ±0.1 to ±0.5°C per year, and traditional
negative temperature coefficient (NTC) thermistors typically drift >5% over time (not including the drift of externalcomponents). As your system ages, sensor drift can increase the error of your temperature sensing solution andlimit its efficiency by forcing it to shut down prematurely or cause thermal damage to components.
When designing for long-term performance, it’s best to use a temperature sensor integrated circuit (IC) thatprovides guaranteed accuracy over its full operating temperature range, as opposed to the questionableaccuracy that discrete implementations such as NTC thermistors have when uncalibrated. A digital temperature
sensor such as the TMP126-Q1 enables precise monitoring up to extremes as high as 175°C with ±1°Caccuracy, and down to ±0.3°C across a wide temperature range. In the case of voltage transients and surges
within the system, temperatures can increase pretty quickly.
As Figure 3 illustrates, the TMP126-Q1 helps your system take preemptive action by detecting temperature
spikes, which may be a leading indicator of thermal issues before the temperature reaches dangerous levels.

Figure 3. The New Slew-rate Alert Feature in the TMP126

2How to Maximize Powertrain Efficiency and Reliability with High-accuracy
Temperature Sensors
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As I mentioned previously, you might want to increase switching frequencies to boost efficiency, but that may
lead to unwanted electromagnetic interference (EMI). To operate in high EMI conditions, the TMP126-Q1 has abuilt-in cyclic redundancy check to ensure the use of data only when it is error-free. Additionally, the TMP126-Q1
comes with functional safety failure-in-time (FIT) rate and failure mode distribution (FMD) documentation to helpachieve system-level certification. The device’s high accuracy and negligible drift enable integrated powertrains
to reduce their protection margins, shutting down less often while still protecting the system from overheating,leading to greater efficiency.
Conclusion
It’s not surprising that you can find over 20 temperature sensors spread across integrated electric powertrainsystems. Accurate sensing can help maximize your system’s efficiency, prevent false triggering of control
systems, and protect ICs or other components more effectively. Being able to maintain that efficiency over time
to keep automobiles on the road longer is possible with low-drift sensors made out of silicon. No matter what
temperature sensor you choose, remember to choose an accurate and reliable one, follow sensor placement
best practices, and leverage new sensor features.

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Temperature Sensors
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