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Components eFuses: Transitioning Faster to Zonal Architectures in Software-Defined Vehicles

From Sreenath Unnikrishnan * | Translated by AI 5 min Reading Time

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Configurable eFuse elements create the conditions for a quicker transition to software-defined vehicle architectures. Why? They not only meet the demands for intelligent power distribution and software-defined zonal ECUs, but also offer cost and space advantages and ensure time-efficient development. Thus, they can present an alternative to traditional fuses.

For software-defined vehicles, many components play an important role, such as eFuses.(Image: Mercedes-Benz AG)
For software-defined vehicles, many components play an important role, such as eFuses.
(Image: Mercedes-Benz AG)

The transition to software-defined vehicles (SDV) is the greatest revolution in the automotive industry in the past ten years. Traditional vehicle designs consisted of hardware-based subsystems that were each assigned specific functions, such as the powertrain or infotainment. However, because vehicle models are developed and modernized in increasingly shorter cycles, it is more efficient to combine several functions into modular, flexible subsystems, or zones. Instead of special area or domain control units, vehicles can now contain two to three zone control units with integrated functions.

The transition to zonal architectures includes replacing traditional fuses with semiconductor switching elements, known as eFuses, which offer numerous advantages compared to fuses. First and foremost, eFuses are resettable, meaning they no longer need to be replaced and can therefore be placed where it is technically most sensible. Because they no longer need to be easily accessible, the wiring connections between the power supply and the consumer can often be shortened. Additionally, eFuses have an improved, significantly less variable current-time characteristic, making it possible to reduce conductor cross-sections and thus the weight and cost of wiring harnesses. The power management system also offers increased possibilities for the prevention and diagnosis of failures, which positively affects power consumption management and makes it possible to maximize the range of electric vehicles. Image 1 illustrates the transition from fuses to eFuses.

Image 1: Replacement of fuses with eFuses in zone control units and distribution boxes(Image: Texas Instruments)
Image 1: Replacement of fuses with eFuses in zone control units and distribution boxes
(Image: Texas Instruments)

Design with eFuses

A connected vehicle must be able to capture the state of the respective system at all times, ranging from demanding sensor functions to protective elements. Last but not least, zonal platforms require flexibility, as the demands on fuses vary depending on the consumer being supplied. eFuses, for example, of the type TPS2HCS10-Q1, can help solve both problems by offering the possibility to configure the switches according to the requirements of the respective consumer via an interface like the Serial Peripheral Interface (SPI). Additionally, they can contribute to informed decisions by reading diagnostic information from the consumer. The overall system costs and component requirements are lower despite the extended range of functions, as eFuses do not require external passive components to configure the protection and diagnostic features.

The constant availability of multiple failure diagnostic features for switches and consumers, realized through the SPI interface, reduces the burden on the microcontroller (MCU). An A/D converter (ADC) integrated into the eFuse element allows for purely digital reading of diagnostic information via SPI, meaning that no ADC in the microcontroller needs to be reserved for receiving current and voltage information. Image 2 illustrates how an eFuse element detects the output voltage and identifies short circuits to the battery as well as a broken connection to the consumer without external components.

Image 2: Sensing output voltage and detecting shorts to the battery and open connections to the load(Image: Texas Instruments)
Image 2: Sensing output voltage and detecting shorts to the battery and open connections to the load
(Image: Texas Instruments)

Among the particular challenges in the transition to SDVs is streamlining software and firmware development to create a cohesive system. If different systems need to be validated for various vehicle models, it negatively impacts time and cost effort. A favorable aspect in this context is that eFuses can be used equally for both low and high load currents and possess a uniform interface for programming and reading information, covering numerous model variants and load currents. The availability of a digital interface for software configuration as well as for control and diagnostic purposes also results in fewer I/O pins being occupied on the MCU, thus reducing costs for additional I/O expanders and the required PCB area.

Why are Software-Configurable eFuses a Good Choice?

Software-configurable eFuses offer several advantages. These include:

  • Configurable current-time profiles: Instead of a uniform limit current, an eFuse element's stored current-time characteristic determines whether and when the shutdown occurs, depending on the magnitude and duration of the load current. Thus, eFuses can allow high current peaks, such as those occurring during the start-up or blocking of a motor, for a short time, but still shut down in the event of a true overload to protect the wiring, circuit traces, and connectors. The SPI-based configurability also allows the fuse characteristic to be programmed with only two parameters, namely the rated current and the response threshold for shutdown, within wide limits. Image 3 shows an exemplary protection scheme for the entire current range.

  • Low quiescent current consumption: Many electronic control units (ECUs) remain switched on even when the vehicle is turned off. Therefore, the eFuses used in the power supply of these ECUs must consume very little current to prevent the battery from discharging prematurely and to keep the necessary consumers active. Despite the lower current consumption, the protection functions remain effective and offer protection against short circuits. More importantly, eFuses can distinguish between active and power-saving modes based on load conditions, allowing them to autonomously perform their tasks without additional effort for the MCU. TI's eFuse portfolio meets all requirements and is characterized by very low quiescent current consumption.

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  • Configurable mode for capacitive loads: Many zonal consumers are capacitive in nature, so the switches used must be suitable for efficiently charging these capacities. In contrast, this capability is absent in traditional fuses and switches. However, eFuses offer a constant current charging mode for cases where significant load currents occur during charging, or a mode with a set peak voltage for consumers with particularly large load capacity, which are charged with a very low current. In both cases, the inrush current is limited to a low value during a programmable period. A beneficial feature of eFuses is that they are suitable for consumers with low or high load capacity by appropriately adjusting the current and voltage limits. Configuring the element for the capacitive charging mode is the best choice to cover capacitance and parallel load current.

Image 3: Programmable features of the eFuse element(Image: Texas Instruments)
Image 3: Programmable features of the eFuse element
(Image: Texas Instruments)

eFuses are replacing traditional semiconductor switches

TI's portfolio of intelligent high-side switches with integrated field-effect transistors and a wide on-resistance range for different load currents helps tackle the challenges in the design of zonal architectures. The eFuse element TPS2HCS10-Q1, with its SPI interface, low-power mode, I2T current limiting, and intelligent capacitor charging function, simplifies development and mitigates technical challenges. With these switches, a more sophisticated power distribution is possible, while providing protection and diagnostic functions.

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*Sreenath Unnikrishnan is Senior Member of the Technical Staff, Power Switches, at Texas Instruments.

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