Modular EV-Power Subsystem

2024. 1. 30
Charging an electric car
Futureproof EV Power

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Challenge
  • EV makers must support a growing range of loads and power density while supporting a robust roadmap in highly cost-sensitive markets.

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Solution
  • A modular power subsystem with a high degree of flexibility to meet application needs while maintaining a heavy leverage/reuse model and cost competitiveness.

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Application
  • Effective monitoring, control, and communication for diverse load support in EVs.
  • Multiple ECUs govern sensor management, data, interface, communications, and safety.
  • Controller Area Network (CAN) bus requires galvanically isolated power.
  • Consolidate downstream rails onto larger power converter to reduce size, cost, and improve efficiency.
  • Incorporate latest power solutions in EV roadmap for economic opportunities and adaptability.

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Teaser

Electric vehicle (EV) makers have to accommodate an ever-growing list of sensors, devices, compute units, displays, radios, motor drives, and other loads, which can have a wide variety of power support requirements. Besides multiple voltage rails, these needs span from isolated vs. non-isolated, regulated vs. unregulated outputs, and support for a wide input voltage range. High efficiency is also critical in a space where every milliwatt dissipated translates directly to the EV’s range (e.g., “fuel” life) and, consequently, the value proposed to the end user.

Adding to the challenge, these EV makers (and the Tier-1 organizations supporting them) must deliver solutions to adhere to rigorous and robust quality and reliability standards (e.g., AEC-Q100 certification) and withstand harsh environments with wide temperature swings, all while adhering to stringent cost considerations. In addition, they must meet all the specifications with a design flow that is highly amenable to leverage and reuse models, ensuring a predictable and futureproof product development roadmap.

Story

The EV’s Power Design Manager (PDM) must propose power subsystem solutions to support isolated CAN buses, several lower-power sensor/compute loads, and isolated gate drives for motor drives big (kWs) and small (10s of Ws). The new regulatory requirements being enacted in all major markets worldwide are trying to mitigate combustion driven vehicles for the sake of sustainability. For the PDM, this means putting extra effort into sharpening their pencil for a strategy to develop a fast-evolving and cost driven product development roadmap. In terms of power solutions, this translates to prefabricated power subsystem blocks that can be standardized and commoditized but still easily semi-customizable for slight changes to load voltage/ power levels. This thought process also applies to the input voltage side since the primary vehicle voltage bus would be derived from the EV’s battery pack, which may tend to increase over time, though not always in a predictable manner.

Just when the PDM thought they had viable solutions to propose, the Product Line Manager informed that any proposed solutions must be highly leverageable or reusable since development timelines are short, with the next model immediately around the corner. Furthermore, the PDM must carefully consider all these factors when proposing a long-term roadmap that is not forgiving of changes in main voltage levels on both input and output sides of the power converters (i.e., support for different battery pack configurations, different motor drives, and increasing power demand for most loads over time). And, of course, they also reminded the PDM of their top three priorities: cost, cost, and cost!
The readily available evaluation verification module (EVM) boards and reference designs for all RECOM solutions are being considered to get a component quickly and easily onto a designer’s bench for analysis and verification of the proposed power solution without having to worry about laying out the design and being reluctant of the impact of external components/factors. This way, designers can stay focused on vetting their applications with confidence by leveraging a well-designed and pre-qualified, commercial off-the-shelf (COTS) power solution. Recognizing the frequent use of CAN bus in the industry, RECOM partnered with a top-tier semiconductor supplier on a CAN-bus, isolated power reference board, that combined RECOM’s R1SX-3.305/H with their CAN transceiver.

Given the need for multiple CAN buses to support a vehicle, the PDM understands the importance of having multiple solutions to choose from based on the available space and budget for each. RECOM provides some tailor-made options for CAN-bus applications. The R05CTE05S is proposed as the primary workhorse due to its cost-effective and low profile package. Though many of the EV’s control boards are in tight spaces, the 2.5mm high, 16-pin SOIC package provides the CAN bus transceiver with a driver that will not increase the overall height of the subassembly. Additionally, since one of the PDM’s designers needed to source the CAN bus supply from a shared 3.3V input with a CPU, the R1SX-3.305/H was proposed, which was a solution already qualified by the designer on the top-tier semiconductor supplier’s EVM. Since RECOM was aware of the need for flexibility and growth potential, they also informed the PDM of the R1DX series, in case they required a dual-output (+/- Vout), isolated solution (i.e., +/- 10V analog sensors).

Considering that output isolation requirements can vary across loads, the PDM is looking for upstream, non-isolated solutions that offer various power levels, package sizes, efficiency/thermal envelopes, and price points. Though the 12V main bus is currently the most common in the fleet, it is well-documented on the company roadmap and throughout the EV industry that main bus voltage levels will be pushed higher (24+ V) to accommodate advanced power distribution schemes. This change aims to either deliver more power with less current and/or account for the voltage drop of longer wiring routes, given how much wiring is in a vehicle and how that directly translates to weight and, therefore, range. The PDM also recognizes that system power budgets and load requirements only tend to increase over time, even as power converters become denser and more efficient.
To address these needs, RECOM engineers designed several solutions optimized for non-isolated applications with wide and migrating input voltage ranges. These solutions prioritized high efficiency and included the standard protections (SCP, OCP, OTP, UVLO) in space- and cost optimized options, especially for automotive and industrial applications. In this lower power space, the RPMB5.0-3.0 provides 15W of power in a drop-in, EMI-shielded, 25-pad LGA module. For the subassemblies of smaller processors, sensors, and interfaces only requiring <10W of regulated non-isolated power, the RPX-1.5Q can accept up to 36Vin and still provide 7.5W of regulated power in a compact 3 x 5 x 1.6mm thermally enhanced QFN module. Regardless of the upstream selection, the PDM finds it is more cost effective and space-efficient to add the lower-power downstream converters tailored to the needs of isolated power rails only when required.

Saving one of the biggest challenges for last, the PDM faces the task of supporting a wide variety of requests for isolated gate drivers to drive the many flavors of power switches used throughout the vehicle. Motor driver (i.e., common inverter) circuits are used for many flavors of motors, from <10W for an air blower to many kWs for an electrified drive train, and many others in between. The key to optimizing the motor drive for each application lay in careful selection and control of the power switches. Traditionally, lower power applications have employed Si-based MOSFETs, and higher-power applications have utilized Si-based IGBTs. However, in recent years (and certainly looking to the future), the power switches have been migrating to wide bandgap parts, such as those made from GaN and SiC.

These kinds of requests are very common and often come with frustration from designers who must design solutions for the different gate-drive voltage requirements of each power switch type. RECOM empathized with the challenge before the PDM and understood how challenging designing and qualifying an isolated gate driver for a single switch type can be, let alone all of the above. This is why they introduced a brand-new, universal isolated gate driver that can be easily programmed for any of the mentioned switch types (and even has the flexibility to support some yet-to exist) with an identical solution that only requires changing four resistors to program the appropriate, asymmetric supply voltages for each switch type. The R24C2T25S supports all 24 inputs, making it compatible with today‘s 12V main bus and the next generation 24V main bus.

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