FEATURE AUTOMOTIVE ELECTRONICS
HOW TO POWER 48V SYSTEMS IN MILD HYBRID VEHICLES Thomas Elies, manager product marketing MOSFETs at Infineon’s Automotive Division
heatsink to be mounted directly to the top of the package, significantly shortening the heat flow path and improving the system’s thermal performance. This allows the power to be increased by more than 20 per cent or the cooling effort to be reduced accordingly.
In addition, because of the reduced heat flow into the PCB, boards with lower glass transition temperatures can be used. Furthermore, system designers can place components on the backside of the board, saving overall board space.
W
hen it comes to alternative drive systems, this decade will lead to a major turning point: By 2030, market research expects the majority of all new cars sold to have a fully or partially electric drivetrain. While the public focus is usually on battery electric vehicles, 48V mild hybrids will show the steepest growth. Besides a better fuel efficiency compared to conventional cars, 48V systems also increase performance and comfort. To fully exploit this potential, the right choice of power semiconductors is essential. For car manufacturers, 48V mild
hybrids represent a rather quick way to reduce CO2 emissions to some extent. They support regenerative braking and electric support of the combustion engine. Furthermore, a 48V supply allows additional systems to run more efficiently than on 12V – leading to a further increase in fuel efficiency. These systems include e-turbos, e-compressors, auxiliary heaters and certain pumps and fans, for example. In addition, carmakers implement 48V
systems in order to increase driving comfort and performance. For example, while electrifying roll stabilization with a 12V system is not ideal because it requires very high power, a 48V system can turn it into a powerful electrified chassis feature.
NEW MOSFET PACKAGES FOR THE 48V ARCHITECTURE When it comes to the power stage ICs, low-loss 80V or 100V MOSFETs are the common choice for 48V systems. The specific requirements may differ, depending on the application and its design. The three main 48V applications are the starter generator, the 12V/48V DC/DC converter and the battery disconnect switch.
14 JUNE 2020 | ELECTRONICS
Infineon addresses them with the TOLx package family. It is based on the high performing low voltage TO-Leadless package (TOLL). Not having package leads contributes to low resistance and inductance values and a compact size. TOLL is capable of 300A DC current, offering best-in-class on-resistances of maximum 1.2mOhm (80V) and 1.5mOhm (100V), and has a 10x12mm footprint.
DIFFERENT BOARD, DIFFERENT PACKAGE While system designers most commonly use FR4 boards, there are other options, too. However, with different substrates, package requirements may change. For example, different coefficients of thermal expansion with copper and aluminum lead to differences in material expansion. Therefore, using the same packages on an IMS board with an aluminum core leads to increased stress on the solder-package pin connection, which might cause cracks in the solder joints and a degradation of electrical and thermal performance. To solve this problem, Infineon added
the TOLG package to the TOLx family. It has additional gullwing leads for the source and gate connections. They give the package extra flexibility, increasing the reliability on an Al-core IMS board.
TOP-SIDE COOLING FOR A HIGHER PERFORMANCE A third member of the TOLx family will go into production in early 2021: the TOLT package, the T standing for top-side cooling. It has been designed for systems that are very demanding in power density, where thermal performance and cooling systems are extremely important. In the TOLT package, the leadframe is flipped so that the drain pad is exposed to the top of the package. This allows for the
NEXT STEP CHIP EMBEDDING In order to enable the next step in system efficiency, Infineon has partnered with Schweizer Electronic AG to develop power MOSFET chip embedding. With this technology, the MOSFETs are no longer soldered onto the PCB but integrated within. The thermal and electrical advantages of embedding the chips enable a significantly higher power density. At the same time, reliability can be increased, specifically in comparison to ceramic modules, while the complexity in assembly and joining technology is reduced. This allows developers to either increase the performance of a 48V system by up to 60 per cent or make it more cost-effective.
THE FUTURE OF 48V Infineon
www.infineon. com
Mild hybrids are clearly only one first step towards CO2 regulation targets. Alone, they will not do the trick, which is why carmakers are investing billions in fully electric cars. In fact, some see 48 V systems only as bridge technology. However, with the benefits in auxiliaries, there are good reasons also outside of the drivetrain to implement 48V systems. Furthermore, some commercial vehicles with a payload of up to 1,000 kg already implement a fully electric drivetrain based on a 48V supply. This may well work also in future urban mobility concepts where driving at low speed across short distances is the norm.
/ ELECTRONICS
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