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Safety Requirements Specification

Now that you have confirmed the boards work properly, you can decide when to use the tester system to in an application. In my experience, the general rule for deciding between building a traditional PC-based test system or a microcontroller-based system, it all comes down to cost, complexity and urgency. If you need a simple low-cost tester, then consider building your own. Overton Claborne is president of Overton Instruments where he develops custom test equipment using embedded systems. E-mail: overton@microate.net.

This article originally appeared in Test & Measurement World, in May, 2012, as Build a microcontroller-based functional tester.

MF2DL1000DA4/02J_NXP USA Inc._RFID, RF Access, Monitoring ICs

Efficiency, reliability and size: Power electronics is being optimised with regard to environmental awareness and policy. It is instrumental to future mobility based on hybrid technology and electric vehicles, and plays a key role in the fight against increasing emissions and waning resources. Particularly important in this context is the implementation of higher power densities, reduced volume hand in hand with improved reliability. Current packaging technology faces technical limitations. The task at hand is to overcome the following limits of current packaging technology: Solder joints, module base plates, module layout, chip temperatures, and current densities.

MF2DL1000DA4/02J_NXP USA Inc._RFID, RF Access, Monitoring ICs

Solder joints In a conventional soldered power module with a copper base plate, the solder joint is often the weakest mechanical point in the overall system. Due to the materials’ different coefficients of thermal expansion, high temperature changes and changing electrical loads during operation, fatigue effects may result in the solder layers of the module. Signs of this are the high thermal resistances during operation, which in turn lead to higher chip temperatures. This interaction process will ultimately lead to component failure as a result of bond wire lift-off. A further reliability risk in soldered PCB connections is cold joints.

Base plates Base plates for modules with large dimensions, and thus more power, are costly and technically difficult to achieve in regard to thermal and mechanical performance. The one-sided substrate soldering results in a bimetal effect that causes non-homogenous torsions, meaning the thermal connection to the heat sink is not ideal. In place of an ideal heat sink connection with quasi-metal contact, the gap between base plate and heat sink has to be filled with thermal paste which has poor thermal properties. The result is a barrier in the overall thermal system. The thermal paste has a thermal resistance that is 400 times higher than that of copper, and this layer is responsible for up to 60% of the thermal resistance between chip and coolant.

MF2DL1000DA4/02J_NXP USA Inc._RFID, RF Access, Monitoring ICs

Module layout For modules for 150 A and above, the chips have to be connected in parallel to the DBC in order to enable higher current ratings. Due to the mechanical restrictions in the layout in conventional base plate modules, ideal symmetry is often not achievable. The result is non-homogeneity in the switching behaviour and different currents at the chip positions. For this reason, the data sheets specify the weakest chip only. Internal designs based on bond wires or connectors have a negative impact on the conducting resistances in the module and lead to higher stray inductance.

Chip temperatures Advancements in IGBT technology enable finer IGBT cell structures and thus smaller chips. This development is also being driven by the pressure to reduce the cost of power semiconductors. Smaller chips go hand in hand with an increase in current density, with chips becoming on average 35% smaller in recent years. At the same time, the maximum junction temperatures have been increased to 175°C. This means that the modules can be even more compact. On the other hand, however, this also means an increase in the temperature gradient between IGBT and ambient temperature, causing greater stresses on the materials. A 25K increase in temperature will reduce reliability by a factor of 5. What is more, new materials such as SiC and GaN allow for even higher temperatures.

The different branches themselves will run on MOST150, with the add-on option that each branch can be hot plugged or cut off without impacting data communication within the rest of the system. Of course, each branch may again consist of a ring itself, or a daisy chain, in case the Dual-Port INIC is used. With such an architecture, those use cases which require a true star architecture, e.g. coming from the driver assist domain, are addressed, while at the same time maintaining the principal advantages of MOST, including the synchronicity and the low latency of the network.

It has always been a particular strength of MOST to not shoot for the highest bitrates technically possible, but rather find the appropriate 'sweet spot', as discussed previously. Instead, the development of new functions and features, speed grades and physical layers has always been driven by the MOST Cooperation, collecting the real market requirements of a broad community. In fig.3 the driving functions for Most25, Most150 and also the future generation are shown.

The absolute speed grade for the future generation of MOST is not entirely determined yet. The same applied for MOST150 at the time: It was clear that a bandwidth of more than 100 Mbit/s would be required, but the exact bandwidth was determined by other parameters, e.g. the strong requirement of keeping the POF and the connector system identical to MOST25.

Technically, the feasibility of implementing a speed grade in the range of 5-10 Gbit/s for a next generation has been investigated already. As discussed previously, the even more interesting question is: What does the automotive market really need? Why would people like to transport data at such high speed and which data shall be transported at all?