Power design needs future proofing

Future-proofing system design by allowing for next-generation power is a key element in connector selection, says Herbert Endres of Molex

Although the trends for higher data rates and greater signal densities of the connector tend to attract most of the focus in the electronics industry, recent demands on the modest power connector have brought it into the limelight, especially in server and storage applications.

Here, the increased data rates and higher currents associated with ever-shrinking power supplies intensify the need for connectors to support currents from 50 to 150A. Furthermore, demand for high-current connectors for solar power technologies and the development of hybrid or electric vehicles is rising at a significant rate.

In conjunction, each new generation of high-performance server platforms or switching power supplies necessitates higher airflows, to cool the increased number and even faster semiconductors. As voltages in silicon have fallen to accommodate the faster gate speeds, the current needed to power those devices has increased exponentially. Thus, connector current densities, voltage drop, inductance and packaging flexibility have become more critical than ever to the power engineer. Power integrity is the discipline used to optimise all of these factors into a comprehensive solution to system architecture.

The most familiar challenge for a designer is to fit more watts into the same or less amount of space. For example, today the need might be for an 850W, 12V power supply, but tomorrow’s design may call for a 1,200W, 12V power supply in the same enclosure. Using a simple power formula (I=P/E) shows us that if you were to use a traditional six-blade power connector rated at 30A/blade (120A/25mm), the 850W power supply would work just fine (850W/12V = 70A), so 70A power and 70A return over the six power blades will yield about 24A/blade. But that same power supply putting out 1,200W would require about 34A/blade on that same connector. So what are the choices? Add two or more power blades and go outside of the mechanical envelope? Use the same six-blade connector with an elevated T-Rise and push above the manufacturer’s ratings, or change the connector to a higher capacity connector?

Unfortunately, many power supply manufacturers and OEMs alike chose to stay with the same connector running at elevated T-Rise levels and accept the risks associated with going over the agency rating of the connector. This is because choosing a new connector would mean increasing the size of the connector, impeding airflow and/or slightly increasing power supply cost.

The real choices regarding this problem are rooted in power integrity, specifically: copper thickness (weight) on the PCB; airflow around the interconnect area and through the power supply; connector packaging design (more power, less space); contact design and material selection; and cost.

Power integrity is the conscious optimisation of each one of the points above, providing the most effective solution for the electrical and thermal environment. Additional copper thickness and/or increased airflow can increase the current capacity of the connector (albeit with an added cost). Whereas a better connector design can provide the same or more current per 25mm in a smaller package, alleviating the need for bigger fans and more copper.

That begs the question, why is connector height so important? Basically, less height means more airflow, and more airflow keeps the interface cooler, increasing current carrying capacity at a typical 30° T-Rise. Airflow is being factored more and more into the thermal design of new systems.

As a rule of thumb, for every 100W of power needed to power the system silicon, 50 additional watts are needed to cool the system from the heat generated. So, if system architects and thermal management engineers can allow heat to escape more freely and effectively, the power needed to actually cool the system can be reduced — hence, less power consumption.

Designers should consider power integrity as a key factor when selecting the right power connector. Molex is a power interconnect company that can provide solutions to these challenging system design goals.