Power Electronics

Part One: Power Distribution Leads to Multiple On-Board Bus Paths

Despite the warning in the popular Frank Sinatra song “Fools Rush In Where Angels Fear to Tread,” I will be very brave and attempt to look into the future of on-board power distribution trends.

Forecasting trends is like walking on ice. The closer you are to the shore, where the ice is thickest, the more solid your predictions are. As you venture further into the future, the closer you get to the center of the lake, where the ice is wafer thin. There, predictions become more precarious.

By carefully examining and then projecting trends, without stepping too far onto the thin ice, we just might catch a glimpse of the power-handling progress that will be achieved by 2020.

As we all know, power converters provide power mostly to microprocessors and integrated circuits (ICs). The trend of such ICs and microprocessors has been a continuous increase in power consumption combined with a lowering of the voltages and increases in current usage. As long as silicon is the base material for such devices, the trend will continue and devices that power them will have to accommodate their ever-greater requirements.

This in turn means that there will be an increasing need to develop higher efficiency, denser and more thermally efficient converters.

On the other hand, there’s a possibility that other methods such as optical computing could emerge. Or, perhaps there will be devices that do not require power in the way that traditional ICs do. If either of those cases comes to be, then power supplies will take quite a different direction.

I feel that within the next 20 years there is a strong probability silicon will remain the computational vehicle for IC processors. That being said, solutions to the power-conversion needs of ever-increasing power on the circuit board will have to be solved by the power-supply industry.

A distributed power architecture (DPA) — where a single voltage, supplied to several isolated dc-dc converters, generates the required lower voltages on the board — has already been replaced by an intermediate bus voltage architecture (IBA). In an IBA, a single isolated front-end dc-dc converter (DC-DC FE) provides power to multiple point-of-load converters (POLs) interspersed across the circuit board.

In the near future, this trend will continue, with only the number of individual voltage and current requirements increasing, with the resulting number of POLs on the circuit board also increasing.

A DC-DC FE will still provide the required bus voltages and isolation from the input power. They will become more efficient, dissipate less power and operate at lower temperatures. Internally, they might consist of a bank of converters operating in a phase-shifted mode, which in turn will allow for smaller inductive and capacitive components.

An IBA, rather than being a single trace carrying a large current, could splinter into multiple traces that will each carry a smaller current or a different voltage. Some designs today are contemplating using two buses: a 12-V bus to power devices that need 3.5 V and higher voltages and a 5-V bus to power devices that require lower voltages.

In such a multiple-power-paths architecture (MPPA), the power paths will be managed by intelligent controller gates (ICGs), which will channel the power through the proper path. Parallel processors as well will be distributed throughout the board, and power will be channeled as needed by each processor. Idle processors could be turned off or could run at standby currents.

In this part of the article, part one, I discussed the electrical power distribution on the circuit board. Next month I will cover the issues of circuit-board layout and cooling and will address some of the system interface issues.

If you have any comments or suggestions, please e-mail me at [email protected].

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