Electronic Design

Power> A Series Of Facelifts Simplifies On-Board Architectures

In the past several years, we have seen a remarkable shift in board power distribution and management. Probably the most noteworthy trend was the proliferation of product choices for on-board power system designs. We quickly moved from supplying a few separate voltages to the circuit board to the distributed power architecture (DPA), where a single voltage is supplied to several isolated dc-dc converters that generate the required lower voltages.

As the level of voltages decreased and the number of voltages increased, the intermedi-ate voltage bus architecture (IBA) quickly followed DPA. It's now rapidly becoming a de facto design approach for new on-board power distribution. In such systems, a single isolated front-end dc-dc converter (FE) provides power to multiple point-of-load converters (POLs) that are interspersed across the circuit board.

When the voltage sources were still located within a single module, control was local and fairly straightforward, and there was no need to provide many control functions. With the increase of separate converters on the board, the next challenge was to control and manage the multitude of POL converters scattered across the circuit board.

The need to sequentially control each voltage and monitor the output integrity opened a market for separate discrete IC controllers and monitoring devices. Designers often used discrete devices, such as control ICs in conjunction with several FETs and resistors, to monitor and control the output voltages and currents.

While such separate controllers fulfill the control and monitoring functions, they require many external components. Moreover, they take up valuable circuit-board real estate, are difficult to interface with dc-dc converters, and require careful design considerations.

The incorporation of the control and monitoring functions into the POLs eliminates the need for external FETs and current monitor resistors. Yet it still leaves the need for a sequencing controller and the associated interface issues.

Incorporating the control circuitry into the front-end dc-dc converter as well greatly reduces board space and the cost of both components and assembly, significantly simplifying IBA system design and development. Using fewer components also boosts system reliability and lowers the cost of inventorying and handling multiple components.

Adding controls and monitoring circuits into the dense and thermally hot packages increases the complexity of converter designs. With lower voltages, tolerances of the monitoring circuitry need to be narrow and stable. This, in turn, dictates that such circuits be thermally isolated from the hot switching components.

As the requirements of different control and monitoring functions increase, the circuitry will become very complex and gravitate toward digital control. Being able to process more data and provide additional functions will give system designers multiple choices not previously available or affordable.

Despite these difficulties, functions that were once separate ICs eventually will be incorporated and provided as standard features of the new FEs and POLs. By anticipating the trend to integration, companies such as Power-One are already providing dc-dc converters that incorporate many of the needed control and monitoring functions. The converter products that are now in development will go a step further, providing all of the required functions while also working seamlessly with one another.

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