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DSCs combine best of MCUs, DSPs

Posted: 03 Sep 2007 ?? ?Print Version ?Bookmark and Share

Keywords:DSCs? control-oriented peripherals? DSPs? pulse-width modulators?

Digital signal controllers (DSCs) are a new class of processor that combines the best attributes of MCUs and DSPs.

Like MCUs, DSCs have fast interrupt responses, offer control-oriented peripherals such as pulse-width modulators and watchdog timers, and are programmed in C. They also incorporate DSP features such as single-cycle multiply-accumulate (MAC) units, barrel shifters and large accumulators.

DSCs are used in a range of applications, but most go into motor-control, power-conversion and sensor-processing applications. The main motivation for using DSCs in such applications is to reduce power consumption. The largest power savings from using DSCs could come from converting fixed-speed electric motors to variable-speed motors. Variable-speed drives, which require the DSP horsepower found in DSCs, consume roughly half the energy of fixed-speed drives.

Power-saving potential
That presents a huge opportunity to save power, since fixed-speed drives are widely used. For example, the ABB Group estimates that two-thirds of industrial electricity is used to power electric motors and that nearly all of those motors use fixed-speed drives.

DSCs can also be used to replace mechanical systems with more efficient electronic systems. For example, cars contain many mechanically actuated systems, such as power steering, fuel pumps and water pumps. Those can be replaced with systems that use electric motors. Doing so reduces energy consumption and emissionstwo areas of increasing concern for automakers.

Power conversion is another source of power savings. For example, data centers usually require two power supplies per server for the sake of redundancy, and the supplies must be sized to support peak power requirements. That means that each supply operates at much less than 50 percent capacity under normal loads.

Parts pack all these features for under $12. Click to view full image.

Intelligent strategies
Analog-controlled supplies become inefficient at low loads. In contrast, digitally controlled supplies can maintain efficiency by using "intelligent" strategies such as shedding phases.

The use of DSCs has grown considerably in recent years, and many expect the growth to continue. "Putting a programmable DSC into the control loop in applications such as motor control opens up a world of possibilities for system designers," said Jeff Bier, president of independent analysis firm Berkeley Design Technology Inc.

"I believe DSCs will do for motor control and other control-loop applications what DSPs have done for communications and multimedia applications: improve performance, enable new features and provide flexibility for designers, while ultimately reducing costs," Bier added.

The top three DSC vendors are Texas Instruments Inc., Freescale Semiconductor Inc. and Microchip Technology Inc., according to Forward Concepts. Those companies dominate the DSC market, with other vendors such as Infineon Technologies AG and Renesas Technologies Corp. taking a small slice of the pie. However, not all vendors have adopted the term DSC. For example, Infineon and Renesas refer to their DSCs as MCUs.

The DSCs on the market range from low-end parts priced at $2 to high-end devices costing upward of $20 for 1,000 volumes.

- Kenton Williston
DSP DesignLine

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