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

Like microcontrollers, 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 the majority go into motor control, power conversion and sensor-processing applications. The main motivation for using DSCs in such apps 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, because 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.

Digital signal controllers can also be used to replace mechanical systems with more-efficient electronic systems. For example, automobiles contain many mechanically actuated systems such as power steering, fuel pumps and water pumps. Those systems can be replaced with systems that use electric mo-tors. Doing so reduces energy consumption and emissions--two 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 each supply operates at much less than 50 percent capacity under normal loads.

Analog-controlled supplies become inefficient at low loads. In contrast, digitally controlled supplies can maintain efficiency by employing "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 like motor control opens up a world of possibilities for system designers," said Jeff Bier, president of independent analysis firm BDTI.

"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.

In order of market share, the top three DSC vendors are Texas Instruments Inc., Freescale Semiconductor Inc. and Microchip Technology Inc., according to market research firm Forward Concepts. Those companies dominate the DSC market, with other vendors such as Infineon and Renesas taking a small slice of the pie. (It should be noted that not all vendors have adopted the term DSC. For example, Infineon and Renesas refer to their DSCs as microcontrollers.)

The DSCs on the market range from low-end parts priced at $2 to high-end devices costing upward of $20 (all prices in this article assume 1k volumes).

The table is limited to devices from the three major DSC vendors that are priced at $12 or less, include on-chip flash and target sensorless motor control--the single-largest DSC market.

Kenton Williston (kentonwilliston@yahoo.com) is site editor of DSP DesignLine (www.dspdesignline.com) and president of Cabral Consulting.

Seth Benton, an analyst at Cabral Consulting, contributed to this article.

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