Motor control applications are shifting into higher gear, buoyed by advances in the power ICs that turn on the motor, the microcontrollers that drive the system and the design tools needed to speed the system's time-to-market.
With applications such as automotive electronics now demanding faster and more computeintensive semiconductor solutions, integrated controller systems based on digital signal processors are coming on quickly. Design tools, over and above the currently available DSP development tools, have also been stepped up a notch to allow the OEM to focus more on motor control as a basic black-box challenge.
In addition, conventional microcontroller-based (non-DSP) systems, often identified with general-purpose applications, are becoming more sought after as they move into 16-bit territory as a lower-cost alternative to DSPs for fairly high-performance tasks. Power semiconductor vendors are bringing power switches to market that may contain control logic, gate drivers and internal MOSFETs. The parts are aimed at stepper and dc motors for printers, robotics and automotive-electronics subsystems. Many of the devices have built-in current limiting, thermal shutdown and undervoltage shutdown protection circuitry.
The future seems brightest in automotive applications, where many of these devices are headed. "Automotive is an explosion ready to happen," said Dave Wilson, tech specialist and motor products evangelist for Motorola (Phoenix). "Possibly half of all motor control opportunities will be in automotive by the end of the decade." Consumer and industrial applications are also strong, observers said.
In many cases, the migration is toward 32-bit systems for high-power processing, notably in power-steering and transmission applications requiring smooth control. As in other power-related applications, the DSP approach offers cost/performance benefits.
With DSP control, the ongoing goal for vendors is to bridge the gap seamlessly by offering users semiconductor and subsystem solutions that have the DSP's computational power and the traditional microcontroller's programming friendliness and overall functionality. Many of these solutions are in the evolving smart-power-module and system-on-chip efforts, which are becoming standard design approaches throughout power electronics. They integrate DSP cores with flash memory and functional system blocks, such as pulse-width modulators and A/D and D/A converters, to cut chip count and system cost.
"For cost-sensitive applications, DSP and an integrated solution is the only option," said Finbarr Moynihan, product line manager at Analog Devices Inc. (Norwood, Mass).
Among the newest DSP-type entries are Motorola's 56F83x family of devices, now in sampling. An extension of Motorola's existing 56800 family, the devices integrate the company's newer 56800E microcontroller/DSP ("hybrid") core with up to 256 kbytes of flash memory, which is used for storing operating programs and updated system variables. Intended to provide a natural migration path for current users of the company's 8- and 16-bit microcontrollers, the family provides 60 Mips of processing power with flash memory and as much as 120 Mips in a RAM-based chip. Actual system speed is a function of throughput at control ports for automotive, instrumentation and industrial applications.
The products operate over an extended temperature range of -40 degrees C to 125 degrees C and will be available in six models, priced from $2.50 to $20 each. The 56F83x devices provides 32-bit performance with 16-bit code densities, according to the company. Among the targets are 16-bit-MCU users requiring additional processing power.
Another entry is Texas Instruments Inc.'s 32-bit, 150-Mips TMS320F28x DSP, with up to 128 kwords of flash memory (yielding 120 Mips at 256 kbytes, or 150 Mips when RAM is used), plus A/D, and control and communications peripherals. TI (Houston) said the new DSP runs at four times the speed of its predecessor. It is priced at about $18 to $23 in quantities of 1,000.
Meanwhile, Analog Devices, which launched its ADSP-2199x family last year, has added more memory and a controller-area network (CAN) bus to its 21992, which was introduced in August.
Even as DSP-based solutions advance, vendors are looking for a still-greater edge. International Rectifier (El Segundo, Calif.), teaming with Xilinx Inc. (San Jose, Calif.), has applied a field-programmable gate array as a processor, which is a step beyond the FPGA's usual association with system peripheral devices. Up until now, the FPGA's cost and current draw have been largely considered objectionable.
The Accelerator design platform, using Xilinx's Spartan-IIE FPGA, is based on the idea of a customizable mixed-signal chip set that effectively links all the system's parts: analog, digital, peripheral and power. The design platform, analogous to IR's use of multichip modules as first applied for dc/dc converters, includes all hardware for a 1.5-kilowatt servo amp, preloaded code in E2PROM for the FPGA and Windows-based configuration software called ServoDesigner.
"If you know what the algorithm is, then you can apply the FPGA as a parallel processor to gain a 10x advantage in processing power over programmable DSPs," said David Tam, vice president of applications engineering and systems architecture. "The peripheral devices in the traditional programmable DSP or microcontroller chip cannot change.
"What we have with the FPGA is a configurable DSP, which means you can program and reprogram the system's engine and analog and peripheral elements, all at the same time. And that's more than just configurable power. It gives you much more freedom to talk to the analog and peripheral sections."
Microcontroller-based systems also continue to make headway to simplify motor design and speed time-to-market. Microchip Technology (Chandler, Ariz.) has just introduced four flash microcontrollers in its PICmicro PIC18F family that add an open-loop kernel for single-phase motors. The PIC18F2439, -2539, -4439 and -4539 are intended to simplify programming for end users who have little experience in motor control techniques.
"The PIC18FXX39 family merges all the advances of the PIC18F architecture and the flexibility of flash program memory with a sophisticated single-phase motor control kernel that provides a quick solution for engineers," said Cheri Keller, product-marketing manager at Microchip.
The devices contain 12 to 24 kbytes of flash memory and two 10-bit PWMs, and they provide up to 10-Mips performance at 40 MHz. They feature three all-purpose 16-bit timers, an A/D converter (with up to eight channels) and an addressable universal synchronous/asynchronous receiver/transmitter (USART) module supporting RS-485 and RS-232. The devices are priced between $4.28 and $5.15 in volume quantities, depending on the version. For development, the company offers its PIC18F2539 motor control evaluation kit.
Other devices due out soon include 8-bit microcontrollers from Fairchild Semiconductor (San Jose), targeting thermally critical motor applications and DVD/VCR applications.
When it comes to turning on the motor, power ICs also continue to advance. STMicroelectronics (Lexington, Mass.) is one of the first vendors to implement the idea of the design platform for quick customization of the silicon with its powerSpin smart motor power family. The L6205-7 dual H bridges, L6208 dual H-bridge drive and L6235 three-phase bridge were launched last year for stepper and dc motor applications. They are intended for 2.8-amp (5.6-A peak) service, ST said.
The powerSpin platform will soon expand to include a family of devices offering various mix-and-match features and providing half the current to serve the growing roster of lower-current applications, according to the company.
Other new power switches include Motorola's MC33886 and MC33887 H bridges, based on the company's SmartMOS technology, for use with Motorola's line of MCU and DSP chips. The switches include control logic, a charge pump, gate drivers and internal MOSFETs. They also have have built-in current-limiting, thermal-shutdown and undervoltage-shutdown-protection circuitry. Motorola said that the H bridges are suited to stepper and dc motors as applied to printers, robotics and automotive applications.
Allegro Microsystems (Worcester, Mass.), probably best-known for its work with stepper motors, has made its first foray into the high-power automotive and industrial market.
"Everyone's watching the 42-volt market and 100-amp applications, although they're not developing as fast as most everyone expected," said Steve Lutz, director of the company's IC business unit. In the meantime, Allegro's A3935 power MOSFET predriver IC, for three-phase brushless dc motors, is designed for 135 degrees C under-the-hood applications such as engine cooling and power steering. The bipolar-CMOS-DMOS part has six outputs to drive external power MOSFETs independently for implementing sinusoidal control of the brushless dc motor. The part is suited for operation with up to 40-V systems and includes fault operating and diagnostics, with short-to-battery and short-to-ground detector circuitry.
Another new product, Allegro's A3965, has two H bridges capable of output currents to plus/minus 500 mA (6- to 20-V operating voltage) for portable and battery-operated stepper motors.
The company has also added the A3967 to its EasyStepper family for bipolar 30-V stepper motors that require up to plus/minus 750 mA in commercial, medical and industrial environments. The family features a simple two-line interface (vs. up to as many as eight in traditional architectures) for controlling step and direction. The stepper motors can be advanced in full, half, quarter and eighth steps. Microsteppers of this sort are expected to open the way soon to routine 16-step applications, which will provide quieter operation in high-end vehicles.
Virtually all vendors provide application assistance and evaluation boards. Now, menu-based programs are becoming more motor-centric (as opposed to microcontroller- or DSP-centric)-slowly migrating toward the systems level, allowing users to specify parameters in black-box fashion and making DSP coding more transparent.
Motorola took a step in that direction with its menulike Processor Expert. The tool uses Java-like "beans" that correspond to various functions, such as a PWM peripheral or LED output. It will be available for the company's DSP-type systems later this year.
Analog Devices Inc.
Allegro Microsystems Inc.
Microchip Technology Inc.
Motorola Semiconductor Products Sector
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