Power Electronics

Industrial MCUs Offer New Options for Motor Control

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Industrial and automotive applications are driving the development of microcontrollers with the performance capabilities and peripherals needed to control a wide variety of motors and actuators. Through multichip designs and monolithic integration, the new microcontrollers simplify system-level design by bringing a variety of functions on chip or in-package. These functions include serial communications such as CAN or LIN, analog signal processing, output power stages, and power supply and power protection circuitry. Recent product introductions from Freescale Semiconductor, STMicroelectronics and Microchip Technology illustrate these trends.

Two years ago Freescale Semiconductor introduced its family of intelligent distributed controllers (IDC). These devices use the system-in-package approach to combine a HC908 flash microcontroller chip with a SmartMOS analog chip in a 54-pin SOIC. The latter chip integrates the LIN physical layer with other analog and power functions.

Recently, Freescale expanded the IDC family with its introduction of three devices — the MM908E621/22/26 — targeting automotive and industrial applications. The new IDCs are designed to simplify system design, while reducing board-space requirements in controls for automotive seats, mirrors, window-lift controls and door locks. These devices also may find use in robotics, vending machines and paper printers for point-of-sale terminals.

According to Rod Borras, analog senior market development engineer at Freescale, the IDCs may either be viewed as “intelligent analog chips” or as “microcontrollers with power outputs.” The devices allow system designers to control motors and other actuators by simply addressing registers on the MCU, which features 16 KB of flash and 512 bytes of RAM. The IDCs also protect against overcurrent, overvoltage, undervoltage and overtemperature conditions.

The MM908E621/22 feature four half-bridges and three high-side outputs with position and temperature-sensor drivers. The devices offer complete control of a high-end mirror with adjustable fold/glass position, heater, side turn flasher, pedal lamp, and temperature-sensing and position-memory functions. The electrochome feature, which enables mirror dimming, differentiates the MM908E622 from the '621.

The MM908E626 features four half-bridges, enabling direct control of three dc motors at up to 3 A. The device can also be configured to run bipolar stepper motors in adjustable current control mode up to 600 mA. Qualified for applications up to 115°C, the MM908E626 is essentially a high-temperature version of the previously introduced '625. However, it should be noted that the '625 had a single high-side output not found on the '626 (Fig. 1). The other previous member of the IDC family is the MM908E624, which features three high-side switches. Members of the IDC family specify operation from -40°C to 85°C. In quantities of 10,000, unit pricing is $4.69 for the MM908E621, $4.17 for the MM908E622 and $4.64 for the MM908E626.

In contrast to Freescale's system-in-package approach, STMicroelectronics opted for the monolithic approach in developing what it calls the first industrial microcontrollers based on 32-bit ARM7 core. The STR730F series addresses the emerging demand for 32-bit microcontrollers in industrial applications such as factory automation, appliances, test and measurement equipment, point-of-sale terminals and security systems. These applications require both high-performance from the MCU and low cost.

A key feature of the new microcontroller is its ability to operate off of a single 5-V supply rail, which is the preferred supply configuration for industrial applications that require good noise immunity. In addition, the STR730F MCUs are specified over the extended -40°C to 105°C temperature range.

The new microcontroller family delivers high performance via a 32-MIPS ARM7TDMI RISC processor core, full-speed (zero wait state) access up to 256 KB of embedded Flash memory, and a 16-channel DMA facility that reduces the CPU load in complex applications.

In addition, the chips feature peripherals such as three independent CAN controllers, a fast (3-µs), 16-channel/10-bit A-D converter, and up to 16 PWM outputs capable of supporting multiple single-phase or three-phase motor-driving requirements. Other features include a full complement of industry-standard serial communications interfaces, a real-time clock, two embedded voltage regulators and five low-power modes.

Packaging options include a 144-pin TQFP, a 100-pin TQFP and the 10-mm × 10-mm 144-lead BGA. The STR730F devices are now sampling. In quantities of 10,000, unit pricing ranges from $4.53 for the STR736FV0 (TQFP100, 64-K memory size, No CAN, 4xUART, and 12x PWM) to $8.99 for the STR730FZ2 (TQFP144, 256-K memory size, 3x CAN, 4x UART and 16x PWM).

Another vendor, Microchip Technology, recently introduced a family of 16-bit digital signal controllers (DSCs) that includes models optimized for motor control and power conversion. DSCs target embedded designs that require high levels of performance, memory and I/O without the complexity of traditional digital signal processors.

Microchip's new dsPIC33 family operates at 40 MIPS, with family members offering 64 KB to 256 KB of self-programming Flash, 8 KB to 30 KB of RAM and 64- to 100-pin packages. Other features include a choice of serial interfaces including up to two each of SPI, I2C, UART and CAN. The chips operate from a 3.3-V supply.

Within the dsPIC33 family there are 12 devices optimized for motor-control and power-conversion. These ICs feature one or two 1.1-MSample/s A-D converters, up to 8 sample and holds for simultaneous sampling, and a quadrature encoder interface. Applications for these DSCs include sewing machines, LED lighting arrays, washing machines, access control, online UPS, environmental control, electronically assisted power steering, precision manufacturing equipment, absolute encoders and resolvers, inverters and electric vehicles. General sampling of the dsPIC33 family is expected to start in the first quarter of 2006, with production expected in the second quarter.

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