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issue: March 2004 APPLIANCE Magazine

Motor Technology
Flash Microcontrollers for Motor Control

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Microchip Technology's new 8-bit microcontrollers are said to be reliable, quiet, and energy efficient through advanced analog and digital feedback and a Pulse Width Modulation (PWM) control system.

Microchip Technology of Chandler, AZ, U.S. has introduced a family of 8-bit Flash microcontrollers (MCUs) with advanced motor control peripherals designed to improve efficiency and extend motor life in several applications, including appliances.

Microchip Technology's new MCU product family is said to be the only MCU that has hardware available to drive three-phase motor control applications. The devices contain 256 bytes of on-board, high-endurance data EEPROM, and up to 10 MIPS performance at 40 MHz. The MCUs have a 16-level programmable low-voltage detection module and nanoWatt Technology feature that provides enhanced power-management capabilities.
The new PICMicro MCU family contains three modules specifically designed for advanced motion and power-control applications, which are key to improving the efficiency in motor control applications, says Cheri Keller, product marketing manager of Microchip Technology's Advanced Microcontroller and Automotive Division. The first module is a 14-bit power control PWM. The second is a high-speed analog-to-digital (A/D) converter that can be synchronized with the PWM. The third module has motion-feedback capabilities and contains a quadrature encoder, which is used to track the speed and position of the motor. "These three features can be used in a closed-loop a.c. induction motor (ACIM) and brushless d.c. (BLDC) motor applications, thus providing improved efficiency, quieter operation, and more reliable operation," Ms. Keller notes.

Appliance designers and engineers are able to eliminate the use of external A/D converters, resonators, PWM controllers, and quadrature encoders because the three modules are available within the MCU, which lowers the overall component costs and the PCB costs due to board space savings.

The advanced power control and motor control applications can be used in the appliance industry for items such a dishwashers, refrigerators, washing machines, and ventilation fans. The new MCU devices include up to eight PWM channels with 14-bit resolution, center alignment, programmable dead time (950 to 250 ns), and two external fault-protection inputs. They also have capture/compare/PWM modules, an internal PC oscillator with eight selectable frequencies that range from 8MHz to 31.25 KHz, and an enhanced USART supporting RS 485, RS232, and the LIN protocol.

The flexibility of the modules allow designers to add variable-speed control that can improve efficiency by 30 percent in some appliance applications - such as a refrigerator compressor - by controlling the pace at which it operates, Ms. Keller tells APPLIANCE. "Rather than turn the motor completely off and then back on to full speed, which takes a great amount of power, designers can incorporate variable-speed control through the use of a PWM module," she explains. "This significantly reduces the amount of energy needed to operate the motor, just by varying the speed."

Any MCU in the series can be used in conjunction with a drive to provide the variable-speed control. "The PIC18Fxx31 family also [incorporates] the use of fail-safe clock monitors that use the internal Resistor-Capacitor (RC), a back-up clock, in the event an external clock were to fail," Ms. Keller says.

"In addition," she continues, "there are two external fault pins that can be used to safely shut down the motor in the event there was some sort of disturbance to the motor."


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