Part 3 ― Motor Control Solutions for Key Application Sectors

Home Appliances ― M16C/Tiny Microcomputers Facilitate the Design of Quiet, Energy-efficient Refrigerators, Washers, and Many Other Products

Within the home appliances sector there are an extremely wide range of product categories with numerous variations and for many of them, features like energy efficiency and quiet operation are absolute requirements. Those characteristics can be implemented by motor control functions built with the microcomputers in the 16-bit M16C/Tiny series, which extends the concepts of the M16C family to devices with low pin counts and small packages. The mainstay of this series ― the chips in M16C/28 group ― have been enhanced with motor control functions from higher-end models in the M16C family, as well as from devices in other Renesas Tiny-series product lines.

Home appliances encompass a huge market covering an extremely diverse range of product categories generally powered by fractional-horsepower or low-horsepower electric motors. Moreover, the product ranges within each category are further divided into variants extending from low-end to high-end models. Even if the scope of the discussion is limited to traditional whiteware (white goods) products such as air conditioners, refrigerators, dishwashers, washing machines, and clothes dryers that require electric motor control solutions, there are many, many product variations. Because of this diversity, the design requirements for motor control are extremely varied. However, the goals of quiet operation and energy efficiency are essentially universal.

For example, inverter control has become a standard feature in refrigerators for the Japanese domestic market. The operation of the compressor motor is controlled based on data from a number of temperature, door open/close, and other sensors. Two trends in home appliances are evident. Motors are becoming smaller and yet are just as powerful, and inverter control has become a standard technique for making the mechanisms operate more quietly. In particular, inverter control has become a necessity in washing machines because it allows continuously variable motor speeds and can quickly stop the motion of the washing tub when the door is opened.

Despite the many different home appliance models, Renesas offers microcomputers in the M16C family with performance points and feature sets that cover most motor control requirements for home appliances, despite the many different models. For refrigerators and washing machines, from low-end through to high-end products, there are numerous microcomputers that provide an integrated three-phase PWM output (see Figure 2). The economical single-chip solutions in the 16-bit M16C/Tiny series are among the most popular choices for new appliance designs. They have a high-performance M16C CPU core and internal flash memory. To save space and reduce cost, they use small packages with low pin counts.

Five basic concepts underpin the M16C/Tiny product line:
・The microcomputers inherit key characteristics from the M16C family, such as excellent noise immunity, low power consumption, and functions to prevent improper operation.
・The devices' CPU, peripheral functions, and pin layouts have a high degree of compatibility with other M16C family models for system design flexibility.
・The devices implement the Renesas "Tiny" series design concepts, which include a 16-bit internal bus with a wide range of peripheral functions, low pin-count packages (42 and 80 pins), 24Kbytes to 128Kbytes (+4Kbytes) of ROM, 1Kbytes to 12Kbytes of RAM, and 20MHz operation.
・They provide high-performance, highly reliable internal flash memory to enable code downloads in production and program updates in the field.
・The M16C/Tiny microcomputers aim at primary markets such as whiteware (inverter control), general industrial applications, PC peripherals, and portable devices.

Perspective on the product groups in the M16C/Tiny series can be gained by understanding how the series evolved. The M16C/26 group was the first product group to be developed. It was followed by the M16C/26A, M16C/28, and M16C/29 groups. Renesas now offers motor control solutions for home appliances based on all of these various product groups, and we are developing new ones, with a particular emphasis on the microcomputers in the M16C/28 group.

The microcomputers in the M16C/26 group inherited a number of features from the models M16C/62P group in the M16C family. Those features included a reset function, oscillation-halt detection circuit, and a watchdog timer (WDT) function that operates from a system clock or an on-chip oscillator that does not halt. Additionally, the chips have design features that help ensure safe system operation: hardware reset selection for monitoring timer, divide-by-eight selection for recovery from clock halt, etc. They have a flash erase-suspend function and provide (as an option) a small flash memory block for data storage (Data Flash) that can eliminate the need for external EEPROM. The devices operate at speeds up to 20MHz at 5V and come in a 48-pin package with a 7-millimeter-square mounting footprint.

To implement three-phase PWM motor control in home appliances, the members of the M16C/26 group have on-chip timers inherited from the M16C/62A or M16C/62N product groups. The instruction set and peripheral functions are compatible between these microcomputers, facilitating the porting of application code.

The next group of M16C/Tiny microcomputers that was introduced, the M16C/26A group, is based on the models in the M16C/26 group. However, they offer extra functionality: a frequency modification function for the on-chip oscillator, a circuit to start the on-chip oscillator after a reset, and a digital de-bounce function. The microcomputers in the M16C/26A group also have additional functions that enable a range of different motor control applications. Specifically, they provide an A/D converter function with delayed trigger, a position-data protection function that is synchronized with the three-phase motor waveform, a three-phase motor waveform output, and ports that are selectable with software.

The flagship M16C/28 product group offers all of the functions and performance features of the M16C/26 and M16C/26A groups, plus a few more (see Figure 1). These include input-capture and output-compare compare functions that allow more flexible signal control, and multi-master I2C bus functions for implementations containing with multiple subsystems.

The microcomputers in the M16C/29 group are another level up from the devices in the M16C/28 group. They add a single CAN 2.0B communication/networking function to the feature set of the M16C/28 group, with which they are upwardly compatible.

Home appliances that have particularly high performance requirements typically use multiple microcomputers. Many refrigerators, for example, use one microcomputer for system control based on multiple sensors and a second device for motor control. Similarly, many washing machines allocate a microcomputer for the control panel and a separate one for controlling the AC motor. Renesas is now proposing that various system control functions be integrated into the motor control microcomputer.

In the future, new members of the M16C/Tiny series of microcomputers will continue to be introduced for use in inverter and motor control applications in home appliances. Devices being planned will boost development efficiency and decrease system cost by offering the potential for total appliance control solutions in which spare processing power can be used for handling real-time control tasks.