Part 3 ― Motor Control Solutions for Key Application Sectors

Consumer Equipment ― Diverse Timer Functions that R8C/Tiny Microcomputers Provide Encourage Use of Brushless DC Motors

Motors provide the mechanical drive in many of the consumer devices that are considered essential in our daily lives. These motors must be low in cost, offer long-term durability, and run quietly. Recognizing that there is a growing trend toward the adoption of brushless DC motors, Renesas has incorporated into economical 16-bit R8C/Tiny microcomputers many different timer functions that are useful for controlling this type of motor. For example, models in the R8C/24 and R8C/25 groups include a timer RD unit and are supplied in a 52-pin package.

Electric motors are used in many of the consumer devices we use every day. Companies manufacturing these products strive to keep costs down and provide more efficient motor drive operation. Other engineering goals include quiet running and durability that ensures a long, maintenance-free operating life. These factors are combining to make brushless DC motors particularly desirable design choices in consumer equipment such as attic fans that must operate at low noise levels, providing efficient full-time ventilation at low cost. The fans also have to exhibit the maintenance-free operation expected of a semi-permanent fixture.

The number of different types of consumer equipment that are subject to similar requirements continues to grow year by year. Besides attic fans, products in which brushless DC motors are already becoming more common include electric screwdrivers, electric drills, ordinary room fans, electric wheelchairs, electrically operated beds, and the air movers used in the indoor units of air conditioners.

For motor control applications in such consumer products, Renesas offers its economical R8C/Tiny series of 16-bit microcomputers. These low-pin count devices (20 to 80 pins) with small-size packages are optimized for implementing brushless DC motor control at low cost. Despite their low pin count, they can implement long-term, stable motor control using the well-proven rectangular-wave drive technique. Thus, they allow customers to take advantage of the efficiency of brushless DC motors, while keeping product costs down.

R8C/Tiny microcomputers use the R8C CPU core and offer speeds up to 20MHz for strong processing performance. In fact, if an 80-pin class R8C/Tiny device is used to control the fan motor control in the indoor unit of an air conditioner, the chip typically has enough extra computing capacity to handle system control tasks, too.

Some models in this product line have up to 96Kbytes of on-chip flash memory and 7Kbytes of RAM. Their extensive range of built-in functions includes a multifunction timer, clock-synchronous or UART serial interface, input-capture timer, watchdog timer, oscillation-halt detection circuit, and noise canceller. A wide range of variations allows system engineers to make optimized design choices for diverse applications.

In the R8C/Tiny series, motor control applications for consumer equipment are covered by the R8C/2C, 2D, R8C/2A, 2B, R8C/24, 25, R8C/22, 23, R8C/20, 21, R8C/26, 27, and R8C/28, 29 groups (see Figure 2). The most popular choices are the microcomputers in the R8C/24 and R8C/25 groups (See Figure 1). The Photograph shows an interesting application for an R8C/24 device.

Of the on-chip peripheral functions offered for motor control applications by R8C/Tiny devices, the multifunction timer is particularly noteworthy. It encompasses six different timers with diverse capabilities: timers RA, RB, RC, RD, RE, and RF. All of these timers are carefully crafted for microcomputers with small numbers of pins.

Timers RC and RD can be used in PWM mode to generate a rectangular wave PWM output. Besides the PWM mode, which it shares with timer RD, timer RC provides a PWM mode 2 that can output pulses with any specified pulse width and with a specified delay relative to a trigger input.

Timer RD, on the other hand, offers a PWM mode 3 that can output a single-phase PWM waveform in which the forward and reverse phases do not overlap. Another mode available on timer RD is a complementary PWM mode where channels are combined to output a three-phase PWM waveform in which the forward and reverse phases do not overlap. Users can create a sinusoidal modulation in this mode to eliminate torque ripple. Timer RD also has a reset-synchronous PWM mode in which the forward and reverse phases are inverted and which also works by combining channels. The R8C/Tiny product groups that offer timer RD and timer RC functions are shown in the Table.

Timer RA can generate a three-phase output by using an interrupt to switch the I/O. However, timers RC or RD avoid the need for input pins. This is the reason that all R8C/Tiny versions, even the 20-pin ones, can be used to operate a brushless DC motor using a rectangular waveform (120-degree energization).

It should be noted here that the H8/Tiny series is another Renesas product line in the same class as the R8C/Tiny series and that those general-purpose devices are widely used for motor control. However, we recommend that customers switch to the R8C/Tiny series for new designs. Being newer-generation chips, the R8C/Tiny microcomputers support valuable functions such as power-on reset and can implement designs using fewer components. Transitions from H8/Tiny series solutions to R8C/Tiny series solutions are particularly smooth.

Renesas will continue to meet the evolving design requirements of consumer equipment that uses brushless DC motors by extending its range of motor control solutions with new R8C/Tiny models. One area of emphasis will be new microcomputers that offer increasingly high levels of cost-performance.