Out in Front: September 12, 1996

Washing machines are undergoing a revolution. You can now use TI's TMS320C240 DSP to control a variable-speed, direct-drive, inexpensive brushless motor, eliminating or reducing the belts, gears, and sensors that have typically been required in these home appliances. The C240, the first DSP optimized for motor-control applications, not only benefits washing machines, but also countless other motor-control applications.

Traditional designs contain brush-type motors and basic electronics, but most new designs are using brushless motors. With the more reliable and efficient brushless motors, you must use a processor to commutate the motor; this is where the math-crunching capability of a DSP comes in handy.

The C240 uses TI's 16-bit, fixed-point, T320C2xLP DSP core to handle a motor's math-related control functions. The core is code-compatible with the TMS320C1x, C2x, C2xx, and C5x families, allowing you to reuse code and development tools from previous designs. The C240 supports motor commutation, command generation, control-algorithm processing, data communications, and system-monitoring functions. Command generation tells the motor how fast to go and how to get where it's going. One of the control algorithms determines the digital position and velocity loop and allows you to avoid the use of a tachometer to derive the motor's velocity. The control algorithms also reduce motor noise by improving torque ripple. The DSP also calculates a power-factor correction that performs the necessary phase shifts to synchronize the current and voltage coming from the power line.

In addition to the DSP core, the C240 integrates a motor-control event manager that supports up to 12 PWM outputs, three timers, nine comparators, dead-band generation logic, a state-space vector PWM generator, and four capture inputs (two of which can serve as direct inputs for optical-encoder quadrature pulses). The dead-band- generation logic performs the calculations to delay the switching of power transistors. The state-space vector PWM generator in-creases the life of power transistors by using space-vector mathematics to determine which transistors to turn on and how hard to turn them on.

The DSP controller also includes two serial interfaces, 32 bits of digital I/O, a watchdog timer, and a low-voltage detector. The C240 contains two 10-bit AD converters, which are used by three-phase motors that must sample at least two phases simultaneously. TI will offer a version of the 240, the F240, that contains 16k words of flash memory. The C240 costs $10 (100,000). The flash version, available in the first quarter of 1997, will be slightly more expensive.

—by Markus Levy

Texas Instruments Inc, Denver, CO. (800) 477-8924, ext 4500, http://www.ti.com.