MC3PHAC Monolithic Intelligent Motor Controller, Rev. 2

8

Freescale Semiconductor

Introduction

Introduction

The MC3PHAC is a high-performance intelligent controller designed specifically to meet the requirements

for low-cost, variable-speed, 3-phase ac motor control systems. The device is adaptable and

configurable, based on its environment. Constructed with high-speed CMOS (complementary metal-

oxide semiconductor) technology, the MC3PHAC offers a high degree of performance and ruggedness

in the hostile environments often found in motor control systems.

The device consists of:

•

6-output pulse-width modulator (PWM)

•

4-channel analog-to-digital converter (ADC)

•

Phase-lock loop (PLL) based system oscillator

•

Low-power supply voltage detection circuit

•

Serial communications interface (SCI)

The serial communications interface is used in a mode, called PC master software mode, whereby control

of the MC3PHAC is from a host or master personal computer executing PC master software or a

microcontroller emulating PC master software commands. In either case, control via the internet is

feasible.

Included in the MC3PHAC are protective features consisting of dc bus monitoring and a system fault input

that will immediately disable the PWM module upon detection of a system fault.

Included motor control features include:

•

Open loop volts/Hertz speed control

•

Forward or reverse rotation

•

Start/stop motion

•

System fault input

•

Low-speed voltage boost

•

Internal power-on reset (POR)

Features

3-Phase Waveform Generation — The MC3PHAC generates six PWM signals which have been

modulated with variable voltage and variable frequency information in order to control a 3-phase ac motor.

A third harmonic signal has been superimposed on top of the fundamental motor frequency to achieve full

bus voltage utilization. This results in a 15 percent increase in maximum output amplitude compared to

pure sine wave modulation.

The waveform is updated at a 5.3 kHz rate (except when the PWM frequency is 15.9 kHz), resulting in

near continuous waveform quality. At 15.9 kHz, the waveform is updated at 4.0 kHz.

DSP Filtering — A 24-bit IIR digital filter is used on the SPEED input signal in standalone mode, resulting

in enhanced speed stability in noisy environments. The sampling period of the filter is 3 ms (except when

the PWM frequency is 15.9 kHz) and it mimics the response of a single pole analog filter having a pole at

0.4 Hz. At a PWM frequency of 15.9 kHz, the sampling period is 4 ms and the pole is located at 0.3 Hz.