The MC33033 is one of a series of high performance dc brushless motor controllers produced by Motorola. It contains all of the functions required to implement a limited–feature, open loop, three or four phase motor control system. Constructed with Bipolar Analog technology, it offers a high degree of performance and ruggedness in hostile industrial environments.The MC33033 contains a rotor position decoder for proper commutation sequencing, a temperature compensated reference capable of supplying sensor power, a frequency programmable sawtooth oscillator, a fully accessible error amplifier, a pulse width modulator comparator, three open collector top drive outputs, and three high current totem pole bottom driver outputs ideally suited for driving power MOSFETs.  Included in the MC33033 are protective features consisting of undervoltage lockout, cycle–by–cycle current limiting with a latched shutdown mode, and internal thermal shutdown. Typical motor control functions include open loop speed control, forward or reverse rotation, and run enable. In addition, the MC33033 has a 60°/120° select pin which configures the rotor position decoder for either 60° or 120° sensor electrical phasing inputs.

Three Phase Motor Commutation

The three phase application shown in Figure 1 is an open loop motor controller with full wave, six step drive. The upper power switch transistors are Darlington PNPs while the lower switches are N–Channel power MOSFETs. Each of these devices contains an internal parasitic catch diode that is used to return the stator inductive energy back to the power supply. The outputs are capable of driving a delta or wye connected stator, and a grounded neutral wye if split supplies are used. At any given rotor position, only one top and one bottom power switch (of different totem poles) is enabled. This configuration switches both ends of the stator winding from supply to ground which causes the current flow to be bidirectional or full wave. A leading edge spike is usually present on the current waveform and can cause  a current–limit error. The spike can be eliminated by adding an RC filter in series with the Current Sense Input. Using a low inductance type resistor for RS will also aid in spike reduction.

Figure 2 shows the commutation waveforms over two electrical cycles. The first cycle (0° to 360°) depicts motor operation at full speed while the second cycle (360° to 720°) shows a reduced speed with about 50% pulse width modulation. The current waveforms reflect a constant torque load and are shown synchronous to the commutation frequency for clarity.

Figure 1. MC33033 Three Phase, Six Step, Full Wave Motor Controller Circuit

Figure 2. MC33033 Three Phase, Six Step, Full Wave Commutation Waveforms

Figure 3 shows a three phase, three step, half wave motor controller. This configuration is ideally suited for automobile and other low voltage applications since there is only one power switch voltage drop in series with a given stator winding. Current flow is unidirectional or half wave because only one end of each winding is switched. The stator flyback voltage is clamped by a single zener and three diodes.

Figure 3. MC33033 Three Phase, Three Step, Half Wave Motor Controller Circuit

Three Phase Closed Loop Controller

The MC33033, by itself, is capable of open loop motor speed control. For closed loop speed control, the MC33033 requires an input voltage proportional to the motor speed. Traditionally this has been accomplished by means of a tachometer to generate the motor speed feedback voltage. Figure 4 shows an application whereby an MC33039 , powered from the 6.25 V reference (Pin 7) of the MC33033, is used to generate the required feedback voltage without the need of a costly tachometer. The same Hall sensor signals used by the MC33033 for rotor position decoding are utilized by the MC33039. Every positive or negative going  transition of the Hall sensor signals on any of the sensor lines causes the MC33039 to produce an output pulse of defined amplitude and time duration, as determined by the external resistor R₁ and capacitor C₁. The resulting output train of pulses present at Pin 5 of the MC33039 are integrated by the Error Amplifier of the MC33033 configured as an integrator, to produce a dc voltage level which is proportional to the motor speed. This speed proportional voltage establishes the PWM reference level at Pin 11 of the MC33033 motor controller and completes or closes the feedback loop. The MC33033 ouputs drive a TMOS power MOSFET 3–phase bridge. High current can be expected during conditions of start–up and when changing direction of the motor.

The system shown in Figure 4 is designed for a motor having 120/240 degrees Hall sensor electrical phasing. The system can easily be modified to accommodate 60/300 degree Hall sensor electrical phasing by removing the jumper (J1) at Pin 18 of the MC33033.

Figure 4. Closed Loop Brushless DC Motor Control Circuit With the MC33033 Using the MC33039

Sensor Phasing Comparison

There are four conventions used to establish the relative phasing of the sensor signals in three phase motors. With six step drive, an input signal change must occur every 60 electrical degrees, however, the relative signal phasing is dependent upon the mechanical sensor placement. A comparison of the conventions in electrical degrees is shown in Figure 5 . From the sensor phasing table (Figure 6 ), note that the order of input codes for 60° phasing is the reverse of 300°. This means the MC33033, when the 60°/120° select (Pin 18) and the FWD/REV (Pin 3) both in the high state (open), is configured to operate a 60° sensor phasing motor in the forward direction. Under the same conditions a 300° sensor phasing motor would operate equally well but in the reverse direction. One would simply have to reverse the FWD/REV switch (FWD/REV closed) in order to cause the 300° motor to also operate in the same direction. The same difference exists between the 120° and 240° conventions.

Figure 5. MC33033 Sensor Phasing Comparison

Figure 6. MC33033 Sensor Phasing Table

In this applications, the rotor position has always been given in electrical degrees since the mechanical position is a function of the number of rotating magnetic poles. The relationship between the electrical and mechanical position is: Electrical Degrees = Mechanical Degrees x (#Rotor Poles/2)

An increase in the number of magnetic poles causes more electrical revolutions for a given mechanical revolution. General purpose three phase motors typically contain a four pole rotor which yields two electrical revolutions for one mechanical.

Two and Four Phase Motor Commutation

The MC33033 configured for 60° sensor inputs is capable of providing a four step output that can be used to drive two or four phase motors. The truth table in Figure 7 shows that by connecting sensor inputs S_B and S_C together, it is possible to truncate the number of drive output states from six to four. The output power switches are connected to B_T, C_T, B_B, and C_B. Figure 8 shows a four phase, four step, full wave motor control application. Power switch transistors Q₁ through Q₈ are Darlington type, each with an internal parasitic catch diode. With four step drive, only two rotor position sensors spaced at 90 electrical degrees are required. The commutation waveforms are shown in Figure 9 .

Figure 10 shows a four phase, four step, half wave motor controller. It has the same features as the circuit in Figure 3 , except for the deletion of speed adjust.

Figure 7. MC33033 Two and Four Phase, Four Step, Commutation Truth Table

Figure 8. MC33033 Four Phase, Four Step, Full Wave Controller Circuit

Figure 9. MC33033 Four Phase, Four Step, Full Wave Commutation Waveforms

Figure 10. MC33033 Four Phase, Four Step, Half Wave Motor Controller Circuit

Brush Motor Control

Though the MC33033 was designed to control brushless dc motors, it may also be used to control dc brush–type motors. Figure 11 shows an application of the MC33033 driving a H–bridge affording minimal parts count to operate a brush–type motor. Key to the operation is the input sensor code [100] which produces a top–left (Q₁) and a bottom–right (Q₃) drive when the controller’s Forward/Reverse pin is at logic [1]; top–right (Q₄), bottom–left (Q₂) drive is realized when the Forward/Reverse pin is at logic [0]. This code supports the requirements necessary for H–bridge drive accomplishing both direction and speed control.

The controller functions in a normal manner with a pulse width modulated frequency of approximately 25 kHz. Motor speed is controlled by adjusting the voltage presented to the noninverting input of the Error Amplifier establishing the PWM's slice or reference level. Cycle–by–cycle current limiting of the motor current is accomplished by sensing the voltage (100 mV threshold) across the RS resistor to ground of the H–bridge motor current. The over current sense circuit makes it possible to reverse the direction of the motor, on the fly, using the normal Forward/Reverse switch, and not have to completely stop before reversing.

Figure 11. MC33033 H–Bridge Brush–Type Controller Circuit

LAYOUT CONSIDERATIONS

Do not attempt to construct any of the motor control circuits on wire–wrap or plug–in prototype boards. High frequency printed circuit layout techniques are imperative to prevent pulse jitter. This is usually caused by excessive noise pick–up imposed on the current sense or error amp inputs. The printed circuit layout should contain a ground plane with low current signal and high drive and output buffer grounds returning on separate paths back to the power supply input filter capacitor VM. Ceramic bypass capacitors (0.01 μF) connected close to the integrated circuit at V_CC, V_ref and error ampliflier noninverting input may be required depending upon circuit layout. This provides a low impedance path for filtering any high frequency noise. All high current loops should be kept as short as possible using heavy copper runs to minimize radiated EMI.