Though the MC33033 was designed to control brushless dc
motors, it may also be used to control dc brush−type motors.
Figure 45 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 th