BRUSHLESS DC MOTOR CONTROLLER
FSP33035
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 the figure in page 17. From the sensor phasing table, note that the order of input codes for 60° phasing is the
reverse of 300°. This means the FSP33035, when configured for 60° sensor electrical phasing, will operate a motor
with either 60° or 300° sensor electrical phasing, but resulting in opposite directions of rotation. The same is true for
the part when it is configured for 120° sensor electrical phasing; the motor will operate equally, but will result in
opposite directions of rotation for 120° for 240° conventions.
Sensor Phasing Comparison
Sensor Phasing Table
In this data sheet, the rotor position is always 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:
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 FSP33035 is also capable of providing a four step output that can be used to drive two or four phase motors.
The truth table in page 19 shows that by connecting sensor inputs SB and SC together, it is possible to truncate the
number of drive output states from six to four. The output power switches are connected to BT, CT, BB, and CB. The
figure in page 20 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 the figure
in page 21. Figure in page 22 shows a four phase, four step, half wave motor controller. It has the same features as
the circuit in the figure in page 16, except for the deletion of speed control and braking.
Two and Four Phase, Four Step, Commutation Truth Table
18/28
2007-3-16
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