MC33039, NCV33039
Rotor Electrical Position (Degrees)
0
60
120
180
240
300
360
480
600
720
φ
A
60° Sensor
Electrical
Phasing
Input
φ
B
φ
C
φ
A
120° Sensor
Electrical
Phasing
Input
φ
B
φ
C
φ
A
Output
Latch
ISetI
Input
V
th
≈
0.67 V
CC
R
T
/C
T
f
out
Output
V
out
(AVG)
Constant Motor Speed
Increasing Motor
Speed
Figure 1. Typical Three Phase, Six Step Motor Application
OPERATING DESCRIPTION
The MC33039 provides an economical method of
implementing closed−loop speed control of brushless DC
motors by eliminating the need for a magnetic or optical
tachometer. Shown in the timing diagram of Figure 1, the
three inputs (Pins 1, 2, 3) monitor the brushless motor rotor
position sensors. Each sensor signal transition is digitally
detected, ORied at the Latch
iSeti
Input, and causes C
T
to
discharge. A corresponding output pulse is generated at f
out
(Pin 5) of a defined amplitude, and programmable width
determined by the values selected for R
T
and C
T
(Pin 6). The
average voltage of the output pulse train increases with
motor speed. When fed through a low pass filter or
integrator, a DC voltage proportional to speed is generated.
Figure 2 shows the proper connections for a typical closed
loop application using the MC33035 brushless motor
controller. Constant speed operation down to 100 RPM is
possible with economical three phase four pole motors.
The
φ
A
inverter output (Pin 4) is used in systems where the
controller and motor sensor phasing conventions are not
compatible. A method of converting from either convention
to the other is shown in Figure 3. For a more detailed
explanation of this subject, refer to the text above Figure 39
on the MC33035 data sheet.
The output pulse amplitude V
OH
is constant with
temperature and controlled by the supply voltage on V
CC
(Pin 8). Operation down to 5.5 V is guaranteed over
temperature. For systems without a regulated power supply,
an internal 8.25 V shunt regulator is provided.
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