TMP88CS42NG Datasheet, PDF (132/216 Pages) Toshiba Semiconductor – 8 Bit Microcontroller

13. Motor Control Circuit (PMD: Programmable motor
driver)
TMP88CS42NG
13.1 Outline of Motor Control
The following explains the method for controlling a brushless DC motor with sine wave drive. In a brushless DC
motor, the rotor windings to which to apply electric current are determined from the rotor’s magnetic pole position,
and the current-applied windings are changed as the rotor turns. The rotor’s magnetic pole position is determined
using a sensor such as a hall IC or by detecting polarity change (zero-cross) points of the induced voltage that devel-
ops in the motor windings (sensorless control). For the sensorless case, the induced voltage is detected by applying
electric current to two phases and not applying electric current to the remaining other phase. In this two-phase cur-
rent on case, there are six current application patterns as shown in Table 13-1, which are changed synchronously
with the phases of the rotor. In this two-phase current on case, the current on time in each phase is 120 degrees rela-
tive to 180 degrees of the induced voltage.
Table 13-1 Current Application Patterns
Current
Application Pattern
Mode 0
Mode 1
Mode 2
Mode 3
Mode 4
Mode 5
Upper Transistor
u
v
w
ON
OFF
OFF
ON
OFF
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
OFF
ON
OFF
OFF
ON
Lower Transistor
x
y
z
OFF
ON
OFF
OFF
OFF
ON
OFF
OFF
ON
ON
OFF
OFF
ON
OFF
OFF
OFF
ON
OFF
Current on Winding
U→V
U→W
V→W
V→U
W→U
W→V
Note: One of the upper or lower transistors is PWM controlled.
For brushless DC motors, the number of revolutions is controlled by an applied voltage, and the voltage applica-
tion is controlled by PWM. At this time, the current on windings need to be changed in synchronism with the phases
of the voltage induced by revolutions. Control timing in cases where the current on windings are changed by means
of sensorless control is illustrated in Figure 13-4. For three-phase motors, zero-crossing occurs six times during one
cycle of the induced voltage (electrical angle 360 degrees), so that the electrical angle from one zero-cross point to
the next is 60 degrees. Assuming that this period comprises one mode, the rotor position can be divided into six
modes by zero-cross points. The six current application patterns shown above correspond one for one to these six
modes. The timing at which the current application patterns are changed (commutation) is out of phase by 30
degrees of electrical angle, with respect to the position detection by an induced voltage.
Mode time is obtained by detecting a zero-cross point at some timing and finding an elapsed time from the preced-
ing zero-cross point. Because mode time corresponds to 60 degrees of electrical angle, the following applies for the
case illustrated in Figure 13-4.
1. Current on windings changeover (commutation) timing
30 degrees of electrical angle = mode time/2
2. Position detection start timing 45 degrees of electrical angle = mode time × 3/4
3. Failure determination timing 120 degrees of electrical angle = mode time × 2
Timings are calculated in this way. The position detection start timing in 2 is needed to prevent erroneous detection
of the induced voltage for reasons that even after current application is turned off, the current continues flowing due
to the motor reactance.
Control is exercised by calculating the above timings successively for each of the zero-cross points detected six
times during 360 degrees of electrical angle and activating commutation, position detection start, and other opera-
tions according to that timing.
In this way, operations can be synchronized to the phases of the induced voltage of the motor.
The timing needed for motor control as in this example can be set freely as desired by using the internal timers of
the microcontroller’s PMD unit.
Also, sine wave control requires controlling the PWM duty cycle for each pulse. Control of PWM duty cycles is
accomplished by counting degrees of electrical angle and calculating the sine wave data and voltage data at the
counted degree of electrical angle.
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