TMC603 DATA SHEET (V. 1.06 / 26. Mar. 2009)
23
is determined by the start-up scheme, since the hallFX signals depend on the direction. Thus, the
same commutation scheme is used for turn right and turn left! Only a single commutation table is
required.
Motor turning forward
Motor turning reverse
0V
0V
0V
0V
0V
0V
0V
0V
0V
H1
H2
H3
BH1
BL1
BH2
BL2
BH3
BL3
Hall
vector
3
1
5
4
6
2
5
1
3
2
6
4
Chopper on high side
Chopper on low side
(chopper events not shown)
Example: 50% chopper on
high and low side showing
3 chopper events
figure 17: hallFX based commutation
A chopper scheme fulfilling the desired coil open time per chopper period is shown here: Both, the
high side driver and the low side driver are chopped with the same signal. The coil open time
automatically is inverted to the duty cycle. In a practical application, the motor can run with a duty
cycle of 15% to 25% (minimum motor velocity at low load) up to 90% to 95% (maximum motor
velocity). The exact values depend on the actual motor. With a lower duty cycle the motor would not
start, or back EMF would be too small to yield a valid hallFX signal. With a higher duty cycle, the back
EMF would not be visible at the coil voltages, because the coils would be connected to GND or VM
nearly the whole time. The minimum resulting coil open time thus is 5% to 10%. This simple chopper
scheme automatically gives a longer measuring time at low velocities, when back EMF is lower. The
actual borders for the commutation should be checked in the actual application. Provide enough
headroom to compensate for variations due to motor load, mechanics and production stray.
5.4.4 Start-up sequence for the motor with forced commutation
In order to start the motor running with hallFX, it must reach a minimum velocity. The microcontroller
needs to take care of this by starting the motor in a forward control mode, without feedback – just like
a stepper motor. In order to allow a smooth transition to feedback mode, the same chopper scheme
should be used as described above. Alternatively, the chopper scheme can be changed a few
electrical periods before you switch to hallFX. This allows for example to start-up the motor using a
sine commutation, to get a smooth movement also at low motor velocities. In a practical application,
only a few percent up to 10% of the maximum motor velocity are sufficient for hallFX operation.
Turn the motor up to a minimum velocity, where you safely get correct hallFX signals. Since rotation of
the motor can not be measured during this phase, the motor needs to be current controlled, with a
current which in every case is high enough to turn the mechanical load. Current control can be done
by feedback control, or by adapting the duty cycle to the motor characteristics. Further, the minimum
starting speed and acceleration needs to be set matching the application. For sample code, please
see www.trinamic.com. Upon reaching the threshold for hallFX operation, a valid hall signal becomes
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
