TMC603A Datasheet, PDF (24/44 Pages) TRINAMIC Motion Control GmbH & Co. KG. – Three phase motor driver with BLDC back EMF commutation hallFX™ and current sensing

TMC603A DATA SHEET (V. 1.15 / 2009-Nov-19)
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5.4.3 Block commutation chopper scheme for hallFX™
hallFX™ works perfectly with nearly every motor. You can use a standard block commutation scheme,
but the chopper must fulfill the following: The coils must be open for some percentage of the chopper
period, in order to allow the back-EMF of the motor to influence the coil voltages. The motor direction
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. You find the required commutation table in chapter 8.3.
H1
0V
Motor turning forward
Motor turning reverse
H2
0V
H3
0V
BH1
0V
BL1
0V
BH2
0V
BL2
0V
BH3
0V
BL3
0V
Hall
vector
3
1
5
4
6
2
Chopper on high side
(chopper events not shown)
Chopper on low side
figure 17: hallFX™ based commutation
5
1
3
2
6
4
Example: 50% chopper on
high and low side showing
3 chopper events
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.
Copyright © 2009 TRINAMIC Motion Control GmbH & Co. KG