TMC5031 DATASHEET (Rev. 1.11 / 2016-APR-28)
57
12 Sine-Wave Look-up Table
Each of the TMC5031 drivers provides a programmable look-up table for storing the microstep current
wave. As a default, the tables are pre-programmed with a sine wave, which is a good starting point
for most stepper motors. Reprogramming the table to a motor specific wave allows drastically
improved microstepping especially with low-cost motors.
12.1 User Benefits
Microstepping
Motor
Torque
–
–
–
extremely improved with low cost motors
runs smooth and quiet
reduced mechanical resonances yields improved torque
12.2 Microstep Table
In order to minimize required memory and the amount of data to be programmed, only a quarter of
the wave becomes stored. The internal microstep table maps the microstep wave from 0° to 90°. It
becomes symmetrically extended to 360°. When reading out the table the 10-bit microstep counter
MSCNT addresses the fully extended wave table. The table is stored in an incremental fashion, using
each one bit per entry. Therefore only 256 bits (ofs00 to ofs255) are required to store the quarter
wave. These bits are mapped to eight 32 bit registers. Each ofs bit controls the addition of an
inclination Wx or Wx+1 when advancing one step in the table. When Wx is 0, a 1 bit in the table at
the actual microstep position means “add one” when advancing to the next microstep. As the wave
can have a higher inclination than 1, the base inclinations Wx can be programmed to -1, 0, 1, or 2
using up to four flexible programmable segments within the quarter wave. This way even negative
inclination can be realized. The four inclination segments are controlled by the position registers X1
to X3. Inclination segment 0 goes from microstep position 0 to X1-1 and its base inclination is
controlled by W0, segment 1 goes from X1 to X2-1 with its base inclination controlled by W1, etc.
When modifying the wave, care must be taken to ensure a smooth and symmetrical zero transition
when the quarter wave becomes expanded to a full wave. The maximum resulting swing of the wave
should be adjusted to a range of -248 to 248, in order to give the best possible resolution while
leaving headroom for the hysteresis based chopper to add an offset.
y
256
248
START_SIN90_120
0
X1 X2 X3
255 256
START_SIN
512
768
0
MSCNT
LUT stores
entries 0 to 255
-248
Figure 12.1 LUT programming example
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
