Datasheet

TMC2590 DATASHEET (V1.0 / 2019-FEB-22) 41
www.trinamic.com
EXAMPLE:
A hysteresis of 4 has been chosen. You might decide to not use hysteresis decrement. In this case
set:
HEND=6 (sets an effective end value of 6-3=3)
HSTRT=0 (sets minimum hysteresis, i.e. 1: 3+1=4)
In order to take advantage of the variable hysteresis, we can set most of the value to the HSTRT, i.e.
4, and the remaining 1 to hysteresis end. The resulting configuration register values are as follows:
HEND=0 (sets an effective end value of -3)
HSTRT=6 (sets an effective start value of hysteresis end +7: 7-3=4)
Hint
Highest motor velocities benefit from setting TOFF to 2 or 3 and a short TBL of 2 or 1.
10.2 Classic Constant Off-Time Chopper
The classic constant off-time chopper uses a fixed-time fast decay following each on phase. While the
duration of the on phase is determined by the chopper comparator, the fast decay time needs to be
fast enough for the driver to follow the falling slope of the sine wave, but it should not be so long
that it causes excess motor current ripple and power dissipation. This can be tuned using an
oscilloscope or evaluating motor smoothness at different velocities. A good starting value is a fast
decay time setting similar to the slow decay time setting.
t
I
mean value = target current
target current + offset
on
sdfd
sdon
fd
Figure 10.4 Constant off-time chopper with offset showing the coil current during two cycles
After tuning the fast decay time, the offset should be tuned for a smooth zero crossing. This is
necessary because the fast decay phase makes the absolute value of the motor current lower than the
target current (see Figure 10.5). If the zero offset is too low, the motor stands still for a short
moment during current zero crossing. If it is set too high, it makes a larger microstep. Typically, a
positive offset setting is required for smoothest operation.