Datasheet

TMC5041 DATASHEET (Rev. 1.13 / 2017-MAY-16) 43
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7.4 Combining stealthChop with other Chopper Modes
The TMC5041 allows combining stealthChop and different chopper modes based on velocity
thresholds. This way, the optimum chopper principle can be chosen for different velocity ranges. As a
first step, both chopper principles should be parameterized and optimized individually. In a next step,
a transfer velocity has to be fixed. For example, stealthChop operation is used for precise low speed
positioning, while spreadCycle shall be used for highly dynamic motion. VCOOLTHRS determines the
transition velocity. Use a low transfer velocity to avoid a jerk at the switching point. A jerk occurs
when switching at higher velocities, because the back-EMF of the motor (which rises with the
velocity) causes a phase shift of up to 90° between motor voltage and motor current. So when
switching at higher velocities between voltage PWM and current PWM mode, this jerk will occur with
increased intensity. At low velocities (e.g. 1 to a few 10 RPM), it can be completely neglected for most
motors. Therefore, the VCOOLTHRS should be set to a low velocity, in order to eliminate any jerk in
case an automatic switching between two chopper modes is desired. Set VCOOLTHRS and VHIGH to
high values (above VMAX) if you want to work with stealthChop only.
When enabling the stealthChop mode the first time using automatic current regulation, the motor
must be at stand still in order to allow a proper current regulation. When the drive switches to a
different chopper mode at a higher velocity, stealthChop logic stores the last current regulation
setting until the motor returns to a lower velocity again. This way, the regulation has a known
starting point when returning to a lower velocity, where stealthChop becomes re-enabled. Therefore,
neither the velocity threshold nor the supply voltage must be considerably changed during the phase
while the chopper is switched to a different mode, because otherwise the motor might lose steps or
the instantaneous current might be too high or too low.
A motor stall or a sudden change in the motor velocity may lead to the driver detecting a short
circuit or to a state of automatic current regulation, from which it cannot recover. Clear the error flags
and restart the motor from zero velocity to recover from this situation.
Hint
Start the motor from standstill when switching on stealthChop the first time and keep it stopped for
at least 128 chopper periods to allow stealthChop to do initial standstill current control.