TMC5160 DATASHEET (Rev. 1.08 / 2018-NOV-19)
64
Chopper mode
stealthChop
spreadCycle
option
option
v
TSTEP < TPWMTHRS*16/16
TSTEP > TPWMTHRS
0
t
current
I_RUN
I_HOLD
VACTUAL
~1/TSTEP
RMS current
TRINAMIC, B. Dwersteg, 14.3.14
Figure 7.7 TPWMTHRS for optional switching to spreadCycle
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. TPWMTHRS determines
the transition velocity. Read out TSTEP when moving at the desired velocity and program the
resulting value to TPWMTHRS. 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. A high jerk may even produce a temporary overcurrent condition (depending
on the motor coil resistance). At low velocities (e.g. 1 to a few 10 RPM), it can be completely
neglected for most motors. Therefore, consider the switching jerk when choosing TPWMTHRS. Set
TPWMTHRS zero 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
stealthChop 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.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
