TMC5161 DATASHEET (Rev. 1.01 / 2018-NOV-20)
97
Parameter
Description
Range
Comment
vhighfs
&
vhighchm
These chopper configuration flags in CHOPCONF 0 / 1
need to be set for dcStep operation. As soon as
VDCMIN becomes exceeded, the chopper becomes
switched to fullstepping.
set to 1 for dcStep
TOFF
dcStep often benefits from an increased off time 2… 15
value in CHOPCONF. Settings >2 should be
preferred.
Settings 8…15 do not make
any difference to setting 8
for dcStep operation.
VDCMIN
This is the lower threshold for dcStep operation 0… 2^22 0: Disable dcStep
when using internal ramp generator. Below this
threshold, the motor operates in normal microstep
mode. In dcStep operation, the motor operates at
minimum VDCMIN, even when it is completely
blocked. Tune together with DC_TIME setting.
Set to the lower velocity
limit for dcStep operation.
Activation of stealthChop also disables dcStep.
DC_TIME
This setting controls the reference pulse width for 0… 1023 Lower limit for the setting
dcStep load measurement. It must be optimized
for robust operation with maximum motor torque.
A higher value allows higher torque and higher
velocity, a lower value allows operation down to
a lower velocity as set by VDCMIN.
is: tBLANK (as defined by
TBL) in clock cycles + n
with n in the range 1 to
100 (for a typical motor)
Check best setting under nominal operation
conditions, and re-check under extreme operating
conditions (e.g. lowest operation supply voltage,
highest motor temperature, and highest supply
voltage, lowest motor temperature).
DC_SG
This setting controls stall detection in dcStep 0… 255 Set slightly higher than
mode. Increase for higher sensitivity.
DC_TIME / 16
A stall can be used as an error condition by
issuing a hard stop for the motor. Enable sg_stop
flag for stopping the motor upon a stall event.
This way the motor will be stopped once it stalls.
17.5 Measuring Actual Motor Velocity in dcStep Operation
dcStep has the ability to reduce motor velocity in case the motor becomes slower than the target
velocity due to mechanical load. VACTUAL shows the ramp generator target velocity. It is not
influenced by dcStep. Measuring dcStep velocity is possible based on the position counter XACTUAL.
Therefore take two snapshots of the position counter with a known time difference:
ꢝ
ꢞ
ꢝ
ꢞ
ꢢꢎ퐶ꢘ푈ꢎꢒ ꢉ푖ꢍꢙꢀ − ꢢꢎ퐶ꢘ푈ꢎꢒ ꢉ푖ꢍꢙꢃ
ꢀ2ꢣ
푉ꢎ퐶ꢘ푈ꢎꢒꢡꢋꢓ푇ꢔꢊ
=
∗
ꢉ푖ꢍꢙꢀ − ꢉ푖ꢍꢙꢃ
푓
ꢋ퐿퐾
Example:
At 16.0 MHz clock frequency, a 0.954 second measurement delay would directly yield in the
velocity value, a 9.54 ms delay would yield in 1/100 of the actual dcStep velocity.
To grasp the time interval as precisely as possible, snapshot a timer each time the transmission of
XACTUAL from the IC starts or ends. The rising edge of NCS for SPI transmission provides the most
exact time reference.
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