TMC5160 DATASHEET (Rev. 1.08 / 2018-NOV-19)
Motor current
63
PWM scaling
(PWM_SCALE_SUM)
PWM reaches
max. amplitude
255
D
A
R
G
Constant motor
RMS current
_
M
W
P
Nominal current
(e.g. sine wave RMS)
PWM_OFS
0
0
VPWMMAX
Velocity
Figure 7.6 Velocity based PWM scaling (pwm_autoscale=0)
Hint
The values for PWM_OFS and PWM_GRAD can easily be optimized by tracing the motor current with a
current probe on the oscilloscope. Alternatively, automatic tuning determines these values and they
can be read out from PWM_OFS_AUTO and PWM_GRAD_AUTO.
UNDERSTANDING THE BACK EMF CONSTANT OF A MOTOR
The back EMF constant is the voltage a motor generates when turned with a certain velocity. Often
motor datasheets do not specify this value, as it can be deducted from motor torque and coil current
rating. Within SI units, the numeric value of the back EMF constant CBEMF has the same numeric value
as the numeric value of the torque constant. For example, a motor with a torque constant of 1 Nm/A
would have a CBEMF of 1V/rad/s. Turning such a motor with 1 rps (1 rps = 1 revolution per second =
6.28 rad/s) generates a back EMF voltage of 6.28V. Thus, the back EMF constant can be calculated as:
ꢚ
ꢜ
푉
퐻표푙푑푖푛푔ꢘ표푟푞푢ꢙ ꢛꢍ
퐶퐵ꢔ푀ꢕ
ꢖ
ꢗ =
푟푎푑/푠
ꢀ ∗ 퐼ꢋ푂ꢌ퐿푁푂푀ꢚꢎꢜ
ICOILNOM is the motor’s rated phase current for the specified holding torque
HoldingTorque is the motor specific holding torque, i.e. the torque reached at ICOILNOM on both coils.
The torque unit is [Nm] where 1Nm = 100Ncm = 1000mNm.
The voltage is valid as RMS voltage per coil, thus the nominal current is multiplied by 2 in this
formula, since the nominal current assumes a full step position, with two coils operating.
7.5 Combining stealthChop and spreadCycle
For applications requiring high velocity motion, spreadCycle may bring more stable operation in the
upper velocity range. To combine no-noise operation with highest dynamic performance, the TMC5160
allows combining stealthChop and spreadCycle based on a velocity threshold (Figure 7.7). With this,
stealthChop is only active at low velocities.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
