TMC2100 DATASHEET (Rev. 1.07 / 2017-MAY-15)
17
during fastest applicable acceleration. Just as in the acceleration phase, during a deceleration phase
the voltage PWM amplitude must be adapted in order to keep the motor coil current constant.
Figure 5.2 Scope shot: current can follow on acceleration phase
Motor current
PWM scale
Velocity
PWM reaches
max. amplitude
255
RMS current
constant
P
W
M
Nominal current
(sine wave RMS)
_
G
R
k
A
o
D
D
A
o
Current may drop due
to high velocity
R
k
G
_
M
W
P
Stand still
PWM scale
0
0
Time
Current vs. velocity with acceleration in a good range
Figure 5.3 Current vs. velocity diagram
Be sure to use a symmetrical sense resistor layout and sense resistor traces of identical length and
well matching sense resistors for best performance.
The auto scaling function only starts up regulation during motor standstill. Do not start motion
directly after enabling stealthChop. Wait until the current regulation has reached a stable state before
starting a motion. Failure to do so will result in zero motor current!
In case the automatic scaling regulation is instable at your desired motion velocity, try modifying the
clock frequency. Also adapt the blank time (CFG5) and motor current for best result.
5.2.1 Lower Current Limit
The stealthChop current regulator imposes a lower limit for motor current regulation. As the coil
current can be measured in the shunt resistor during chopper on phase only, a minimum chopper
duty cycle allowing coil current regulation is given by the blank time as set by TBL and by the
chopper frequency. Therefore, the motor specific minimum coil current in stealthChop autoscaling
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