TMC2100 DATASHEET (Rev. 1.07 / 2017-MAY-15)
16
5 stealthChop™
stealthChop is an extremely quiet mode of operation for stepper motors. It is based on a
voltage mode PWM. In case of standstill and at low velocities, the motor is absolutely
noiseless. Thus, stealthChop operated stepper motor applications are very suitable for
indoor or home use. The motor operates absolutely free of vibration at low velocities.
With stealthChop, the motor current is applied by driving a certain effective voltage into
the coil, using a voltage mode PWM. There are no more configurations required except for the
regulation of the PWM voltage to yield the motor target current. Consider spreadCycle for high
velocity drives.
Figure 5.1 Motor coil sine wave current with stealthChop (measured with current probe)
5.1 Current Regulation
In order to match the motor current to a certain level, the voltage mode PWM voltage must be scaled
depending on the actual motor velocity. Several additional factors influence the required voltage level
to drive the motor at the target current: the motor resistance, its back EMF (i.e. directly proportional to
its velocity) as well as actual level of the supply voltage. For the ease of use, the TMC2100 uses an
automatic mode for current regulation which considers current feedback. The PWM frequency is
internally divided from the clock frequency.
A higher PWM frequency leads to increased dynamic power dissipation, but it may bring a benefit for
higher motor velocity.
PWM FREQUENCY FOR STEALTHCHOP
Clock frequency fCLK
18MHz
fPWM=2/683 fCLK
52.7kHz
16MHz
46.8kHz
(internal)
38kHz
12MHz
35.1kHz
10MHz
29.3kHz
8MHz
23.4kHz
Table 5.1 PWM frequency – green: recommended
5.2 Automatic Scaling
In stealthChop voltage PWM mode, the internal autoscaling function regulates the motor current to
the desired current setting. The driver measures the motor current during the chopper on time and
uses a proportional regulator in order match the motor current to the target current. The quality of
the regulation can be examined when monitoring the motor coil current at different velocities and
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