Datasheet

TMC220X, TMC222X DATASHEET (Rev. 1.02 / 2017-MAY-16) 37
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6 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. With the enhanced stealthChop2, the driver automatically adapts
to the application for best performance. No more configurations are required. Optional configuration
allows for tuning the setting in special cases, or for storing initial values for the automatic adaptation
algorithm. For high velocity drives spreadCycle should be considered in combination with stealthChop.
Figure 6.1 Motor coil sine wave current with stealthChop (measured with current probe)
6.1 Automatic Tuning
stealthChop2 integrates an automatic tuning procedure (AT), which adapts the most important
operating parameters to the motor automatically. This way, stealthChop2 allows high motor dynamics
and supports powering down the motor to very low currents. Just two steps have to be respected by
the motion controller for best results: Start with the motor in standstill, but powered with nominal
run current (AT#1). Move the motor at a medium velocity, e.g. as part of a homing procedure (AT#2).
Figure 6.2 shows the tuning procedure.
Border conditions in for AT#1 and AT#2 are shown in the following table:
AUTOMATIC TUNING TIMING AND BORDER CONDITIONS
Step
Parameter
Conditions
Duration
AT#1
PWM_
OFS_AUTO
- Motor in standstill and actual current scale (CS) is
identical to run current (IRUN).
- If standstill reduction is enabled (pin PDN_UART=0),
an initial step pulse switches the drive back to run
current.
- Pins VS and VREF at operating level.
≤ 2^20+2*2^18 t
CLK
,
≤ 130ms
(with internal clock)
AT#2
PWM_
GRAD_AUTO
- Motor must move at a velocity, where a significant
amount of back EMF is generated and where the full
run current can be reached. Conditions:
- 1.5 * PWM_OFS_AUTO < PWM_SCALE_SUM <
4 * PWM_OFS_AUTO
- PWM_SCALE_SUM < 255.
Hint: A typical range is 60-300 RPM. Determine best
conditions with the evaluation board.
8 fullsteps are required
for a change of +/-1.
For a typical motor with
PWM_GRAD_AUTO
optimum at 64 or less, up
to 400 fullsteps are
required when starting
from OTP default 14.