TMC2100 DATASHEET (Rev. 1.07 / 2017-MAY-15)
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6.1 spreadCycle Chopper
The patented spreadCycle chopper algorithm is a precise and simple to use chopper mode which
automatically determines the optimum length for the fast-decay phase. The spreadCycle will provide
superior microstepping quality even with default settings. Several parameters are available to
optimize the chopper to the application.
Each chopper cycle is comprised of an on phase, a slow decay phase, a fast decay phase and a
second slow decay phase (see Figure 6.3). The two slow decay phases and the two blank times per
chopper cycle put an upper limit to the chopper frequency. The slow decay phases typically make up
for about 50%-75% of the chopper cycle in standstill and are important for low motor and driver
power dissipation.
EXAMPLE
ꢄ
At 16MHz clock frequency a low tOFF setting (140 tCLK) sets ꢀ푂퐹퐹 = 140 ∗
= 8.75휇푠. Each chopper
ꢄꢅ푀퐻푧
cycle then uses 2 * 8.75µs = 17.2 µs of slow decay time.
The hysteresis setting forces the driver to introduce a minimum amount of current ripple into the
motor coils. The current ripple must be higher than the current ripple which is caused by resistive
losses in the motor in order to give best microstepping results. This will allow the chopper to
precisely regulate the current both for rising and for falling target current. The time required to
introduce the current ripple into the motor coil also reduces the chopper frequency. Therefore, a
higher hysteresis setting will lead to a lower chopper frequency. The motor inductance limits the
ability of the chopper to follow a changing motor current. Further the duration of the on phase and
the fast decay must be longer than the blanking time, because the current comparator is disabled
during blanking.
It is easy to find the best setting by starting with the lowest hysteresis setting (CFG4=GND). Use a
higher setting in case the motor does not run smoothly at low velocity settings. This can best be
checked when measuring the motor current either with a current probe or by probing the sense
resistor voltages (see Figure 6.2). Checking the sine wave shape near zero transition will show a small
ledge between both half waves in case the hysteresis setting is too small. At medium velocities (i.e.
100 to 400 fullsteps per second), a too low hysteresis setting will lead to increased humming and
vibration of the motor.
Figure 6.2 No ledges in current wave with sufficient hysteresis (magenta: current A, yellow &
blue: sense resistor voltages A and B)
A too high hysteresis setting will lead to reduced chopper frequency and increased chopper noise but
will not yield any benefit for the wave shape.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
