TMC5031 DATASHEET (Rev. 1.11 / 2016-APR-28)
40
7.4 chopSync2 for Quiet Motors
While a frequency adaptive chopper like spreadCycle provides excellent high velocity operation, in
some applications, a constant frequency chopper is preferred rather than a frequency adaptive
chopper. This may be due to chopper noise in motor standstill, or due to electro-magnetic emission.
chopSync provides a means to synchronize the choppers for both coils with a common clock, by
extending the off time of the coils. It integrates with both chopper principles. However, a careful set
up of the chopper is necessary, because chopSync2 can just increment the off times, but not reduce
the duration of the chopper cycles themselves. Therefore, it is necessary to test successful operation
best with an oscilloscope. Set up the chopper as detailed above, but take care to have chopper
frequency higher than the chopSync2 frequency. As high motor velocities take advantage of the
normal, adaptive chopper style, chopSync2 becomes automatically switched off using the VHIGH
velocity limit programmed within the motion controller.
A suitable chopSync2 SYNC value can be calculated as follows:
푓
ꢆ퐿퐾
푆푌푁퐶 = ⌊
⌋
64 ∗ 푓
ꢃꢏꢋꢆ
Example:
The motor is operated in spreadCycle mode (chm=0). The minimum chopper frequency for
standstill and slow motion (up to VHIGH) has been determined to be 25kHz under worst case
operation conditions (hot motor, low supply voltage). The standstill noise needs to be
minimized by using chopSync. The IC uses an external 16MHz clock.
Considering the chopper mode 0, SYNC has to be set for the closest value resulting in or
below the double frequency, e.g. 50kHz. Using above formula, a value of 5 results exactly and
can be used. Trying a value of 6, a frequency of 41.7kHz results, which still gives an effective
chopper frequency of slightly above 20kHz, and thus would also be a valid solution. A value
of 7 might still be good, but could already give high frequency noise.
In chopper mode 1, SYNC could be set to any value between 10 and 13 to be within the
chopper frequency range of 19.8kHz to 25kHz.
Parameter
Description
Setting Comment
SYNC
This register allows synchronization of the 0
chopper for both phases of a two phase motor in
order to avoid the occurrence of a beat, especially
at low motor velocities. It is automatically
switched off above VHIGH.
chopSync off
1…15
fCLK/64
…
fCLK/(15*64)
Hint: Set TOFF to a low value, so that the chopper
cycle is ended, before the next sync clock pulse
occurs. Set SYNC for the double desired chopper
frequency for chm=0, for the desired base chopper
frequency for chm=1.
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