Datasheet

TMC2590 DATASHEET (V1.0 / 2019-FEB-22) 38
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Parameter
Description
Setting
Comment
TBL
Blanking time. This time needs to cover the
switching event and the duration of the ringing
on the sense resistor. For most low-current
applications, a setting of 16 or 24 is good. For
high-current applications, a setting of 36 or 54
may be required.
0
16 system clock cycles
1
24 system clock cycles
2
36 system clock cycles
3
54 system clock cycles
CHM
Chopper mode bit. SpreadCycle is recommended
for most applications.
0
SpreadCycle mode
1
Constant off time
mode
EN_PFD
Enable passive fast decay. Setting this bit, adds a
passive fast decay phase of 512 clock cycles for
each bridge following zero crossing of the motor
current. The passive fast decay will dampen the
energy of motor resonances at medium velocity.
1
Resonance dampening
on.
10.1 SpreadCycle Chopper
The SpreadCycle (patented) 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 10.3). 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 30%-70% of the chopper cycle in standstill and are important for low motor and driver
power dissipation.
Calculation of a starting value for the slow decay time TOFF:
EXAMPLE:
Target Chopper frequency: 25kHz.
Assumption: Two slow decay cycles make up for 50% of overall chopper cycle time











 
For the TOFF setting this means:
  󰇛

 

 󰇜
With 12 MHz clock this gives a setting of TOFF=3.0, i.e. 3.
With 16 MHz clock this gives a setting of TOFF=4.25, i.e. 4 or 5.
The hysteresis start 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 easiest to find the best setting by starting from a low hysteresis setting (e.g. HSTRT=0, HEND=0)
and increasing HSTRT, until the motor runs 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