TMC5031 DATASHEET (Rev. 1.11 / 2016-APR-28)
35
Three parameters are used for controlling both chopper modes:
Parameter
Description
Setting Comment
Sets the slow decay time (off time). This setting also
limits the maximum chopper frequency.
TOFF
0
chopper off
off time setting NCLK= 12 +
32*TOFF
(1 will work with minimum
blank time of 24 clocks)
16 tCLK
1…15
Setting this parameter to zero completely disables all
driver transistors and the motor can free-wheel.
Selects the comparator blank time. This time needs to
safely cover the switching event and the duration of the
ringing on the sense resistor. For most applications, a
setting of 1 or 2 is good. For highly capacitive loads, 2
e.g. when filter networks are used, a setting of 2 or 3
TBL
0
1
24 tCLK
36 tCLK
54 tCLK
3
will be required.
Selection of the chopper mode
chm
0
1
spreadCycle
classic const. off time
7.1 spreadCycle Chopper
The spreadCycle (pat.) chopper algorithm is a precise and simple to use chopper mode which
automatically determines the optimum length for the fast-decay phase. 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 7.3). 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:
Assumptions:
Target Chopper frequency: 25kHz
Two slow decay cycles make up for 50% of overall chopper cycle time
1
50
1
2
푡ꢇꢌꢌ
=
∗
∗
= 10µ푠
25푘퐻푧 100
For the TOFF setting this means:
푇푂퐹퐹 = ꢍ푡ꢇꢌꢌ ∗ 푓 − 12ꢎ/32
ꢆ퐿퐾
With 12 MHz clock this gives a setting of TOFF=3.4, i.e. 3 or 4.
With 16 MHz clock this gives a setting of TOFF=4.6, 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
resistor voltages (see Figure 7.2). 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.
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