TMC262 DATASHEET (Rev. 2.07 / 2013-FEB-14)
34
Parameter
Description
Setting
Comment
TBL
Blanking time. This time needs to cover the 0
16 system clock cycles
24 system clock cycles
36 system clock cycles
54 system clock cycles
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.
1
2
3
CHM
Chopper mode bit
0
1
spreadCycle mode
Constant off time
mode
9.1 spreadCycle Mode
The spreadCycle chopper algorithm (pat.fil.) 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 9.2). The slow decay phases limit the maximum chopper
frequency and are important for low motor and driver power dissipation. The hysteresis start setting
limits the chopper frequency by forcing the driver to introduce a minimum amount of current ripple
into the motor coils. The motor inductance limits the ability of the chopper to follow a changing
motor current. The duration of the on phase and the fast decay phase must be longer than the
blanking time, because the current comparator is disabled during blanking. This requirement is
satisfied by choosing a positive value for the hysteresis as can be estimated by the following
calculation:
ꢀꢾꣃꢼꢶ꣄
ꢆꢪꣂꢷꣃꢾꣃꢼꢶ꣄ ꢌ ꢲꢬ ꢱ
ꣂꢷꣃ
ꢦ ꢱ ꢀꢭ꣎
ꢆꢪꣂꢷꣃꢭ꣎ ꢌ ꢴꣂꢷꣃ ꢱ ꢪꣂꢷꣃ
ꢱ
ꣂꢷꣃ
where:
dICOILBLANK is the coil current change during the blanking time.
dICOILSD is the coil current change during the slow decay time.
tSD is the slow decay time.
tBLANK is the blanking time (as set by TBL).
VM is the motor supply voltage.
ICOIL is the peak motor coil current at the maximum motor current setting CS.
RCOIL and LCOIL are motor coil inductance and motor coil resistance.
With this, a lower limit for the start hysteresis setting can be determined:
ꢦ ꢱ ꢦꢧꢿ ꢮꢒ ꢯ ꢐ
ꢏ
ꢔ
ꢱ
ꢨ꣏ ꢀꢉꢅꢉ ꣐ ꢇꢒꢀꢁꢅꢀ ꣑ ꢆꢪꣂꢷꣃꢾꣃꢼꢶ꣄ ꢯ ꢆꢪꣂꢷꣃꢭ꣎
ꢱ
ꢪꣂꢷꣃ
ꢰꢦ
Example:
For a 42mm stepper motor with 7.5mH, 4.5Ω phase, and 1A RMS current at CS=31, i.e. 1.41A
peak current, at 24V with a blank time of 1.5µs:
ꢦ꣒
ꢆꢪꣂꢷꣃꢾꣃꢼꢶ꣄ ꢌ ꢦꢧꢲ ꢱ
ꢌ ꣖꣔ꢧꢈ꣗
꣓꣔꣕ꢈꢨ
ꢦ ꢱ ꣕꣒
ꢆꢪꣂꢷꣃꢭ꣎ ꢌ ꢧ꣔꣕꣘ ꢱ ꢐ꣔ꢧꢐ꣗ ꢱ
ꢌ ꢿ꣔꣕ꢈ꣗
꣓꣔꣕ꢈꢨ
With this, the minimum hysteresis start setting is 5.2. A value in the range 6 to 10 can be
used.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
