TMC262 DATASHEET (Rev. 2.07 / 2013-FEB-14)
34
Parameter
TBL
CHM
Description
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.
Chopper mode bit
Setting
0
1
2
3
0
1
Comment
16 system
24 system
36 system
54 system
clock
clock
clock
clock
cycles
cycles
cycles
cycles
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:
where:
dI
COILBLANK
is the coil current change during the blanking time.
dI
COILSD
is the coil current change during the slow decay time.
t
SD
is the slow decay time.
t
BLANK
is the blanking time (as set by TBL).
V
M
is the motor supply voltage.
I
COIL
is the peak motor coil current at the maximum motor current setting CS.
R
COIL
and
L
COIL
are motor coil inductance and motor coil resistance.
With this, a lower limit for the start hysteresis setting can be determined:
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:
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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