TMC262 DATASHEET (Rev. 2.07 / 2013-FEB-14)
35
An Excel spreadsheet is provided for performing these calculations.
As experiments show, the setting is quite independent of the motor, because higher current motors
typically also have a lower coil resistance. Choosing a medium default value for the hysteresis (for
example, effective HSTRT+HEND=10) normally fits most applications. The setting can be optimized by
experimenting with the motor: A too low setting will result in reduced microstep accuracy, while a
too high setting will lead to more chopper noise and motor power dissipation. When measuring the
sense resistor voltage in motor standstill at a medium coil current with an oscilloscope, a too low
setting shows a fast decay phase not longer than the blanking time. When the fast decay time
becomes slightly longer than the blanking time, the setting is optimum. You can reduce the off-time
setting, if this is hard to reach.
The hysteresis principle could in some cases lead to the chopper frequency becoming too low, for
example when the coil resistance is high compared to the supply voltage. This is avoided by splitting
the hysteresis setting into a start setting (HSTRT+HEND) and an end setting (HEND). An automatic
hysteresis decrementer (HDEC) interpolates between these settings, by decrementing the hysteresis
value stepwise each 16, 32, 48, or 64 system clock cycles. At the beginning of each chopper cycle, the
hysteresis begins with a value which is the sum of the start and the end values (HSTRT+HEND), and
decrements during the cycle, until either the chopper cycle ends or the hysteresis end value (HEND) is
reached. This way, the chopper frequency is stabilized at high amplitudes and low supply voltage
situations, if the frequency gets too low. This avoids the frequency reaching the audible range.
I
H
D
E
C
target current + hysteresis start
target current + hysteresis end
target current
target current - hysteresis end
target current - hysteresis start
on
sd
fd
sd
t
Figure 9.2 spreadCycle chopper mode showing the coil current during a chopper cycle
Three parameters control spreadCycle mode:
Parameter
Description
Setting
Comment
HSTRT
Hysteresis start setting. Please remark, that this 0… 7
value is an offset to the hysteresis end value
HEND.
This setting adds to
HEND.
%000: 1 %100: 5
%001: 2 %101: 6
%010: 3 %110: 7
%011: 4 %111: 8
Negative HEND: -3… -1
%0000: -3
HEND
Hysteresis end setting. Sets the hysteresis end 0… 2
value after a number of decrements. Decrement
interval time is controlled by HDEC. The sum
HSTRT+HEND must be <16. At a current setting CS
%0001: -2
%0010: -1
of max. 30 (amplitude reduced to 240), the sum
3
Zero HEND: 0
is not limited.
%0011: 0
4… 15
Positive HEND: 1… 12
%0100: 1 %1010: 7
%0101: 2 %1011: 8
%0110: 3 %1100: 9
%0111: 4 %1101: 10
%1000: 5 %1110: 11
%1001: 6 %1111: 12
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