TMC2225 DATASHEET (Rev. 1.15 / 2023-FEB-16)
57
11.4 Index Output
An active INDEX output signals that the sine curve of motor coil B is at its positive zero transition.
This correlates to the zero point of the microstep sequence. Usually, the cosine curve of coil A is at its
maximum at the same time. Thus, the index signal is active once within each electrical period and
corresponds to a defined position of the motor within a sequence of four fullsteps. The INDEX output
this way allows the detection of a certain microstep pattern, and thus helps to detect a position with
more precision than a stop switch can do.
Microstep
wave
COIL A
(CUR_A)
COIL B
(CUR_B)
0
Time
INDEX
OUT PU T
Time
STEP
PULSE
Time
Figure 11.3 Index signal at positive zero transition of the coil B sine curve
Hint
The index output allows precise detection of the microstep position within one electrical wave, i.e.,
within a range of four fullsteps. With this, homing accuracy and reproducibility can be enhanced to
microstep accuracy, even when using an inexpensive home switch.
Hint
In StealthChop at high velocity, the current waves will appear shifted against the index pulse, due to
the motor current lagging the voltage driven into the coil.
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