Datasheet

TMC2209 DATASHEET (Rev. 1.03 / 2019-JUN-26) 62
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13.3 MicroPlyer Step Interpolator and Stand Still Detection
For each active edge on STEP, MicroPlyer produces microsteps at 256x resolution, as shown in Figure
13.2. It interpolates the time in between of two step impulses at the step input based on the last
step interval. This way, from 2 microsteps (128 microstep to 256 microstep interpolation) up to 256
microsteps (full step input to 256 microsteps) are driven for a single step pulse.
The step rate for the interpolated 2 to 256 microsteps is determined by measuring the time interval of
the previous step period and dividing it into up to 256 equal parts. The maximum time between two
microsteps corresponds to 2
20
(roughly one million system clock cycles), for an even distribution of
256 microsteps. At 12 MHz system clock frequency, this results in a minimum step input frequency of
roughly 12 Hz for MicroPlyer operation. A lower step rate causes a standstill event to be detected. At
that frequency, microsteps occur at a rate of (system clock frequency)/2
16
~ 256 Hz. When a stand still
is detected, the driver automatically begins standby current reduction if selected by pin PDN.
Attention
MicroPlyer only works perfectly with a jitter-free STEP frequency.
STEP
Interpolated
microstep
Active edge (dedge=0) Active edge (dedge=0) Active edge (dedge=0)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 32
Active edge (dedge=0)
STANDSTILL
(stst) active
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
Motor
angle
52 53 54 55 56 57 58 59 60 61 62 63 64 65 6651
2^20 t
CLK
Figure 13.2 MicroPlyer microstep interpolation with rising STEP frequency (Example: 16 to 256)
In Figure 13.2, the first STEP cycle is long enough to set the stst bit standstill. Detection of standstill
will enable the standby current reduction. This bit is cleared on the next STEP active edge. Then, the
external STEP frequency increases. After one cycle at the higher rate MicroPlyer adapts the interpolated
microstep rate to the higher frequency. During the last cycle at the slower rate, MicroPlyer did not
generate all 16 microsteps, so there is a small jump in motor angle between the first and second
cycles at the higher rate.