User Manual

AND8399/D
http://onsemi.com
12
155us
Latest noticeable step in
SLA voltage (SLA
voltage approx. 0V).
Figure 14. Define Maximum Operating Speed
The time measured between the rising edge of
the NXT signal (purple curve) and the latest
noticeable step in the SLA voltage (yellow
curve) will define the maximum operating
speed.
As can be seen in Figure 14 this time is about
155 ms.
Knowing that the stepping mode taken is 1/8
microstepping and that the coil current zero
crossing should at least take 155 ms, the
maximum NXT frequency is:
1
155 ms
+ 6450 Hz
(eq. 1)
This will result in a velocity of:
6450 Hz
8
+ 806
FS
sec
(eq. 2)
Figure 15 displays the result at 800 FS/sec
(close to the maximum speed). The measured
SLA voltage at this speed will still represent the
real BEMF (measured at the end of the zero
crossing).