Product specifications

R01AN0168ED0101 Rev. 01.01 24
Application Note
Chapter 5 Looking into the PWM and ZPD Tables
5.2.2 PWM Values
In the ideal case, one would expect that the values of the PWM duty cycles are
sine and cosine waveforms, if they are related to the microstep or the angle of
the motor anchor.
This assumes, that the force relations inside of the motor are ideal, that the
forces can be added and that the forces of the horizontal and vertical coils are
rectangular to each other. This is what is explained in the theory, as shown in
3.1 “The Physics of a Stepper Motor” on page 11
.
However, the mechanical physics of a stepper motor are not ideal, typically.
Therefore, the values of the PWM duty cycles along with the motor anchor
angle or microstep may showing waveforms like this:
Figure 5-4 Non-ideal PWM Settings of a typical Stepper Motor
In this figure, the value “1” of the PWM refers to a duty cycle of 100%, meaning
a value of “0x3FF” for the registers
CVPn or CHPn.
Even more, when changing the rotation direction or when running faster or
slower, the characteristics of a motor may vary. To support this, the ISM PWM
tables in low precision mode are supporting the rotation direction and one level
of speed hysteresis, which are changing the tables dynamically.
Note It is up to the user, to find out the best fitting PWM table sets of the used
motors. If no background data is available, it is recommended to start off with
ideal sine and cosine sequences for the PWM tables.
Left Turning
-1,5
-1
-0,5
0
0,5
1
1,5
0 163248648096112
Microstep
PWM %
Vertical PWM
Horizontal PWM