User Manual

AND8399/D
http://onsemi.com
9
When working in ‘transparent’ mode, the SLA voltage
will be updated at the rate of the PWM frequency when the
motor is located in the “coil current zero crossing”. The
transient behavior can be monitored.
As can be seen in Figure 12, the transient behavior has
ended before the next (micro)step is set. The real Bemf
voltage of the stepper motor can be measured.
Verifying the transient behavior of the coil voltage during
the current less state is only done during development (for
most applications). In the final application it’s not needed to
sample this complete transient behavior. For this
AMIS−305xx has a so called ‘not transparent’ mode.
In this mode the coil voltage is also sampled at the PWM
rate when the coil current is zero but the voltage on the
SLA−pin is only updated from the moment the “coil current
zero crossing” state is left (see also Figure 12). The transient
behavior will not be seen by the microcontroller (which is
also not needed for most applications).
Keep in mind that the SLA voltage is only updated when
leaving the current less state. The SLA voltage measured
during the current less state will actually represent the Bemf
voltage of the previous full step.