User Manual

AND8399/D
http://onsemi.com
18
High Temperature
When operating the stepper motor driver at high
temperature it is possible that the SLA voltage drops
between two samples taken. This could create unwanted
results. For this reason it’s important to measure the SLA
voltage as fast as possible after it has been updated.
Next oscilloscope plot displays the problem.
Figure 19. Decrease of SLA−voltage at High Temperature
“Coil current
zero crossing”
Between two SLA measurements (= full step posi-
tions), the SLA voltage drops because of the high IC
temperature. Sampling the SLA voltage too late could
result in an incorrect Bemf voltage interpretation.
As can be seen, the SLA voltage drops between two full
step positions. If the SLA voltage is sampled too late by the
microcontroller or DSP, an incorrect Bemf voltage
interpretation will occur. If the SLA voltage is sampled right
after it has been updated, the temperature effect will have a
minimum influence on the result.
Good PCB design can reduce the drop of the
SLA−voltage. If a large enough PCB heat sink is foreseen or
an additional head sink is used to get the heat out of the
package, the die temperature will drop and the drop in
SLA−voltage will reduce.