AN3327 Datasheet, PDF (1/22 Pages) STMicroelectronics – L9942 back EMF stall detection algorithm

AN3327
Application note
L9942 back EMF stall detection algorithm
Introduction
The L9942 is an integrated stepper motor driver for bipolar stepper motors used primarily in
automotive head lamp leveling. The L9942 can easily be used for other stepper motor type
operations as well. Anything from adaptive head lamp leveling and HVAC blend door
actuator control to EGR valve and throttle control applications can take advantage of the
features found in the L9942.
In each of these applications, stall detection is desired to determine the extreme end of
travel positions or severe fault situations. This application note explains the advantages of
sensing Back Electro-Motive Force (back EMF or BEMF) as a method for determining rotor
or armature stall conditions. While this method can be used in all methods of driving a
stepper motor (full, half, and microstepping), the focus of this application note is on sensing
a stalled rotor during microstepping.
An overview and detailed discussion on the implementation of the L9942 (application
schematics and so on) can be found in the ST Microelectronics^® application note AN2650
(see Appendix A: Reference document).
December 2013
DocID18343 Rev 2
1/22
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