December 2013

DocID18343 Rev 2

1/22

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

(see Appendix A: Reference document).

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