This application note describes a software algorithm used for detecting an open-load condition. The algorithm refers to the L9935 two-phase stepper motor driver. The algorithm identifies the open-load failure within the failure class and filters out occurrences of false open-load failures.
The document details a specific software algorithm designed to detect open-load failures within the failure class of the L9935 bipolar stepper motor driver. The primary goal is to identify genuine faults while filtering out occurrences of false open-load detections caused by various operational factors.
Open-load checking occurs during flyback using fast decay, where the coil energy is fed back from ground to Vbat. A failure is flagged only if the voltage drop at Rshunt plus Ron does not reach a reference voltage for longer than 16 microseconds. The note explains that sporadic failures can increase due to decreasing motor current, increasing motor resistance or speed, resonance effects, and changes in current regulation mode.
A failure is flagged only if it lasts longer than 16 microseconds.
Open-load detection is performed during flyback using fast decay.