TLE4943C datasheet(39/48 Pages) INFINEON

39 / 48 page

TLE4943C

Data Sheet

V 1.2, July 2018

3.7

Change of Direction of Encoder

A local extremum (maximum or minimum) of the magnetic input signal can be caused during a reversal of rotation

direction. In this case the local extremum can be detected by the IC and used for offset calibration. (E.g. the local

maximum marked by an arrow in the diagram below.) Obviously the calculated offset value will be incorrect with

respect to the following signal. As worst case a duty cycle up to max. 15% to 85% could occur for a few pulses.

After a re-calibration, which typically takes place after 2...3 zero-crossings the offset will be correct again and

hence the duty cycle. A local extremum is detected when the extremum exceeds the value of half of the difference

between the two previous extreme (dB > 0.25*dBpp). Smaller extrema are not deteced. As a result of "bad" duty

cycle after fast direction reversal the sampling points for direction detection are at unusual signal phase angles

also.

At a change of rotation direction in calibrated mode two consecutive samples of dBdir have the same sign therefore

direction detection is set to invalid. To guarantee a valid direction the next zero crossings after change of direction

are used to detect direction. The direction information validity at those two speed pulses is set to invalid and

direction of rotation is set to default. Also, the validity of signal amplitude measurement is set to invalid, signal

amplitude contains default values and LR is set to 0 (no error). At the latest with the third pulse after direction

reversal, direction information is valid and direction is issued again. Signal amplitude validity is set to valid and its

according signal amplitude measurement and LR is issued after two new valid extrema are found.

TLE4943C Datasheet(PDF) 39 Page - Infineon Technologies AG