tle4942, tle4942c tle4942 - tle4942c data sheet february 2002 1 appendix b release 1.1 1. occurrence of initial calibration delay time t d,input if there is no input signal (standstill), a new initial calibration is triggered each 0.7s. this calibration has a duration t d,input of max. 300s. no input signal change is detected during that initial calibration time. in normal operation (signal startup) the probability of t d,input to come into effect is: t d,input / time frame for new calibration 300s/700ms = 0,05%. after ic resets (e.g. after a significant undervoltage) t d,input will always come into effect. 2. magnetic input signal extremely close to a pga switching threshold during signal startup: after signal startup normally all pga switching into the appropriate gain state happens within less than one signal period. this is included in the calculation for n dz-start . for the very rare case that the signal amplitude is extremely close to a pga switching threshold and the full range of the following speed adc respectively, a slight change of the signal amplitude can cause one further pga switching. it can be caused by non-perfect magnetic signal (amplitude modulation due to tolerances of pole-wheel, tooth wheel or air gap variation). this additional pga switching can result in a further delay of the output signal (n dz-start ) up to three magnetic edges leading to a worst case of n dz-start =9. due to the low probability of this case it is not defined as max. value in the data sheet. (for a more detailed explanation please refer to the document "tle4941/42 - frequently asked questions").
tle4942, tle4942c tle4942 - tle4942c data sheet february 2002 2 3. fast change of direction signal at small fields: the described behaviour can happen when rotation direction is changed in t < 0.7s direction change of input signal at t=690 -3 -2 -1 0 1 2 3 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 time / ms delta b a local extreme (maximum or minimum) of the magnetic input signal can be caused during a reversal of rotation direction. in this case the local extreme can be detected by the ic and used for offset calibration. (e.g. a local maximum marked by an arrow in the above diagram.) 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 also. 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 small magnetic input signals ( ? b < 1.7 * ? b warning ) this can lead to incorrect direction information. duration: max. 7 pulses, in very rare cases (additional pga transition during calibration similar to 2.) max. 9 pulses. a local extremum close to the zero-crossing theoretically could lead to distances down to 45s of two consecutive output pulses at the point of direction reversal as well as a b warning pulse also. 4. behaviour close to the magnetic thresholds b warning , b limit , (b el ) real non-perfect magnetic signals and intrinsic thermal noise cause amplitude variations. very close to the magnetic thresholds a mix of output pulse widths representing the referring magnetic values occur. for similar reasons pulse widths of 90, 180, 360, 720s can be observed occasionally for single pulses at b limit .
tle4942, tle4942c tle4942 - tle4942c data sheet february 2002 3 5. behaviour close to speed v5 (f el-bit = ca. 117 hz) signal imperfections like duty cycle and jitter result in a mix of output pulses with and without assembly bit (el) information. input signal duty cycles apart from 50% increase the range where both pulse widths appear. 6. dependency of direction detection on input signal pitch: the direction detection is optimised for a target wheel pitch of 5mm where it will work down to b warning . (b warning and direction detection thresholds meet at 5mm pitch.) for pitches other than 5mm the magnetic input signal has to be increased to compensate for the inevitable signal attenuation. degradation of speed and direction signal at sinusoidal input signals = f(pitch) 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 23456789101112 pitch / mm degradation factor speed direction
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