Data Sheet

17

1.10

2018-09-13

TLE4929C Crankshaft Sensor

Fully Programmable Crankshaft Sensor

3.4

Hysteresis Concept

Figure 9

Hidden Hysteresis in protocol-variant without direction detection

The prefered switching behavior for crankshaft application in terms of hysteresis is called hidden adaptive

hysteresis. For reason of long notches or long teeth there is the EEPROM possibility to go for visible hysteresis

as well. Another EEPROM possibility is fixed hysteresis, which allows robustness against metalic flakes

attached by the back-bias-magnet.

Hidden adaptive hysteresis means, the output always switches at the same level, centered between upper and

lower hysteresis. These hysteresis thresholds needs to be exceeded and are used to enable the output for the

next following switching event. For example, if the differential magnetic field crosses the lower hysteresis

level, then the output is able to switch at the zero crossing. Next following upper hysteresis needs to be

exceeded again in order to enable for the next switching. Furthermore, the function of half hysteresis

maintains switching whenever the upper hysteresis level is not exceeded, but the lower hysteresis level is

crossed again, then the output is allowed to switch, so that no edge is lost. However, this causes additional

phase error, see Figure 9.

Doing an adaptive hysteresis gives advantage at small airgap (large signal) to have big hysteresis. Compared

with fixed hysteresis a small vibration cannot cause additional switching. According Figure 10 the adaptive

hysteresis is calculated as 25% of the differential Speed-signal peak to peak. The minimum hysteresis is

derived from EEPROM-setting ”HYST_MIN”.

t

switch point

switch point (half hystersis)

BHYS/2

BHYS/2

t