TLE4943C datasheet(23/48 Pages) INFINEON

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TLE4943C

Data Sheet

V 1.2, July 2018

2.8

Operating Modes and States

The basic operation of the TLE4943C is to measure the differential magnetic field of a rotating target wheel and

generate an output signal which represents the wheel speed and provides information about rotation direction and

signal quality. The IC has a three level current interface. The functionality of the TLE4943C can be distinguished

in two different phases: uncalibrated and calibrated mode.

2.8.1

Uncalibrated and Calibrated Mode

After an initial calibration delay time td_input, the differential magnetic signal dB is tracked by an analog to digital

converter (ADC) and monitored within the digital circuit. For detection the signal needs to exceed the internal

threshold DNC (digital noise constant). When the signal slope is identified as a falling (or rising) edge and the

signal change exceeds the DNC, the first extrema is located and first output pulse is triggered. The digital noise

constant value is changed accordingly to magnetic field amplitude, leading to a change in phase shift between

magnetic input signal and output signal. This value of the digital noise constant is determined by the signal

amplitude. First DNC (=2 x dBlimit), indicated as arrows in figure below. A second output is triggered when the

signal change exceeds again the value of the new DNC (calulated by (min1 + max 1)/2)in the following rising

(respectively falling) edge. When a maximum and minimum was found an offset correction will take place. This

leads to a phase shift of output signal and the sensor enters the calibrated mode. In calibrated mode switching is

triggered by the zero crossing of the differential magnetic signal. The min/max detection is reduced to 1/4 of peak-

peak. In calibrated mode minimal DNC is 2 x dBlimit .Out of this consecutive speed pulses have a nominal delay of

about 180°.

Handling of additional information bits in uncalibrated and calibrated mode:

Signal amplitude measurement: SLM is valid if two valid extrema are found (the first extrema after power on is

invalid). Latest with fourth protocol SLM is valid.

Startup at high frequencies could lead to shortened protocol. The bit suppression according Chapter “Bit Stump

Suppression” is executed.

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