TLE4953x

Functional Description

Data Sheet

10

Version 4.1, 2018-01-02

After successful correction of the offset, the output switching is in calibrated mode. Switching occurs at adaptive

threshold-crossover. It is only affected by the propagation delay time of the signal path, which is mainly determined

by the noise limiting filter. Signals which are below a predefined threshold

ΔBLimit are not detected. This prevents

unwanted switching.

The adaptive hysteresis is linked to the PGA state. Therefore the system is able to suppress switching if vibration

or noise signals are smaller than the adaptive hysteresis.

The switching and direction information is fed into the DSP and the output encoder. The pulse length of the High

output current is generated according to the rotational speed and the direction of rotation

2.4

Direction signal circuitry

The differential signal between a third Hall probe and the mean value of the differential Hall probe pair is obtained

from the direction input amplifier. This signal is digitized by the direction ADC and fed into the digital circuitry.

There, the phase of the signal referring to the speed signal is analyzed and the direction information is forwarded

to the output encoder. The phase is identified by calculating the size of the direction signal at two consecutive zero

crossings of the speed signal. This is done by subtracting the current direction signal from the internal stored value

which has been taken from the previous magnetic edge.

Depending on the phase shift between the direction signal and the speed signal a positive or a negative value

occur. The information if the new direction calculation takes place at a rising or a falling magnetic edge allows

together with the algebraic sign of the calculated direction signal a reliable direction detection.

The first pulse after power is always a speed pulse as there is no stored direction information available.

2.5

Vibration suppression algorithm

The magnetic signal amplitude and the direction information is used for detection of parasitic magnetic signals.

Unwanted magnetic signals can be caused by angular or airgap vibrations for instance. If an input signal is clearly

detected as a vibration signal, the output of pulses will be suppressed.

A magnetic input signal is classified as parasitic vibration signal if

a. the speed signal amplitude is smaller than the internal hysteresis or

b. the direction signal amplitude is smaller than the internal limit or

c. the direction signal consists of alternating left/right information

The quality of vibration suppression (according a & b) depends on the hysteresis limits and on the magnitude of

the magnetic signal. The bigger the hysteresis the better the suppression of parasitc signals.

For parasitic signals where items above (a. to c.) are not clearly applicable or at other more rare cases (e.g. IC

startup) vibration suppression is not guaranteed. The performance of the direction detection and vibration

suppression algorithm depends on the used magnetic circuit and as well on the used target wheel and need to be

evaluated.

Please ask for application support if you have questions on the vibration suppresion algorithm.