TLE4953

TLE4953C

Data Sheet

5

V 4.0, 2010-04

states), leading to a change in phase shift between magnetic input signal and output

signal. After that consecutive output edges should have a nominal delay of about 360°.

During the uncalibrated mode the offset value is calculated by the peak detection

algorithm as described below.

The differential input signal is digitized in the speed A/D converter and fed into the DSP

part of the circuit. The minimum and maximum values of the input signal are extracted

and their corresponding arithmetic mean value is calculated. The offset of this mean

value is determined and fed into the offset cancellation DAC.

The offset update takes place when two valid extremes are found and the direction of the

update has the same orientation as the magnetic slope (valid for calibrated mode). For

example an positive offset update is only possible on a rising magnetic edge. The offset

update is done independant from the output switching.

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

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.

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.