TLE4942, TLE4942C

TLE4942 - TLE4942C Data Sheet

February 2002

6

Circuit Description

The circuit is supplied internally by a voltage regulator. An on-chip oscillator serves

as a clock generator for the DSP and the output encoder.

Speed signal circuitry:

TLE4942 speed signal path comprises of a pair of Hall Effect probes, separated from

each other by 2.5mm, a differential amplifier including noise limiting low-pass filter,

and a comparator triggering a switched current output stage. An offset cancellation

feedback loop is provided through a signal-tracking A/D converter, a digital signal

processor (DSP), and an offset cancellation D/A converter.

During the power-up phase (uncalibrated mode) the output is disabled.

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.

After successful correction of the offset, the output switching is enabled.

In running mode (calibrated mode) the offset correction algorithm of the DSP is

switched into a low-jitter mode, thereby avoiding oscillation of the offset DAC LSB.

Switching occurs at zero-crossover. It is only affected by the small residual offset of

the comparator and 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

∆B

The comparator also detects whether the signal amplitude exceeds

∆B

∆B

This 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, the direction of

rotation and the magnetic field strength.

Direction signal circuitry:

The differential signal between a third Hall probe and the mean 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 DSP circuitry. There, the phase of the signal referring

to the speed signal is analyzed and the direction information is forwarded to the

output encoder.