TLE4941, TLE4941C

TLE4941 - TLE 4941C Data Sheet

Febrary 2002

2

Functional Description

The differential hall sensor IC detects the motion of ferromagnetic and permanent

magnet structures by measuring the differential flux density of the magnetic field. To

detect the motion of ferromagnetic objects the magnetic field must be provided by a

back biasing permanent magnet. Either south or north pole of the magnet can be

attached to the rear unmarked side of the IC package.

Magnetic offsets of up to +/- 20mT and device offsets are cancelled by a self-

calibration algorithm. Only a few transitions are necessary for self-calibration. After

the initial calibration sequence switching occurs when the input signal is crossing the

arithmetic mean of its max and min value. (E.g. zero-crossing for sinusoidal signals)

The ON and OFF state of the IC are indicated by High and Low current

consumption.

Circuit Description

The circuit is supplied internally by a 3V voltage regulator. An on-chip oscillator

serves as clock generator for the digital part of the circuit.

TLE4941 signal path is comprised of a pair of hall probes, spaced at 2.5mm, a

differential amplifier including a noise-limiting low-pass filter and a comparator

feeding a switched current output stage. In addition an offset cancellation feedback

loop is provided by a signal-tracking A/D converter, a digital signal processor (DSP)

and an offset cancellation D/A converter.

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

DSP. 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.

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

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

occurs at zero-crossing. It is only affected by the (small) remaining offset of the

comparator and by the remaining propagation delay time of the signal path, mainly

determined by the noise-limiting filter. Signals below a defined threshold

∆B

not detected to avoid unwanted parasitic switching.