TLE 4923

Semiconductor Group

4

1998-04-29

Functional Description

The Differential Hall sensor IC detects the motion and position of ferromagnetic and

permanent magnet structures by measuring the differential flux density of the magnetic

field. To detect ferromagnetic objects the magnetic field must be provided by a back

biasing permanent magnet (south or north pole of the magnet attached to the rear

unmarked side of the IC package).

Using an external capacitor the generated Hall voltage signal is slowly adjusted via an

active high pass filter with low frequency cut-off. This causes the output to switch into a

biased mode after a time constant is elapsed. The time constant is determined by the

external capacitor. Filtering avoids aging and temperature influence from Schmitt-trigger

input and eliminates device and magnetic offset.

The TLE 4923 can be exploited to detect toothed wheel rotation in a rough environment.

Jolts against the toothed wheel and ripple have no influence on the output signal.

The on and off state of the IC are indicated by high and low current consumption.

Circuit Description (see Figure 2)

The TLE 4923 is comprised of a supply voltage reference, a pair of Hall probes spaced

at 2.5 mm, differential amplifier, filter for offset compensation, Schmitt-trigger, and a

switched current source.

The TLE 4923 was designed to have a wide range of application parameter

variations. Differential fields up to

± 40 mT can be detected without influence to

the switching performance. The pre-induction field can either come from a

magnetic south or north pole, whereby the field strength up to 500 mT or more will

not influence the switching points

enables a superior sensitivity and accuracy over the temperature range. Finally,

the

optimized

piezo

compensation

and

the

integrated

dynamic

offset

compensation enable easy manufacturing and elimination of magnet offsets.

Protection is provided at the input/supply (pin 1) for reverse polarity.

1)

Differential bias fields exceeding

± 20 mT, e. g. caused by a misaligned magnet, should be avoided.