TLE4923 Datasheet, PDF (4/18 Pages) Siemens Semiconductor Group – Dynamic Differential Hall Effect Sensor IC

TLE 4923
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 points¹⁾. The improved temperature compensation
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.}
Semiconductor Group
4
1998-04-29