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TLE4921-5U
Hall Sensors
Dynamic Differential Hall Effect Sensor ICTLE4921-5U
Bipolar IC
FeaturesAdvanced performanceHigh sensitivitySymmetrical thresholdsHigh piezo resistivityReduced power consumptionSouth and north pole pre-induction possible• AC coupled
• Digital output signalTwo-wire and three-wire configuration possible
• Large temperature range
• Large airgapLow cut-off frequency
• Protection against overvoltageProtection against reversed polarityOutput protection against electrical disturbances
The differential Hall Effect sensor TLE 4921-5U provides a high sensitivity and a
superior stability over temperature and symmetrical thresholds in order to achieve a
stable duty cycle. TLE 4921-5U is particularly suitable for rotational speed detection
and timing applications of ferromagnetic toothed wheels such as anti-lock braking
systems, transmissions, crankshafts, etc. The integrated circuit (based on Hall
effect) provides a digital signal output with frequency proportional to the speed of
rotation. Unlike other rotational sensors differential Hall ICs are not influenced by
radial vibration within the effective airgap of the sensor and require no external
signal processing.
TLE4921-5U
Pin Configuration(view on branded side of component)
Figure 1
Pin Definitions and Functions
TLE4921-5U
Figure 2 Block Diagram
TLE4921-5U
Functional DescriptionThe 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 a low cut-off frequency. 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 ageing and temperature
influence from Schmitt-trigger input and eliminates device and magnetic offset.
The TLE 4921-5U 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.
Furthermore, the TLE 4921-5U can be operated in a two-wire as well as in a three-
wire-configuration.
The output is logic compatible by high/low levels regarding on and off.
Circuit Description (see Figure 2)The TLE 4921-5U 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 an open collector output.
The TLE 4921-5U was designed to have a wide range of application parameter
variations. Differential fields up to ±±±± 80 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. The improved temperature
compensation enables a superior sensitivity and accuracy over the
temperature range. Finally the optimised 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 overvoltage and reverse
polarity and against over-stress such as load dump, etc., in accordance with
ISO-TR 7637 and DIN 40839. The output (pin 2) is protected against voltage peaks
and electrical disturbances.
TLE4921-5U
Absolute Maximum Ratingsj = – 40 to 150 °C
Electro Magnetic Compatibilityref. DIN 40839 part 1; test circuit 1
1) Reverse current < 10mA
Note: Stresses above those listed here may cause permanent damage to the
device. Exposure to absolute maximum rating conditions for extended periods
may affect device reliability.
TLE4921-5U
ESD ProtectionHuman Body Model (HBM) tests according to:
Operating RangeNote: In the operating range the functions given in the circuit description are
fulfilled.
AC/DC Characteristics
TLE4921-5U
AC/DC Characteristics (cont’d)2) The Current consumption characteristic will be different and the specified values can slightly change
3) Leakage currents at pin 4 should be avoided. The bias shift of Bm caused by a leakage current IL can be
calculated by: ∆Bm = (IL × RC(T))/SC(T)
4) For higher ∆B the values may exceed the limits like following |∆Bm| < |0.05 × ∆B|
5) Depends on filter capacitor CF. The cut-off frequency is given by f = 1/(2π × RC × CF).
The switching points are guaranteed over the whole frequency range, but amplitude modification and
phase shift due to the 1st order high-pass filter have to be taken into account.
Note: The listed characteristics are ensured over the operating range of theintegrated circuit. Typical characteristics specify mean values expected over
the production spread. If not otherwise specified, typical characteristics apply
TLE4921-5U
Figure 3 Test Circuit 1
Figure 4 Test Circuit 2
TLE4921-5U
Application ConfigurationsTwo possible applications are shown in
Figure 7 and Figure 8 (Toothed and
Magnet Wheel).
The difference between two-wire and three-wire application is shown in Figure 9.
Gear Tooth SensingIn the case of ferromagnetic toothed wheel application the IC has to be biased by
the south or north pole of a permanent magnet (e.g. SmCO5 (Vacuumschmelze
VX145)) with the dimensions 8 mm × 5 mm × 3 mm) which should cover both Hall
probes.
The maximum air gap depends onthe magnetic field strength (magnet used; pre-induction) andthe toothed wheel that is used (dimensions, material, etc.; resulting differential
field)
Figure 5 Sensor Spacing
TLE4921-5U
Figure 7 TLE 4921-5U, with Ferromagnetic Toothed Wheel
TLE4921-5U
Figure 9 Application Circuits
TLE4921-5U
Figure 10 System Operation
