3046 Datasheet, PDF (7/8 Pages) Allegro MicroSystems – HALL EFFECT GEAR-TOOTH SENSORS ZERO SPEED

3046, 3056, AND 3058
HALL EFFECT
GEAR-TOOTH SENSORS
–ZERO SPEED
Figure 5
DIFFERENTIAL FLUX DENSITY
2000
1500
1000
500
0
-500
-1000
-1500
-2000
0
200
0.025
0.050
0.075
0.100
AIRGAP FROM PACKAGE FACE IN INCHES
0.125
Dwg. GH-035
150
100
50
0
-50
-100
-150
-200
0.070
0.080
0.090
0.100
0.110
AIRGAP FROM PACKAGE FACE IN INCHES
0.120
Dwg. GH-036
SENSOR LOCATIONS
(±0.005” [0.13 mm] die placement)
ACTIVE AREA DEPTH
0.015"
0.38 mm
NOM
0.088"
2.23 mm
Pole Piece Design. A pole piece may be used at the face of the
magnet to smooth out the magnet-face offsets. A 0.020” (0.51 mm)
thick, soft-iron pole piece will bring the field non-uniformity down to
the ±1%-to-±3% range. Note that pole pieces will minimize but not
eliminate the non-uniformity in the magnet face field. Front pole pieces
will almost always result in a reduced maximum air gap.
Ferrous Targets. The best ferrous targets are made of cold-rolled
low-carbon steel. Sintered-metal targets are also usable, but care
must be taken to ensure uniform material composition and density.
The teeth or slots of the target should be cut with a slight angle
so as to minimize the abruptness of transition from metal to air as the
target passes by the sensor. Sharp transitions will result in magnetic
overshoots that can result in false triggering.
Gear teeth larger than 0.10” (2.54 mm) wide and at least 0.10”
(2.54 mm) deep provide reasonable working air gaps and adequate
change in magnetic field for reliable switching. Generally, larger teeth
and slots allow a larger air gap. A gear tooth width approximating the
spacing between sensors (0.088” or 2.24 mm) requires special care in
the system design and assembly techniques.
ASSEMBLY TECHNIQUES
Due to magnet face non-uniformities and device variations, it is
recommended that applications requiring precision switching utilize a
mechanical optimization procedure during assembly. Without a pole
piece, the inherent magnet face offsets can be used to pre-bias the
magnetic circuit to obtain any desired operating mode. This is
achieved by physically changing the relative position of the magnet
behind the sensor to achieve the desired system performance objec-
tive. For example, with a rotating ABS gear, the objective might be a
50% duty cycle at maximum air gap. Similar objectives can be set for
ignition (crank and cam position) sensing systems.
Non-precision speed sensing applications do not require optimiza-
tion. For applications where mechanical optimization is not feasible,
non-zero speed devices such as the UGN/UGS3059KA ac-coupled
gear-tooth sensor are available.
0.075"
E1
1.89 mm
E2
A
BRANDED
SURFACE 1
2
3
Dwg. MH-002-8D
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