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AATS643LSH_06 Datasheet, PDF (10/16 Pages) Allegro MicroSystems – Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update
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ATS643LSH
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
VPROC is directly proportional to the magnetic flux density, B,
induced by the target and sensed by the Hall elements. When
VPROC transitions through a switchpoint from the appropriate
higher or lower level, it triggers sensor switch turn-on and turn-
off. As shown in figure 3, when the switch is in the off state, as
VPROC rises through a certain limit, referred to as the operate
point, BOP, the switch toggles from off to on. When the switch is
in the on state, as VPROC falls below BOP to a certain limit, the
release point, BRP, the switch toggles from on to off.
As shown in panel C of figure 4, threshold levels for the ATS643
switchpoints are established dynamically as function of the
peak input signal levels. The ATS643 incorporates an algorithm
that continuously monitors the system and updates the switch-
ing thresholds accordingly. The switchpoint for each edge is
determined by the detection of the previous two edges. In this
manner, variations are tracked in real time.
(A) TEAG varying; cases such as
eccentric mount, out-of-round region,
normal operation position shift
(B) Internal analog signal, VPROC,
typically resulting in the sensor
V+
Smaller
TEAG
Larger
TEAG
Smaller
TEAG
Target
Target
Sensor
Smaller
TEAG
Sensor
Larger
TEAG
0
Hysteresis Band
(Delimited by switchpoints)
360
Target Rotation (°)
(C) Referencing the internal analog signal, VPROC, to continuously update device response
BHYS
1
2
3
4
Switchpoint
BOP(#1)
BRP(#1)
BOP(#2)
BRP(#2)
BOP(#3)
BRP(#3)
BOP(#4)
BRP(#4)
Determinant
Peak Values
Pk(#1), Pk(#2)
Pk(#2), Pk(#3)
Pk(#3), Pk(#4)
Pk(#4), Pk(#5)
Pk(#5), Pk(#6)
Pk(#6), Pk(#7)
Pk(#7), Pk(#8)
Pk(#8), Pk(#9)
V+
Pk(#1)
Pk(#3)
Pk(#7)
Pk(#9)
BOP(#1)
Pk(#5)
BOP(#2)
BOP(#3)
BRP(#1)
BRP(#2)
BOP(#4)
BRP(#3)
BRP(#4)
Pk(#2)
Pk(#4)
BHYS(#1)
Pk(#6)
BHYS(#2)
Pk(#8)
BHYS(#3)
BHYS(#4)
t+
Figure 4. The Continuous Update algorithm allows the Allegro sensor to immediately interpret and adapt to significant variances in the magnetic field
generated by the target as a result of eccentric mounting of the target, out-of-round target shape, elevation due to lubricant build-up in journal gears, and
similar dynamic application problems that affect the TEAG (Total Effective Air Gap). The algorithm is used to dynamically establish and subsequently
update the device switchpoints (BOP and BRP). The hysteresis, BHYS(#x), at each target feature configuration results from this recalibration, ensuring that
it remains properly proportioned and centered within the peak-to-peak range of the internal analog signal, VPROC.
As shown in panel A, the variance in the target position results in a change in the TEAG. This affects the sensor as a varying magnetic field, which
results in proportional changes in the internal analog signal, VPROC, shown in panel B. The Continuous Update algorithm is used to establish accurate
switchpoints based on the fluctuation of VPROC, as shown in panel C.
Allegro MicroSystems, Inc.
10
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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