ATS657 Просмотр технического описания (PDF) - Allegro MicroSystems
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ATS657 Datasheet PDF : 15 Pages
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ATS657
Dynamic, Self-Calibrating, Threshold-Detecting, Differential
Speed and Direction Hall-Effect Gear Tooth Sensor IC
Continuous Update of Switchpoints
The processed differential internal analog signal, VPROC , of each
of the two channels is used to determine switchpoints, at which
the device determines direction information and changes to out-
put signal polarity. Because the value of VPROC is directly propor-
tional to the differential magnetic flux density, BDIFF, induced by
the target and sensed by the Hall elements, the switchpoints occur
at threshold levels that correspond to certain levels of BDIFF.
The operate point, BOP , occurs when VPROC rises through a cer-
tain limit, VPROC(BOP) . When BOP occurs, the channel internally
switches from low to high. When VPROC falls below VPROC(BOP)
through a certain limit, VPROC(BRP) , the release point, BRP,
occurs and the channel state switches from high to low.
As shown in panel C of figure 4, the threshold levels for the
ATS657 switchpoints are established as a function of the two
previous signal peaks detected. The ATS657 incorporates an
algorithm that continuously monitors VPROC and then updates the
switching thresholds to correspond to any amplitude reduction.
For any given target edge transition, the change in threshold level
is limited. Each channel operates in this manner, independent of
each other, so independent switchpoint thresholds are calculated
for each channel.
V+
Smaller
TEAG
Larger
TEAG
Smaller
TEAG
Target
Target
Smaller
IC
TEAG
Larger
IC
TEAG
(A) TEAG varying; cases such as eccentric mount,
out-of-round region, normal operation position shift
Hysteresis Band
(Delimited by switchpoints)
0
360
Target Rotation (°)
(B) Internal analog signal, VPROC, typically resulting in the IC
BHYS Switchpoint
Determinant
Peak Values
V+
1
BOP(#1)
BRP(#1)
Pk(#1), Pk(#2)
Pk(#2), Pk(#3)
2
BOP(#2)
BRP(#2)
Pk(#3), Pk(#4)
Pk(#4), Pk(#5)
3
BOP(#3)
BRP(#3)
Pk(#5), Pk(#6)
Pk(#6), Pk(#7)
BOP(#4)
Pk(#7), Pk(#8)
4
BRP(#4)
Pk(#8), Pk(#9)
Pk(#1)
BOP(#1)
Pk(#3)
BOP(#2)
BOP(#3)
Pk(#7)
BOP(#4)
Pk(#9)
Pk(#5)
VPROC(BOP)(#1)
VPROC(BOP)(#2)
BHYS(#3)
VPROC(BOP)(#4)
BHYS(#1)
VPROC(BOP)(#3)
BHYS(#2)
BHYS(#4)
VPROC(BRP)(#1)
VPROC(BRP)(#2)
VPROC(BRP)(#3)
VPROC(BRP)(#4)
Pk(#2)
Pk(#4)
BRP(#1)
Pk(#6)
BRP(#2)
Pk(#8)
BRP(#3)
BRP(#4)
(C) Referencing the internal analog signal, VPROC, to continuously update device response
Figure 4. The Continuous Update algorithm allows the Allegro IC to immediately interpret and adapt to 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). Not detailed in the figure are the boundaries for peak capture DAC movement which
intentionally limit the amount of internal signal variation the IC is able to react to over a single transition. The algorithm is used to dynamically establish
and subsequently update the device switchpoint levels (VPROC(BOP) and VPROC(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 IC 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 switchpoint
levels based on the fluctuation of VPROC, as shown in panel C.
Allegro MicroSystems, Inc.
9
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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