ATS667LSG
True Zero-Speed, High Accuracy Gear Tooth Sensor IC
Continuous Update of Switchpoints
Switchpoints are the threshold levels of the differential internal As shown in panel C of figure 4, threshold levels for the ATS667
analog signal, VPROC, at which the device changes output signal switchpoints are established as a function of the peak input signal
state.ThevalueofVPROC isdirectlyproportionaltothemagneticflux levels. The ATS667 incorporates an algorithm that continuously
density, B, induced by the target and sensed by the Hall elements. monitors the input signal and updates the switching thresholds
As VPROC rises through a certain limit, referred to as the operate accordingly with limited inward movement of VPROC
.
The
point, BOP, the output state changes from high to low. As VPROC switchpoint for each edge is determined by the detection of the
falls below BOP to a certain limit, the release point, BRP, the output previous two signal edges. In this manner, variations are tracked
state changes from low to high.
in real time.
(A) TEAG varying; cases such as
(B) Internal analog signal, VPROC
,
eccentric mount, out-of-round region,
normal operation position shift
typically resulting in the IC
V+
Smaller
TEAG
Smaller
TEAG
Larger
TEAG
Target
Target
Hysteresis Band
(Delimited by switchpoints)
Smaller
TEAG
Larger
TEAG
IC
IC
0
360
Target Rotation (°)
(C) Referencing the internal analog signal, VPROC, to continuously update device response
BOP(#1) BOP(#2) BOP(#3)
BOP(#4)
Pk(#9)
Pk(#1)
V+
Determinant
BHYS
Switchpoint
Pk(#3)
Pk(#7)
Peak Values
BOP(#1)
BRP(#1)
Pk(#1), Pk(#2)
Pk(#2), Pk(#3)
Pk(#5)
1
2
3
VPROC(BOP)
(#1)
VPROC(BOP)
(#2)
BHYS(#3)
VPROC(BOP)
(#4)
VPROC(BOP)
(#3)
BOP(#2)
BRP(#2)
Pk(#3), Pk(#4)
Pk(#4), Pk(#5)
BHYS(#1)
VPROC(BRP)
BHYS(#4)
VPROC(BRP)
BHYS(#2)
VPROC(BRP)
(#3)
(#4)
VPROC(BRP)
(#1)
(#2)
BOP(#3)
BRP(#3)
Pk(#5), Pk(#6)
Pk(#6), Pk(#7)
Pk(#6)
Pk(#4)
BOP(#4)
BRP(#4)
Pk(#7), Pk(#8)
Pk(#8), Pk(#9)
Pk(#8)
BRP(#3)
Pk(#2)
4
BRP(#1)
BRP(#2)
BRP(#4)
Figure 4. The Continuous Update algorithm allows the Allegro IC to 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, 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
inward signal variation the IC is able to react to over a single transition. The algorithm is used to 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 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
switchpoints based on the fluctuation of VPROC, as shown in panel C.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
9
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
