Self-Calibrating TPOS Gear Tooth Sensor ICs
Optimized for Automotive Cam Sensing Applications
ATS673 and
ATS674
13
Allegro MicroSystems, LLC
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Pk
4
Pk
5
Pk
7
Pk
9
Pk
2
Pk
3
Pk
1
Pk
6
Pk
8
B
RP1
B
OP1
B
RP2
B
RP3
B
OP3
B
RP4
B
OP4
B
HYS
B
HYS
B
HYS
B
HYS
t+
V+
B
HYS
B
HYS
B
HYS
B
OP2
B
HYS
(A) TEAG varying; cases such as
eccentric mount, out-of-round region,
normal operation position shift
(B) Internal analog signal, V
PROC
,
typically resulting in the IC
0
360
Target Rotation (?
Hysteresis Band
(Delimited by switchpoints)
V+
Larger
TEAG
Smaller
TEAG
IC
Target
Larger
TEAG
Target
IC
Smaller
TEAG
Smaller
TEAG
Figure 9. The Continuous Update algorithm allows the Allegro IC to immediately interpret and adapt to significant variances in the magnetic field gener-
ated 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 (B
OP
and B
RP
). The hysteresis, B
HYS(#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, V
PROC
.
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, V
PROC
, shown in panel B. The Continuous Update algorithm is used to establish accurate switchpoints
based on the fluctuation of V
PROC
, as shown in panel C.
(C) Referencing the internal analog signal, V
PROC
, to continuously update device response
Switchpoint
Determinant
Peak Values
B
OP1
Pk
1
, Pk
2
B
RP1
Pk
2
, Pk
3
B
OP2
Pk
3
, Pk
4
B
RP2
Pk
4
, Pk
5
B
OP3
Pk
5
, Pk
6
B
RP3
Pk
6
, Pk
7
B
OP4
Pk
7
, Pk
8
B
RP4
Pk
8
, Pk
9
Update
The ATS673 and ATS674 incorporate an algorithm that continu-
ously monitors the system and updates the switching thresholds
accordingly. The switchpoint for each transition is determined
by the previous two transitions. Because variations are tracked in
real time, the IC has high immunity to target run-out and retains
excellent accuracy and functionality in the presence of both
run-out and transient mechanical events. Figure 9 shows how the
devices use historical data to provide the switching thresholds
for a given edge.