ATS667LSG datasheet(9/14 Pages) ALLEGRO

9 / 14 page

True Zero-Speed, High Accuracy Gear Tooth Sensor IC

ATS667LSG

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Continuous Update of Switchpoints

Switchpoints are the threshold levels of the differential internal

analog signal, VPROC, at which the device changes output signal

state.The value ofVPROCisdirectlyproportionaltothemagneticflux

density, B, induced by the target and sensed by the Hall elements.

As VPROC rises through a certain limit, referred to as the operate

point, BOP, the output state changes from high to low. As VPROC

falls below BOP to a certain limit, the release point, BRP, the output

state changes from low to high.

As shown in panel C of figure 4, threshold levels for the ATS667

switchpoints are established as a function of the peak input signal

levels. The ATS667 incorporates an algorithm that continuously

monitors the input signal and updates the switching thresholds

accordingly with limited inward movement of VPROC. The

switchpoint for each edge is determined by the detection of the

previous two signal 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 IC

360

Target Rotation (°)

Hysteresis Band

(Delimited by switchpoints)

V+

Larger

TEAG

Smaller

TEAG

Target

Larger

TEAG

Target

Smaller

TEAG

Smaller

TEAG

Pk(#4)

Pk(#5)

Pk(#7)

Pk(#9)

Pk(#2)

Pk(#3)

Pk(#1)

Pk(#6)

Pk(#8)

HYS(#4)

HYS(#3)

V+

BRP(#1)

BOP(#1)

BRP(#2)

BRP(#3)

BOP(#3)

BRP(#4)

BOP(#4)

BOP(#2)

PROC(BOP)

(#1)

PROC(BOP)

(#2)

PROC(BOP)

(#3)

PROC(BOP)

(#4)

PROC(BRP)

(#1)

PROC(BRP)

(#2)

PROC(BRP)

(#3)

PROC(BRP)

(#4)

HYS(#1)

HYS(#2)

BHYS

Switchpoint

Determinant

Peak Values

BOP(#1)

Pk(#1), Pk(#2)

BRP(#1)

Pk(#2), Pk(#3)

BOP(#2)

Pk(#3), Pk(#4)

BRP(#2)

Pk(#4), Pk(#5)

BOP(#3)

Pk(#5), Pk(#6)

BRP(#3)

Pk(#6), Pk(#7)

BOP(#4)

Pk(#7), Pk(#8)

BRP(#4)

Pk(#8), Pk(#9)

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.

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