ATS657LSHTN-T datasheet(9/15 Pages) ALLEGRO

9 / 15 page

Dynamic, Self-Calibrating, Threshold-Detecting, Differential

Speed and Direction Hall-Effect Gear Tooth Sensor IC

ATS657

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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.

Continuous Update of Switchpoints

(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)

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.

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)

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