ATS128 datasheet(19/25 Pages) ALLEGRO

19 / 25 page

Highly Programmable, Back-Biased,

Hall-Effect Switch with TPOS Functionality

ATS128LSE

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

BOP Selection

The ATS128 allows accurate trimming of the magnetic operate

point, BOP , within the application. This programmable feature

reduces effects due to mechanical placement tolerances and

improves performance when used in proximity or gear tooth sens-

ing applications.

BOP can be set to any value within the range allowed by the

BOPSEL registers. This includes switchpoints of south or north

polarity, and switchpoints at or near the zero crossing point for

B. However, switching is recommended only within the air gap

limits specified in the Operating Characteristics table.

Trimming of BOP is typically done in two stages. In the first

stage, BOP is adjusted temporarily using the Try mode program-

ming features, to find the fuse value that corresponds to the

optimum BOP. After a value is determined, then it can be perma-

nently set using the Blow mode features.

As an aid to programming the ATS128 has several options avail-

able in Try Mode for adjusting the BOP parameter. As shown in

figure 14, these allow trimming of BOP for operation in north or

south polarity magnetic fields. In addition the BOP parameter can

either trim-up, start at the BOP minimum value and increase to

the maximum value, or trim-down, starting at the BOP maximum

value and decreasing to the minimum value.

The Trim Up-Counting and Trim Down-Counting features can

simplify switchpoint calibration by allowing the user to find

the codes for both the magnetic operation point, BOP, and the

magnetic release point, BRP. As an example, consider using the

ATS128 as a proximity sensor to detect rotational displacement

of a ferromagnetic target (see figure 15). When the ferromagnetic

target is centered opposite the device branded face, its location

is considered homed (0 mm displacement). If the target rotates

a certain distance, ± θ, in either direction, the sensor IC output

should change state.

(A) BOP Positive, Trim Up-Counting Register

(B) BOP Positive, Trim Down-Counting Register

(D) BOP Negative, Trim Down-Counting Register

BOP(max)

B+ (south)

B– (north)

BOP(max)

B+ (south)

B– (north)

B+ (south)

B– (north)

B+ (south)

B– (north)

BOP(min)

BOP(max)

BOP(min)

Try Mode, Bit Field Code

255

Try Mode, Bit Field Code

255

Try Mode, Bit Field Code

255

Try Mode, Bit Field Code

255

BOP Setpoint

Figure 14. BOP profiles for each of the four BOP Selection virtual registers available in Try mode.

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