ATS622LSB datasheet(9/17 Pages) ALLEGRO

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115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

ATS660LSB

TRUE ZERO-SPEED,

HALL-EFFECT ADAPTIVE

GEAR-TOOTH SENSOR

DEVICE DESCRIPTION — Continued

In addition to the gain control circuitry, the device also

has provisions to zero out chip, magnet, and installation

offsets. This is accomplished using two D-to-A converters

that capture the peak and valley of the signal and use them

as a reference for the switching comparator. This allows

the switch points to be precisely controlled independent of

air gap or temperature.

The two Hall transducers and the electronics are inte-

grated on a single silicon substrate using a proprietary

BiCMOS process.

Solution advantages. The ATS660LSB true zero-

speed detecting gear-tooth sensor uses a differential Hall-

element configuration. This configuration is superior in

most applications to a classical single-element GTS. The

single-element configuration commonly used requires the

detection of an extremely small signal (often <100 G) that

is superimposed on an extremely large back biased field,

often 1500 G to 3500 G. For most gear configurations, the

back-biased field values change due to concentration

effects, resulting in a varying baseline with air gap, with

eccentricities, and with vibration. The differential con-

figuration eliminates the effects of the back-biased field

through subtraction and, hence, avoids the issues presented

by the single Hall element. The signal-processing circuitry

also greatly enhances the functionality of this device.

Other advantages are

s temperature drift* — changes in temperature do not

greatly affect this device due to the stable amplifier design

and the offset rejection circuitry,

s timing accuracy/duty cycle variation due to air gap*

— the accuracy variation caused by air-gap changes is

minimized by the self-calibration circuitry. A two-to-three

times improvement can be seen over conventional zero-

crossing detectors,

s dual edge detection — because this device references

the positive and negative peaks of the signal, dual edge

detection is guaranteed,

s immunity to magnetic overshoot — the air-gap

independent hysteresis minimizes the impact of overshoot

on the switching of device output,

s response to surface defects in the gear — the gain-

adjust circuitry reduces the effect of minor gear anomalies

that would normally causes false switching,

s immunity to vibration and backlash — the gain-adjust

circuitry keeps the hysteresis of the device roughly propor-

tional to the peak-to-peak signal. This allows the device to

have good immunity to vibration even when operating at

close air gaps,

s immunity to gear run out — the differential-sensor

configuration eliminates the base-line variations caused by

gear run out, and

s use with stamped-gear configurations — the high-

sensitivity switch points allow the use of stamped gears.

The shallow mechanical slopes created by the stamping

process create an acceptable magnetic gradient down to

zero speed. The surface defects caused by stamping the

gear are ignored through the use of gain control circuitry.

Operation versus air-gap/tooth geometry. Operat-

ing specifications are impacted by tooth size, valley size

and depth, gear material, and gear thickness. In general,

the following guidelines should be followed to achieve

greater than 2 mm air gap from the face of unit:

s tooth width (T) > 2 mm;

s valley width (p

C - T) > 2 mm;

s valley depth (h

t) > 2 mm;

s gear thickness (F) > 3 mm; and the

s gear material must be low-carbon steel.

Signal duty cycle. For regular tooth geometry, precise

duty cycle is maintained over the operating air-gap and

temperature range due to an extremely good symmetry in

the magnetic switch points of the device. For irregular

tooth geometry, there will a small but noticeable change in

pulse width versus air gap.

* Target must be rotating for proper update algorithim

operation.

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