ATS622LSB

TRUE ZERO-SPEED,

GEAR-TOOTH SENSOR

9

www.allegromicro.com

APPLICATIONS INFORMATION — Continued

Dwg. MH-018-5 mm

A

2.2

α

TARGET FACE WIDTH, F

>2.2 SIN

α

Recommended evaluation technique. The self-

calibrating feature of the ATS622LSB requires that a

special evaluation technique be used to measure its high-

accuracy performance capabilities. Installation inaccura-

cies are calibrated out at power on; hence, it is extremely

important that the device be repowered at each air gap

when gathering timing accuracy data.

The ATS622LSB is designed to minimize performance

variation (caused by the large air-gap variations resulting

from installation) by self-calibrating at power-on. These

functions should be tested using the procedures described

below.

Timing accuracy capabilities after correct self-calibra-

tion can be measured as follows:

1. Set the air gap to the desired value.

2. Power down and then power up the device.

3. Rotate the gear at the desired speed.

4. Wait for calibration to complete (128 output pulses to

occur).

5. Monitor output for correct switching and measure

accuracy.

6. Repeat the above for multiple air gaps within the

operating range of the device.

7. This can be repeated over the entire operating tem-

perature range.

There is an internal update algorithm that will maintain

the correct duty cycle as air gap changes with temperature.

Large changes in air gap will require the part to reset (by

cycling power) to maintain the correct duty cycle.

Measurement of the effect of changing air gap after

power up:

1. Set the air gap to the desired value (nominal, for

example). Rotate the target at the desired speed. Apply

power to the module. Wait for 128 output pulses to occur.

Monitor output for correct switching and measure accu-

racy.

2. Change the air gap by

±0.25 mm. Do not re-power the

module. Wait for update algorithm to finish adjusting

thresholds, typically 2 to 3 rotations on a 60-tooth gear.

Operation with fine-pitch gears. For targets with a

circular pitch of less than 4mm, a performance improve-

ment can be observed by rotating the front face of the

sensor. This sensor rotation decreases the effective

sensor-to-sensor spacing and increases the capability of

detecting fine tooth or valley configurations, provided that

the Hall elements are not rotated beyond the width of the

target.