Self-Calibrating TPOS Gear Tooth Sensor Optimized

for Automotive Cam Sensing Applications

ATS673 and

ATS674

13

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

B

HYS

B

HYS

B

HYS

B

HYS

t+

V+

B

HYS

B

HYS

B

HYS

B

HYS

(A) TEAG varying; cases such as

eccentric mount, out-of-round region,

normal operation position shift

typically resulting in the sensor

0

360

Target Rotation (°)

Hysteresis Band

(Delimited by switchpoints)

V+

Larger

TEAG

Smaller

TEAG

Sensor

Target

Larger

TEAG

Target

Sensor

Smaller

TEAG

Smaller

TEAG

Figure 9. The Continuous Update algorithm allows the Allegro sensor to immediately interpret and adapt to significant 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). The algorithm is used to dynamically establish and subsequently

As shown in panel A, the variance in the target position results in a change in the TEAG. This affects the sensor as a varying magnetic field, which

Switchpoint

Determinant

Peak Values

Update

The ATS673 and ATS674 incorporate an algorithm that continu-

ously monitors the system and updates the switching thresholds

accordingly. The switchpoint for each transition is determined

by the previous two transitions. Because variations are tracked

in real time, the sensor has high immunity to target run-out and

retains excellent accuracy and functionality in the presence of

both run-out and transient mechanical events. Figure 9 shows

how the devices use historical data to provide the switching

thresholds for a given edge.