Self-Calibrating TPOS Speed Sensor IC

Optimized for Automotive Cam Sensing Applications

ATS675LSE

12

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Target

Mechanical

Profile

0

Time

|B|

100

0

Application and internal baseline

Running Mode Operation

Running mode begins immediately at the end of Calibration

mode. During Running mode, switchpoints are established

dynamically, based on the sensed application magnetic gradi-

AGC feature, and processed to generate the internal processed

form, and the output switchpoints are established as percentages

of the values held by the two DACs. Because the switchpoints

are established dynamically as a percentage of the peak-to-peak

signal, the effects of an application baseline shift are minimized.

Running Mode Switchpoints

The values used to define Running mode switchpoints are cal-

that is, at the most prominent target tooth. On the ATS675LSE,

the switchpoints are referenced to approximately 30% of the

peak-to-peak magnetic signal. This level closely corresponds to

the mechanical target edges, resulting in optimal timing accuracy

versus air gap.

Running Mode Hysteresis

The ATS675LSE uses an internal hysteresis method, switching at

a consistent point on both rising and falling edges. When a target

anomaly is encountered, the internal hysteresis thresholds provide

immunity to false switching, as illustrated in figure 12.

Figure 11. Switchpoints Level for Running Mode definition

(switchpoints indicated by circles).

Figure 12. Running mode switching on anomalous peak

(switchpoints indicated by circles).

Time

Switchpoints Level

On

Output State

for LT option

Off

On

Off