ATS625LSG Datasheet, PDF (13/21 Pages) Allegro MicroSystems – True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor

ATS625LSG
True Zero-Speed Low-Jitter High Accuracy
Gear Tooth Sensor
AGC (Automatic Gain Control)
The AGC feature is implemented by a unique patented self-
calibrating circuitry. After each power-on, the device measures
the peak-to-peak magnetic signal. The gain of the sensor is then
adjusted, keeping the internal signal amplitude constant over the
air gap range of the device, AG. This feature ensures that opera-
tional characteristics are isolated from the effects of changes in
AG. The effect of AGC is shown in figure 7.
Differential Electrical Signal versus Target Rotation
at Various Air Gaps, Without AGC
1000
800
600
400
200
AG:
0.25 mm
0.50 mm
1.00 mm
1.50 mm
2.00 mm
0
-200
-400
-600
-800
-1000
0
3
6
9 12 15 18 21 24
Target Rotation (°)
Differential Electrical Signal versus Target Rotation
at Various Air Gaps, With AGC
1000
800
600
400
AG:
0.25 mm
0.50 mm
1.00 mm
1.50 mm
2.00 mm
200
0
-200
-400
-600
-800
-1000
0
3
6
9 12 15 18 21 24
Target Rotation (°)
Figure 7. Effect of AGC. The left panel shows the process signal, V_PROC, without AGC. The right panel shows the effect with
AGC. The result is a normalized V_PROC, which allows optimal performance by the rest of the circuits that reference this signal.
Offset Adjustment
In addition to normalizing performance over varying AG, the
gain control circuitry also reduces the effect of chip, magnet,
and installation offsets. This is accomplished using two DACs
(D to A converters) that capture the peaks and valleys of the
processed signal, V_PROC, and use it as a reference for the Thresh-
old Comparator subcircuit, which controls device switching. If
induced offsets bias the absolute signal up or down, AGC and
the dynamic DAC behavior work to normalize and reduce the
impact of the offset on sensor performance.
Allegro MicroSystems, Inc.
13
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com