ATS642LSH Datasheet, PDF (11/16 Pages) Allegro MicroSystems – Two-Wire True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor with Continuous Calibration

ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
Automatic Gain Control (AGC)
This feature allows the device to operate with an optimal internal
electrical signal, regardless of the air gap (within the AG speci-
fication). During calibration, the device determines the peak-to-
peak amplitude of the signal generated by the target. The gain of
the sensor is then automatically adjusted. Figure 5 illustrates the
effect of this feature.
Automatic Offset Adjust (AOA)
The AOA is patented circuitry that automatically compensates
for the effects of chip, magnet, and installation offsets. (For
capability, see Dynamic Offset Cancellation, in the Operat-
ing Characteristics table.) This circuitry is continuously active,
including both during calibration mode and running mode, com-
pensating for any offset drift. Continuous operation also allows it
to compensate for offsets induced by temperature variations over
time.
Digital Peak Detection
A digital DAC tracks the internal analog voltage signal V_PROC,
and is used for holding the peak value of the internal analog
signal. In the example shown in figure 6, the DAC would first
track up with the signal and hold the upper peak’s value. When
V_PROC drops below this peak value by B_OP, the device hyster-
esis, the output would switch and the DAC would begin tracking
the signal downward toward the negative V_PROC peak. Once the
DAC acquires the negative peak, the output will again switch
states when V_PROC is greater than the peak by the value B_RP. At
this point, the DAC tracks up again and the cycle repeats. The
digital tracking of the differential analog signal allows the sensor
to achieve true zero-speed operation.
Ferrous Target
Mechanical Profile
V+
Internal Differential
Analog Signal
Response, without AGC
V+
Internal Differential
Analog Signal
Response, with AGC
AG_Large
AG_Small
AG_Small
AG_Large
V+
Internal
Differential
Analog Signal
I+
Device
Output Current
B_OP
B_RP
Figure 5. Automatic Gain Control (AGC). The AGC function corrects for
variances in the air gap. Differences in the air gap affect the magnetic
gradient, but AGC prevents that from affecting device performance, a
shown in the lowest panel.
Figure 6: Peak Detecting Switchpoint Detail
ATS642LSH-DS
Allegro MicroSystems, Inc.
11
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com