ATS645 Allegro MicroSystems, Inc., ATS645 Datasheet - Page 9

• Manufacturer Part Number: ATS645
• Description: Ats645lsh True Zero Speed Miniature Gear-tooth Sensors
• Manufacturer: Allegro MicroSystems, Inc.

Response, without AGC
ATS645LSH
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-
fi cation). 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 cancels the
effects of chip, magnet, and installation offsets. (For capability,
see Dynamic Offset Cancellation, in the Operating Characteris-
tics table.) This circuitry is continuously active, including both
during calibration mode and running mode, compensating for
any offset drift. Continuous operation also allows it to compen-
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.
Response, with AGC
Internal Differential
Internal Differential
Mechanical Profile
Ferrous Target
Analog Signal
Analog Signal
V+
V+
True Zero Speed Miniature Differential Peak-
AG
AG
AG
AG
Large
Small
Small
Large
sate for offsets induced by temperature variations over time.
Digital Peak Detection
A digital DAC tracks the internal analog voltage signal V
and is used for holding the peak value of the internal analog
signal. In the example shown in fi gure 6, the DAC would fi rst
track up with the signal and hold the upper peak’s value. When
V
esis, the output would switch and the DAC would begin tracking
the signal downward toward the negative V
DAC acquires the negative peak, the output will again switch
states when V
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.
Figure 6: Peak Detecting Switchpoint Detail
PROC
Internal
Differential
Analog Signal
Device
Output Current
Detecting Gear Tooth Sensor
drops below this peak value by B
PROC
V+
I+
is greater than the peak by the value B
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
B
OP
OP
, the device hyster-
PROC
peak. Once the
B
RP
PROC
RP
. At
,
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