ATS675LSETN-HT-T Allegro, ATS675LSETN-HT-T Datasheet - Page 10

• Manufacturer Part Number: ATS675LSETN-HT-T
• Manufacturer: Allegro

ATS675LSE
TPOS (True Power-On State) Operation
Under specified operating conditions, the ATS675 is guaranteed
to attain the specified output voltage polarity at power-on, in
relation to the target feature nearest the device at that time. The
TPOS switchpoint is programmed by Allegro to the datasheet
specifications.
Start-Up Detection
The ATS675 provides an output polarity transition at the first
target mechanical edge that is opposite the device after power-on.
Calibration
The Automatic Gain Calibration (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,
V
the device. This feature ensures that operational characteristics
are isolated from the effects of changes in effective air gap. The
Initial Calibration process allows the peak detecting DACs to
properly acquire the magnetic signal, so that a Running Mode
switchpoint can be accurately computed.
TPOS to Running Mode
After the Initial Calibration process is completed (CAL
device transitions to Running Mode. As shown in figure 9, on the
first edge after CAL
Figure 9. Startup calibration order
PROC
Output state for
LT option polarity
, at a constant amplitude throughout the air gap range of
TPOS
Threshold
I
, the device immediately transitions from
Off
CAL
On
I
(
p
Running Mode
)
Optimized for Automotive Cam Sensing Applications
Running
Mode, B
ST
I
), the
Self-Calibrating TPOS Speed Sensor
TPOS to Running Mode switching thresholds. This can result
in a single jump in output edge position, measurable as a timing
accuracy error.
Switchpoints
The Running Mode switchpoints in the ATS675 are established
dynamically as a percentage of the amplitude of the signal,
V
peaks of V
The switching threshold is established at a fixed percentage of the
values held in the two DACs. The ATS675 uses a single switch-
ing threshold (operate and release points identical) with internal
hysteresis.
Internal Hysteresis
The Internal Hysteresis, B
various air gaps while maintaining immunity to false switching
on noise, vibration, backlash, or other transient events. Figure 10
demonstrates the function of this hysteresis when switching on an
anomalous peak.
Peak and Valley DAC Update
The peak and valley DACs have an algorithm that allows track-
ing of drift over temperature changes, but provides immunity to
target particularities, such as small mechanical valleys.
Figure 10. Output switching can accommodate an anomalous peak, such
as the middle peak in this figure, by using the Internal Hysteresis value.
PROC
Switch State
Switch State
LT option
HT option
, after normalization with AGC. Two DACs track the
PROC
V
V
OUT
OUT
.
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HYS
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
B
, provides high performance over
ST
B
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0n
HYS
B
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