ATS616 Datasheet, PDF (11/14 Pages) Allegro MicroSystems – Dynamic Self-Calibrating Peak-Detecting Differential Hall Effect Gear Tooth Sensor

ATS616LSG
Dynamic Self-Calibrating Peak-Detecting Differential
Hall Effect Gear Tooth Sensor IC
(normal AC coupling) is a commonly used technique for elimi-
nating circuit offsets. However, AC coupling has errors at power-
on because the filter circuit needs to hold the circuit zero value
even though the circuit may power-on over a large signal. Such
filtering techniques can only perform properly after the filter
has been allowed to settle, which typically takes longer than 1s.
Also, high-pass filter solutions cannot easily track rapidly chang-
ing baselines, such as those caused by eccentricities. (The term
baseline refers to a 0 G differential field, where each Hall-effect
element is subject to the same magnetic field strength; see figure
3.) In contrast, peak detecting designs switch at the change in
slope of the differential signal, and so are baseline-independent
both at power-on and while running.
Peak Detecting vs. Zero-Crossing Reference. The usual dif-
ferential zero-crossing sensor ICs are susceptible to false switch-
ing due to off-center and tilted installations that result in a shift
of the baseline that changes with air gap. The track-and-hold
peak detection technique ignores baseline shifts versus air gaps
and provides increased immunity to false switching. In addition,
using track-and-hold peak detection techniques, increased air
gap capabilities can be expected because peak detection utilizes
the entire peak-to-peak signal range, as compared to zero-cross-
ing detectors, which switch at half the peak-to-peak signal.
Power-On Operation. The device powers-on in the Off state
(output voltage high), irrespective of the magnetic field condi-
tion. The power-up time of the circuit is no greater than 500 μs.
The circuit is then ready to accurately detect the first target edge
that results in a high-to-low transition of the device output.
Undervoltage Lockout (UVLO). When the supply voltage, V_CC ,
is below the minimum operating voltage, V_CC(UV) , the device is
off and stays off, irrespective of the state of the magnetic field.
This prevents false signals, which may be caused by undervolt-
age conditions (especially during power-up), from appearing at
the output.
Output. The device output is an open-collector stage capable of
sinking up to 20 mA. An external pull-up (resistor) must be sup-
plied to a supply voltage of not more than 24 V.
Output Polarity. The output of the unit will switch from low to
high as the leading edge of a tooth passes the branded face of the
package in the direction indicated in figure 6. This means that in
such a configuration, the output voltage will be high when the
package is facing a tooth. If the target rotation is in the oppo-
site direction relative to the package, the output polarity will be
opposite as well, with the unit switching from low to high as the
leading edge passes the unit.
Rotating Target
Branded Face
of Package
14
Figure 6. This left-to-right (pin 1 to pin 4) direction of target rotation
results in a high output signal when a tooth of the target gear is nearest
the branded face of the package. A right-to-left (pin 4 to pin 1) rotation
inverts the output signal polarity.
Target
Mechanical Profile
Target
B+
Magnetic Profile
B_IN
Signature Tooth
IC Output
Switch State
On Off On Off On Off On Off On
Off
IC Output
Electrical Profile
Target Motion from
Pin 1 to Pin 4
IC Output
Electrical Profile
Target Motion from
Pin 4 to Pin 1
V+
V_OUT
V+
V_OUT
On Off On Off On Off
Figure 7. The magnetic profile reflects the geometry of the target, allowing the device to present an accurate digital output response.
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