AATS643LSH_06 Datasheet, PDF (9/16 Pages) Allegro MicroSystems – Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update

ATS643LSH
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
Functional Description
Sensing Technology. The ATS643 module contains a
single-chip differential Hall effect sensor IC, a samarium cobalt
magnet, and a flat ferrous pole piece (concentrator). As shown
in figure 1, the Hall IC supports two Hall elements, which sense
the magnetic profile of the ferrous gear target simultaneously,
but at different points (spaced at a 2.2 mm pitch), generating a
differential internal analog voltage (V_PROC) that is processed for
precise switching of the digital output signal.
The Hall IC is self-calibrating and also possesses a tempera-
ture compensated amplifier and offset cancellation circuitry. Its
voltage regulator provides supply noise rejection throughout the
operating voltage range. Changes in temperature do not greatly
affect this device due to the stable amplifier design and the offset
rejection circuitry. The Hall transducers and signal processing
electronics are integrated on the same silicon substrate, using a
proprietary BiCMOS process.
Target Profiling During Operation. When proper power is
applied to the sensor, it is capable of providing digital informa-
tion that is representative of the mechanical features of a rotating
gear. The waveform diagram in figure 3 presents the automatic
translation of the mechanical profile, through the magnetic
profile that it induces, to the digital output signal of the ATS643.
No additional optimization is needed and minimal processing
circuitry is required. This ease of use reduces design time and
incremental assembly costs for most applications.
Determining Output Signal Polarity. In figure 3, the top
panel, labeled Mechanical Position, represents the mechani-
cal features of the target gear and orientation to the device. The
bottom panel, labeled Sensor Output Signal, displays the square
waveform corresponding to the digital output signal that results
from a rotating gear configured as shown in figure 2. That direc-
tion of rotation (of the gear side adjacent to the face of the sensor)
is: perpendicular to the leads, across the face of the device, from
the pin 1 side to the pin 4 side. This results in the sensor output
switching from low, I_CC(Low), to high, I_CC(High), as the leading
edge of a tooth (a rising mechanical edge, as detected by the
sensor) passes the sensor face. In this configuration, the device
output current switches to its high polarity when a tooth is the
target feature nearest to the sensor. If the direction of rotation is
reversed, so that the gear rotates from the pin 4 side to the pin 1
side, then the output polarity inverts. That is, the output signal
goes high when a falling edge is detected, and a valley is the
nearest to the sensor. Note, however, that the polarity of I_OUT
depends on the position of the sense resistor, R_SENSE (see Operat-
ing Characteristics table).
Continuous Update of Switchpoints. Switchpoints are the
threshold levels of the differential internal analog signal, V_PROC,
at which the device changes output signal polarity. The value of
Target (Gear)
Hall Element 2
Dual-Element
Hall Effect Device
(Pin n >1 Side)
South Pole
North Pole
Element Pitch
Hall Element 1
Hall IC
Pole Piece
(Concentrator)
Back-biasing Magnet
Case
(Pin 1 Side)
Figure 1. Relative motion of the target is detected by the dual Hall ele-
ments mounted on the Hall IC.
Rotating Target
Branded Face
of Sensor
14
Figure 2. 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 face of the sensor (see figure 3). A right-to-left (pin 4 to pin 1) rota-
tion inverts the output signal polarity.
Mechanical Position (Target movement pin 1 to pin 4)
This tooth
sensed
earlier
Target
(Gear)
This tooth
sensed
later
Target Magnetic Profile
+B
Sensor Orientation to Target
Pin 4
Side
Sensor Branded Face
Sensor
Pin 1
Side
Sensor Internal Differential Analog Signal, V_PROC
B_OP(#1)
B_OP(#2)
+t
B_RP(#1)
Sensor Internal Switch State
Off
On
Off
On
+t
Sensor Output Signal, I_OUT
+t
Figure 3. The magnetic profile reflects the geometry of the target, allow-
ing the ATS643 to present an accurate digital output response.
Allegro MicroSystems, Inc.
9
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com