ATS645 Allegro MicroSystems, Inc., ATS645 Datasheet - Page 8

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

ATS645LSH
Figure 1. Relative motion of the target is detected by the dual Hall ele-
ments mounted on the Hall IC.
Figure 2. This left-to-right (pin 1 to pin 4) direction of target rotation
results in a low output signal when a tooth of the target gear is nearest
the face of the sensor (see fi gure 3). A right-to-left (pin 4 to pin 1) rota-
tion inverts the output signal polarity.
Sensing Technology
The gear tooth sensor subassembly contains a single-chip dif-
ferential Hall effect sensor IC, an optimized samarium cobalt
magnet, and a fl at ferrous pole piece. The Hall IC supports two
Hall elements, which sense the magnetic profi le of the ferrous
target simultaneously, but at different points (spaced at a 1.5 mm
pitch), generating a differential internal analog voltage (V
that is processed for precise switching of the digital output
signal.
The Hall IC is self-calibrating and also possesses a tempera-
ture compensated amplifi er 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 amplifi er 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
An operating device is capable of providing digital information
that is representative of the mechanical features on a rotating tar-
get. The waveform diagram shown in fi gure 3 presents the auto-
matic translation of the mechanical profi le, through the magnetic
profi le that it induces, to the digital output signal of the sensor.
Hall Effect Device
Hall Element 2
Dual-Element
Target (Gear)
Rotating Target
(Pin 4 Side)
South Pole
North Pole
1
4
True Zero Speed Miniature Differential Peak-
(Pin 1 Side)
(Concentrator)
Element Pitch
Hall Element 1
Hall IC
Pole Piece
Back-biasing Magnet
Case
Branded Face
of Sensor
Functional Description
PROC
)
Output Polarity
Figure 3 shows the output polarity for the orientation of target
and sensor shown in fi gure 2. The target direction of rotation
shown 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 high, I
the leading edge of a tooth (a rising mechanical edge, as detected
by the sensor) passes the sensor face. In this confi guration, the
device output current switches to its low polarity when a tooth is
the target feature nearest to the sensor. If the direction of rota-
tion is reversed, then the output polarity inverts.
Note that output voltage polarity is dependent on the position of
the sense resistor, R
Figure 3. Output Profi le of a ferrous target for the polarity indicated in
fi gure 2.
Figure 4: Voltages profi les for high side and low side two-wire sensing.
Target
Mechanical Profile
Representative
Differential
Magnetic Profile
Sensor Electrical
Output Profile, I
Detecting Gear Tooth Sensor
I
V
V
OUT
OUT(L)
OUT(H)
I+
V+
V+
OUT
SENSE
ATS645
GND
VCC
4
1
V
CC
(see fi gure 4).
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
V
R
I
OUT(L)
CC
SENSE
CC(High)
ATS645
GND
VCC
4
1
, to low I
V
CC
R
V
I
CC
OUT(H)
SENSE
CC(Low)
, as
8