True Zero-Speed Low-Jitter High Accuracy
Gear Tooth Sensor IC
ATS625LSG
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Device Description
Figure 2. Device Cross Section. Relative motion of the target is detected
by the dual Hall elements mounted on the Hall IC. This view is from the
side opposite the pins.
Figure 3. 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 centered
over the face of the package. A right-to-left (pin 4 to pin 1) rotation inverts
the output signal polarity.
Target (Gear)
Back-biasing
Rare Earth Pellet
South Pole
North Pole
Plastic
(Pin 1 Side)
(Pin n >1 Side)
Hall IC
Pole Piece
Element Pitch
(Concentrator)
Dual-Element
Hall Effect Device
Hall Element 1
Hall Element 2
of Package
Rotating Target
Branded Face
1
4
Package Description
The ATS625LSG is a combined Hall IC and rare-earth pellet
configuration that is fully optimized to provide digital detec-
tion of gear tooth edges. This device is integrally molded into a
plastic body that has been optimized for size, ease of assembly,
and manufacturability. High operating temperature materials are
used in all aspects of construction.
Hall Technology
The ATS625 contains a single-chip differential Hall effect sen-
sor IC, a 4-pin leadframe, a samarium cobalt pellet, and a flat
ferrous pole piece. The Hall IC consists of two Hall elements
spaced 2.2 mm apart, and each independently measures the
magnetic gradient created by the passing of a ferrous object. This
is illustrated in figures 2 and 3. The differential output of the
two elements is converted to a digital signal that is processed to
provide the digital output.
Switching Description
After proper power is applied to the component, the chip is then
capable of providing digital information that is representative of
the profile of a rotating gear, as illustrated in figure 4. No addi-
tional optimization is needed and minimal processing circuitry is
required. This ease of use reduces design time and incremental
assembly costs for most applications.
Figure 4. The magnetic profile reflects the geometry of the target, allowing the device to present an accurate digital output response.
Target
Mechanical Profile
Target
Magnetic Profile
IC Output
Electrical Profile
Target Motion from
Pin 1 to Pin 4
IC Output
Electrical Profile
Target Motion from
Pin 4 to Pin 1
Signature Tooth
B+
B
IN
V+
V
OUT
V+
V
OUT
IC Output
Switch State
On Off On Off On Off On Off
On Off
On Off
On Off
On    Off