3064
HALL-EFFECT GEAR-TOOTH SENSOR
—AC COUPLED
The A3064LKA ac-coupled Hall-effect gear-tooth sensor is a
monolithic integrated circuit that switches in response to changing
differential magnetic fields created by moving ferrous targets. This
device is ideal for use in non-zero-speed, gear-tooth-based speed,
position, and timing applications such as in anti-lock braking systems,
transmissions, and crankshafts.
When coupled with a back-biasing magnet, the sensor can be
configured to turn on or off with the leading or trailing edge of a gear-
tooth or slot. Changes in fields on the magnet face caused by a moving
ferrous mass are sensed by two integrated Hall transducers and are
differentially amplified by on-chip electronics. This differential
sensing design provides immunity to radial vibration within the
device’s operating air gap. Steady-state magnet and system offsets are
eliminated using an on-chip differential band-pass filter. This filter
also provides relative immunity to interference from RF and electro-
magnetic sources. The on-chip temperature compensation and Schmitt
trigger circuitry minimizes shifts in effective working air gaps and
switch points over temperature, allowing operation to low frequencies
over a wide range of air gaps and temperatures.
Each Hall-effect digital Integrated circuit includes a voltage
regulator, two quadratic Hall-effect sensing elements, temperature
compensating circuitry, a low-level amplifier, band-pass filter, Schmitt
trigger, and an open-collector output driver. The on-board regulator
permits operation with supply voltages of 4.5 to 24 volts. The output
stage can easily switch 20 mA over the full frequency response range
of the sensor and is compatible with bipolar and MOS logic circuits.
The device is packaged in a 5-pin plastic SIP.
Data Sheet
27612.21
X
X
VCC
1
2
3
4
5
GROUND
FILTER
SUPPLY
OUTPUT
Dwg. PH-011-1
Pinning is shown viewed from branded side.
ABSOLUTE MAXIMUM RATINGS
at T
A
= +25
°
C
Supply Voltage, V
CC
.............................
24 V
Reverse Battery Voltage, V
RCC
..........
-30 V
Magnetic Flux Density, B ............
Unlimited
Output Off Voltage, V
OUT
......................
24 V
Output Current, I
OUT
.........................
25 mA
Package Power Dissipation,
P
D
............................................
500 mW
Operating Temperature Range,
T
A
...............................
-40
°
C to +150
°
C
Storage Temperature Range,
T
S
...............................
-65
°
C to +170
°
C
FILTER
FEATURES
s
s
s
s
s
s
s
s
s
Senses Motion of Ferrous Targets
Wide Operating Temperature Range
Operation to 30 kHz
Resistant to EMI
Large Effective Air Gap
4.5 V to 24 V Operation
Output Compatible With All Logic Families
Reverse Battery Protection
Resistant to Physical Stress
Always order by complete part number, e.g.,
A3064LKA
.
3064
HALL-EFFECT
GEAR-TOOTH SENSOR
—AC COUPLED
1
SUPPLY
FUNCTIONAL BLOCK DIAGRAM
REG
OUTPUT
2
+
-
X
X
4
FILTER
5
FILTER
3
GROUND
Dwg. FH-008-1
ELECTRICAL CHARACTERISTICS over operating temperature and supply voltage range.
Limits
Characteristic
Supply Voltage
Output Saturation Voltage
Output Leakage Current
Supply Current
Symbol
V
CC
V
OUT(SAT)
I
OFF
I
CC
f
coh
t
r
t
f
Test Conditions
Operating
I
OUT
= 18 mA, B < B
RP
V
OUT
= 24 V, B > B
OP
B < B
RP
B > B
OP
High-Frequency Cutoff
Output Rise time
Output Fall time
-3 dB
V
OUT
= 12 V, R
L
= 820
Ω
V
OUT
= 12 V, R
L
= 820
Ω
Min.
4.5
—
—
—
—
30
—
—
Typ.
—
141
—
11
9.6
—
0.04
0.18
Max.
24
400
5.0
20
—
—
0.2
0.3
Units
V
mV
µA
mA
mA
kHz
µs
µs
MAGNETIC CHARACTERISTICS over operating temperature and supply voltage range.
Limits
Characteristic
Operate Point
Release Point
Hysteresis
Symbol
B
OP
B
RP
B
hys
Test Conditions
Output switches on to off
Output switches off to on
B
OP
- B
RP
Min.
0
-12.5
5.0
Typ.
15
0
15
Max.
27.5
7.5
35
Units
G
G
G
NOTES: 1. Magnetic switch points are specified as the difference in magnetic fields at the two Hall elements.
2. As used here, negative flux densities are defined as less than zero (algebraic convention).
3. Typical values are at T
A
= 25°C and V
CC
= 12 V.
4. 1 gauss (G) is exactly equal to 0.1 millitesla (mT).
2
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 2001 Allegro MicroSystems, Inc.
3064
HALL-EFFECT
GEAR-TOOTH SENSOR
—AC COUPLED
TYPICAL OPERATING CHARACTERISTICS
SWITCH POINTS
30
V
CC
= 12 V
DIFFERENTIAL FLUX DENSITY IN GAUSS
20
OPERATE POINT
10
0
RELEASE POINT
-10
-50
-25
0
25
50
75
100
125
150
AMBIENT TEMPERATURE IN
°C
Dwg. GH-056-1
OUTPUT SATURATION VOLTAGE
300
200
I
OUT
= 18 mA
V
CC
= 12 V
I
OUT
= 18 mA
T
A
= +25°C
SATURATION VOLTAGE IN mV
200
SATURATION VOLTAGE IN mV
150
100
100
0
-50
50
-25
0
25
50
75
100
125
150
0
5
10
15
20
25
AMBIENT TEMPERATURE IN
°C
Dwg. GH-029-6
SUPPLY VOLTAGE IN VOLTS
Dwg. GH-055-2
www.allegromicro.com
3
3064
HALL-EFFECT
GEAR-TOOTH SENSOR
—AC COUPLED
TYPICAL OPERATING CHARACTERISTICS
SUPPLY CURRENT
20
V
CC
= 24 V
20
15
15
SUPPLY CURRENT IN mA
SUPPLY CURRENT IN mA
B < B
RP
B < B
RP
10
B > B
OP
10
B > B
OP
5
5
T
A
= +25°C
0
-50
0
-25
0
25
50
75
100
125
150
0
5
10
15
20
25
AMBIENT TEMPERATURE IN
°C
Dwg. GH-028-9
SUPPLY VOLTAGE IN VOLTS
Dwg. GH-031-3
APPLICATIONS INFORMATION
The A3064LKA is a versatile high-precision differential
sensing device that can be used in a wide range of applications.
Careful choice of the sensor IC, target material and shape,
magnet material and shape, and assembly techniques enables
large working air gaps and high switch-point accuracy over the
system operating temperature range.
Magnet Biasing.
To sense moving non-magnetized
ferrous targets, these devices must be back biased by mounting
the unbranded side on a small permanent magnet. Either
magnetic pole (north or south) can be used.
The devices can be used without a back-biasing magnet.
For example, the sensor can be used to detect a rotating ring
magnet such as those found in brushless dc motors or in speed
sensing applications.
Sensor Operation.
These sensor ICs each contain two
integrated Hall transducers (E1 and E2) that are used to sense a
magnetic field differential across the face of the IC (see Sensor
Location drawing). Referring to the Typical Transfer Charac-
teristic (Figure 1), the trigger switches the output off (output
high) when B
E1
- B
E2
> B
OP
and switches the output on (output
Figure 1
TYPICAL TRANSFER CHARACTERISTIC
+V
V
CC
OUTPUT VOLTAGE
B
RP
B
OP
V
OUT(SAT)
0
-B
0
FLUX DENSITY
+B
Dwg. GH-007-6
4
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
3064
HALL-EFFECT
GEAR-TOOTH SENSOR
—AC COUPLED
APPLICATIONS INFORMATION (cont’d)
low) when B
E1
- B
E2
< B
RP
. The difference between B
OP
and
B
RP
is the hysteresis of the device.
Note that powering up in the absence of a differential
magnetic field (less than the device B
OP
and higher than the
device B
RP
) will allow an indeterminate output state. The
correct output state is warranted after the first excursion beyond
B
OP
or B
RP
.
Figure 2 relates the output state of a back-biased sensor IC,
with switching characteristics shown in Figure 1, to the target
gear profile and position. Assume a north pole back-bias
configuration (equivalent to a south pole at the face of the
device). The motion of the gear produces a phase-shifted field
at E1 and E2 (Figure 2(a)); internal conditioning circuitry
subtracts the fields at the two elements (Figure 2(b)); this
differential field is band-pass filtered to remove dc offset
components and then fed into a Schmitt trigger; the Schmitt
trigger switches the output transistor at the thresholds B
OP
and
B
RP
. As shown (Figure 2(c)), the IC output is low whenever
sensor E2 faces a (ferrous) gear tooth and sensor E1 faces air.
The output is high when sensor E1 faces air and sensor E2 faces
a ferrous target.
AC-Coupled Operation.
Steady-state magnet and
system offsets are eliminated using an on-chip differential band-
pass filter. The lower frequency cut-off of this patented filter is
set using an external capacitor, the value of which can range
from 0.01
µF
to 10
µF.
The high-frequency cut-off of this filter
is set at 30 kHz by an internal integrated capacitor.
The differential structure of this filter improves the ability
of the IC to reject single-ended noise on the ground or supply
line and, as a result, makes it more resistant to radio-frequency
and electromagnetic interference typically seen in hostile
remote-sensing environments. This filter configuration also
increases system tolerance to capacitor degradation at high
temperatures, allowing the use of an inexpensive external
ceramic capacitor.
Low-Frequency Operation.
Low-frequency operation
of the sensor is set by the value of an external capacitor.
Ideally, the differential flux density range (determined by the
applied target) vs. air gap assumes a perfect sinusoidal input.
Figure 3 provides the low-frequency cut-off (-3 dB point) of the
filter as a function of capacitance value. This information
should be used with care. In reality, when used with gear teeth,
4300 G
Figure 2
LEADING
EDGE
TRAILING
EDGE
GEAR
DIRECTION
OF ROTATION
E2
NORTH
E1
SOUTH
B &B
E1
E2
(a)
4150 G
150 G
B
OP
= +15 G
(b)
B –B
E1
E2
0G
B
RP
= 0 G
-150 G
V
OUT
(c)
V
OUT(SAT)
OUTPUT DUTY CYCLE
≈
50%
Dwg. WH-003-3
Figure 3
1k
100
LOW-FREQUENCY CUTOFF IN Hz
10
1.0
0.1
0.01
0.1
1.0
10
CAPACITANCE IN
µF
Dwg. GH-025
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