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use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
AD22151
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
Analog Devices, Inc., 1997
Linear Output
Magnetic Field Sensor
FUNCTIONAL BLOCK DIAGRAM
TEMP REF
I
SOURCE
DEMOD
SWITCHES
OUT AMP
REF
V
CC
/2
AD22151
FEATURES
Adjustable Offset to Unipolar or Bipolar Operation
Low Offset Drift Over Temperature Range
Gain Adjustable Over Wide Range
Low Gain Drift Over Temperature Range
Adjustable First Order Temperature Compensation
Ratiometric to V
CC
APPLICATIONS
Automotive
Throttle Position Sensing
Pedal Position Sensing
Suspension Position Sensing
Valve Position Sensing
Industrial
Absolute Position Sensing
Proximity Sensing
GENERAL DESCRIPTION
The AD22151 is a linear magnetic field transducer. The sensor
output is a voltage proportional to a magnetic field applied
perpendicularly to the package top surface.
The sensor combines integrated bulk Hall cell technology and
instrumentation circuitry to minimize temperature related drifts
associated with silicon Hall cell characteristics. The architecture
maximizes the advantages of a monolithic implementation while
allowing sufficient versatility to meet varied application require-
ments with a minimum number of components.
Principle features include dynamic offset drift cancellation and a
built-in temperature sensor. Designed for single +5 volt supply
operation, the AD22151 achieves low drift offset and gain op-
eration over 40
C to +150
C. Temperature compensation can
accommodate a number of magnetic materials commonly uti-
lized in economic position sensor assemblies.
The transducer may be configured for specific signal gains de-
pendent upon application requirements. Output voltage can be
adjusted from fully bipolar (reversible) field operation to fully
unipolar field sensing.
The voltage output achieves near rail-to-rail dynamic range,
capable of supplying 1 mA into large capacitive loads. The sig-
nal is ratiometric to the positive supply rail in all configurations.
NC
R1
GND
R3
R2
V
CC
AD22151
NC = NO CONNECT
OUTPUT
0.1 F
Figure 1. Typical Bipolar Configuration with Low
(< 500 ppm) Compensation
NC
R1
GND
R3
R2
V
CC
AD22151
NC = NO CONNECT
OUTPUT
0.1 F
R4
Figure 2. Typical Unipolar Configuration with High
(
2000 ppm) Compensation
2
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AD22151SPECIFICATIONS
(T
A
= +25 C and V+ = +5 V unless otherwise noted)
Parameters
Min
Typ
Max
Units
OPERATION
V
CC
Operating
4.5
5.0
6.0
V
I
CC
Operating
6.0
10
mA
INPUT
TC3 (Pin 3) Sensitivity/Volt
160
V/G/V
Input Range
1
V
CC
2
0.5
V
OUTPUT
2
Sensitivity (External Adjustment, Gain = 1)
0.4
mV/G
Linear Output Range
10
90
% of V
CC
Output Min
5
% of V
CC
Output Max (Clamp)
93
% of V
CC
Drive Capability
1.0
mA
Offset @ 0 Gauss
V
CC
2
V
Offset Adjust Range
5
95
% of V
CC
Output Short Circuit Current
5.0
mA
ACCURACIES
Nonlinearity (10% to 90% Range)
0.1
% FS
Gain Error (Over Temperature Range)
1
%
Offset Error (Over Temperature Range)
6.0
G
Uncompensated Gain TC (G
TCU
)
950
ppm
RATIOMETRICITY ERROR
1
%V/V
CC
3 dB ROLL-OFF (5 mV/G)
5.7
kHz
OUTPUT NOISE FIGURE (6 kHz BW)
2.4
mV/rms
PACKAGE
8-Lead SOIC
OPERATING TEMPERATURE RANGE
40
+150
C
NOTES
1
40
C to +150
C.
2
R
L
= 4.7 k
.
Specifications subject to change without notice.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD22151 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
ABSOLUTE MAXIMUM RATING*
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 V
Package Power Dissipation . . . . . . . . . . . . . . . . . . . . . 25 mW
Storage Temperature . . . . . . . . . . . . . . . . . . 50
C to +160
C
Output Sink Current, I
O
. . . . . . . . . . . . . . . . . . . . . . . 15 mA
Magnetic Flux Density . . . . . . . . . . . . . . . . . . . . . . Unlimited
Lead Temperature (Soldering 10 sec) . . . . . . . . . . . . . +300
C
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; the functional operation of
the device at these or any other conditions above those indicated in the operational
sections of this specification is not implied. Exposure to the absolute maximum
rating conditions for extended periods may affect device reliability.
ORDERING GUIDE
Temperature
Package
Package
Model
Range
Description
Option
AD22151YR
40
C to +150
C
8-Lead SOIC
SO-8
WARNING!
ESD SENSITIVE DEVICE
AD22151
3
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PIN CONFIGURATION
TOP VIEW
(Not to Scale)
8
7
6
5
1
2
3
4
AREA OF SENSITIVITY*
TC1
TC2
TC3
GND
V
CC
REF
GAIN
OUTPUT
AD22151
(Not to Scale)
8
7
6
5
1
2
3
4
* SHADED AREA REPRESENTS
MAGNETIC FIELD AREA OF
SENSITIVITY (20MILS 20MILS)
POSITIVE B FIELD INTO TOP OF
PACKAGE RESULTS IN A POSITIVE
VOLTAGE RESPONSE
PIN FUNCTION DESCRIPTIONS
Pin No.
Description
Connection
1
Temperature Compensation 1
Output
2
Temperature Compensation 2
Output
3
Temperature Compensation 3
Input/Output
4
Ground
5
Output
Output
6
Gain
Input
7
Reference
Output
8
Positive Power Supply
CIRCUIT OPERATION
The AD22151 consists of epi Hall plate structures located at
the center of the die. The Hall plates are orthogonally sampled
by commutation switches via a differential amplifier. The two
amplified Hall signals are synchronously demodulated to pro-
vide a resultant offset cancellation (see Figure 3). The demodu-
lated signal passes through a noninverting amplifier to provide
final gain and drive capability. The frequency at which the
output signal is refreshed is 50 kHz.
TEMPERATURE C
0.005
0.004
140
40
120
OFFSET Volts
100
80
60
40
20
0
20
0.004
0
0.001
0.002
0.003
0.003
0.001
0.002
Figure 3. Relative Quiescent Offset vs. Temperature
TEMPERATURE DEPENDENCIES
The uncompensated gain temperature coefficient (G
TCU
) of the
AD22151 is the result of fundamental physical properties asso-
ciated with silicon bulk Hall plate structures. Low doped Hall
plates operated in current bias mode exhibit a temperature
relationship determined by the action of scattering mechanisms
and doping concentration.
The relative value of sensitivity to magnetic field can be altered
by the application of mechanical force upon silicon. The mecha-
nism is principally the redistribution of electrons throughout the
"valleys" of the silicon crystal. Mechanical force on the sensor
is attributable to package-induced stress. The package material
acts to distort the encapsulated silicon altering the Hall cell gain
by
2% and G
TCU
by
200 ppm.
Figure 4 shows the typical G
TCU
characteristic of the AD22151.
This is the observable alteration of gain with respect to tempera-
ture with Pin 3 (TC3) held at a constant 2.5 V (uncompensated).
If a permanent magnet source used in conjunction with the
sensor also displays an intrinsic TC (B
TC
), it will require factor-
ing into the total temperature compensation of the sensor
assembly.
Figures 5 and 6 represent typical overall temperature/gain per-
formance for a sensor and field combination (B
TC
= 200 ppm).
Figure 5 is the total drift in volts over a 40
C to +150
C tem-
perature range with respect to applied field. Figure 6 represents
typical percentage gain variation from +25
C. Figures 7 and 8
show similar data for a B
TC
= 2000 ppm.
TEMPERATURE C
14
4
40
% GAIN
10
60
110
160
12
4
2
0
2
10
6
8
6
Figure 4. Uncompensated Gain Variation (from +25
C) vs.
Temperature
AD22151
4
REV. 0
FIELD Gauss
0.025
DELTA SIGNAL Volts
0.020
0
0.015
0.005
0.010
600
400
200
0
200
400
600
Figure 5. Signal Drift Over Temperature (40
C to +150
C)
vs. Field (200 ppm); +5 V Supply
TEMPERATURE C
0.25
% GAIN
0.20
0
0.15
0.05
0.10
40
10
60
110
160
0.05
Figure 6. Gain Variation from +25
C vs. Temperature
(200 ppm) Field; R1 15 k
FIELD Gauss
0.045
DELTA SIGNAL Volts
0.040
0
0.035
0.025
0.030
800
400
200
0
200
400
600
0.020
0.015
0.010
0.005
600
800
Figure 7. Signal Drift Over Temperature (40
C to +150
C)
vs. Field (2000 ppm); +5 V Supply
TEMPERATURE C
2.0
1.8
1.0
1.6
1.2
1.4
40
10
60
110
160
0.2
0.8
0.6
0.4
0.2
0
% GAIN
Figure 8. Gain Variation (from +25
C) vs. Temperature
(2000 ppm Field; R1 = 12 k
)
TEMPERATURE COMPENSATION
The AD22151 incorporates a "thermistor" transducer that
detects relative chip temperature within the package. This
function provides a compensation mechanism for the various
temperature dependencies of the Hall cell and magnet combina-
tions. The temperature information is accessible at Pins 1 and 2
(
+2900 ppm /
C) and Pin 3 (
2900 ppm/
C) as represented
by Figure 9. The compensation voltages are trimmed to con-
verge at V
CC
/2 at +25
C. Pin 3 is internally connected to the
negative TC voltage via an internal resistor (see Functional
Block Diagram). An external resistor connected between Pin 3
and Pins 1 or 2 will produce a potential division of the two comple-
mentary TC voltages to provide optimal compensation. The
aforementioned Pin 3 internal resistor provides a secondary TC
designed to reduce second order Hall cell temperature sensitivity.
TEMPERATURE C
1.0
VOLTS Reference
0.8
0
0.6
0.2
0.4
150
112
74
2
40
0.2
0.4
0.6
0.8
1.0
36
TC1, TC2 VOLTS
TC3 VOLTS
Figure 9. TC1, TC2 and TC3 with Respect to Reference vs.
Temperature
The voltages present at Pins 1, 2 and 3 are proportional to the
supply voltage. The presence of the Pin 2 internal resistor
distinguishes the effective compensation ranges of Pins 1 and 2
(see temperature configuration in Figures 1 and 2, and typical
resistor values in Figures 10 and 11).
Variation occurs in the operation of the gain temperature
compensation for two reasons. First, the die temperature within
AD22151
5
REV. 0
the package is somewhat higher than the ambient temperature
due to self-heating as a function of power dissipation. Second,
package stress effect alters the specific operating parameters of
the gain compensation, particularly the specific cross over
temperature of TC1, TC3 (
10
C).
CONFIGURATION AND COMPONENT SELECTION
There are three areas of sensor operation that require external
component selection. Temperature compensation (R1), signal
gain (R2
and R3), and offset (R4).
Temperature
If the internal gain compensation is used, an external resistor is
required to complete the gain TC circuit at Pin 3. A number of
factors contribute to the value of this resistor.
a. The intrinsic Hall cell sensitivity TC
950 ppm.
b. Package induced stress variation in a.
150 ppm.
c. Specific field TC
200 ppm (Alnico), 2000 ppm
(Ferrite), 0 ppm (electromagnet) etc.
d. R1, TC.
The final value of target compensation also dictates the use of
either Pin 1 or Pin 2. Pin 1 is provided to allow for large nega-
tive field TC such as ferrite magnets, thus R1 would be con-
nected to Pins 1 and 3.
Pin 2 uses an internal resistive TC to optimize smaller field
coefficients such as Alnico, down to 0 ppm coefficients when
only the sensor gain TC itself is dominant. The TC of R1 itself
will also effect the compensation and as such a low TC resistor
(
50 ppm) is recommended.
Figures 10 and 11 indicate R1 resistor values and their associ-
ated effectiveness for Pins 1 and 2 respectively. Note that the
indicated drift response in both cases incorporates the intrinsic
Hall sensitivity TC (B
TCU
).
For example, the AD22151 sensor is to be used in conjunction
with an Alnico material permanent magnet. The TC of such
magnets is
200 ppm (see Figures 5 and 6). Figure 11 indi-
cates that a compensating drift of +200 ppm at Pin 3 requires a
nominal value of R1 = 18 k
(assuming negligible drift of R1
itself).
R1 k
3500
DRIFT ppm
3000
1000
2500
1500
2000
0
5
10
20
25
500
0
15
30
Figure 10. Typical Resistor Value R1 vs. (Pins 1 and 3)
Drift Compensation
R1 k
800
DRIFT ppm
600
200
400
0
200
0
5
10
20
25
400
600
15
30
35
40
45
50
Figure 11. Typical Resistor Value R1 (Pins 2 and 3) vs.
Drift Compensation
GAIN AND OFFSET
The operation of the AD22151 can be bipolar (i.e., 0 Gauss =
V
CC
/2) or a ratiometric offset can be implemented to Position
Zero Gauss point at some other potential (i.e., 0.25 V).
The gain of the sensor can be set by the appropriate R2 and R3
resistor values (see Figure 1) such that:
Gain
=
1
+
R3
R2
0.4 mV /G
(1)
However, if an offset is required to position the quiescent out-
put at some other voltage then the gain relationship is modified
to:
Gain
=
1
+
R3
(R2 R4)
0.4 mV /G
(2)
The offset that R4
introduces is:
Offset
=
R3
(R3
+
R4)
V
CC
V
OUT
(
)
(3)
For example:
At V
CC
= 5 V at room temperature, the internal gain of the
sensor is approximately 0.4 mV/Gauss. If a sensitivity of 6 mV/
Gauss is required with a quiescent output voltage of 1 V, the
following calculations apply (see Figure 2 ).
A value for R3 would be selected that complied with the various
considerations of current and power dissipation, trim ranges (if
applicable), etc. For the purpose of example assume a value of
85 k
.
To achieve a quiescent offset of 1 V requires a value for R4 as:
V
CC
2
1
V
CC
1
=
0.375
(4)
Thus:
R4
=
85 k
0.375
85 k
=
141.666 k
(5)
The gain required would be 6/0.4 (mV/Gauss) = 15
AD22151
6
REV. 0
Knowing the values of R3 and R4
from above, and noting Equa-
tion 2, the parallel combination of R2 and R4 required is:
85 k
15 1
( )
=
6.071 k
Thus:
R2
=
1
1
6.071 k
1
141.666 k
=
6.342 k
NOISE
The principle noise component in the sensor is thermal noise
from the Hall cell. Clock feedthrough into the output signal is
largely suppressed with application of a supply bypass capacitor.
Figure 12 shows the power spectral density (PSD) of the output
signal for a gain of 5 mV/Gauss. The effective bandwidth of the
sensor is approximately 5.7 kHz. This is shown by Figure 13
small signal bandwidth vs. gain. The PSD indicates an rms
noise voltage of 2.8 mV within the 3 dB bandwidth of the sen-
sor. A wideband measurement of 250 MHz indicates 3.2 mV
rms (see Figure 14a).
In many position sensing applications bandwidth requirements
can be as low as 100 Hz. Passing the output signal through an
LP filter, for example 100 Hz, would reduce the rms noise volt-
age to
1 mV. A dominant pole may be introduced into the
output amplifier response by connection of a capacitor across
feedback resistor R3, as a simple means of reducing noise at the
expense of bandwidth. Figure 14b indicates the output signal of
a 5 mV/G sensor bandwidth limited to 180 Hz with a 0.01
F
feedback capacitor.
Note: Measurements taken with 0.1
F decoupling capacitor
between V
CC
and GND at +25
C.
LOGMAG
5 dB
/div
100
H
1
H
START: 64 Hz
NOISE: PSD (8 mV/GAUSS)
STOP: 25.6 kHz
RMS: 64
B MARKER X 64Hz
Y: 3.351 H
Figure 12. Power Spectral Density (5 mV/G)
3dB FREQ. (kHz)
GAIN mV/GAUSS
7
FREQUENCY kHz
6
2
5
3
4
1
2
3
1
0
4
5
6
Figure 13. Small-Signal Gain Bandwidth
CH2
10.0mV
BW
M2.00ms
2
TEK
STOP:
25.0 kS/s
[
[
T
3ACQS
T
CH2 PK-PK
19.2mV
Figure 14a. Peak-to-Peak Full Bandwidth (10 mV/Division)
CH2
10.0mV
BW
M2.00ms
2
TEK
STOP:
25.0 kS/s
[
[
T
7ACQS
T
CH2 PK-PK
4.4mV
Figure 14b. Peak-to-Peak 180 Hz Bandwidth
(10 mV/Division)
AD22151
7
REV. 0
TEMPERATURE C
2.496
VOLTS
2.494
2.492
2.488
2.490
140
120
100
80
60
40
20
2.486
2.484
0
40
20
GAIN = 3.78mV/G
Figure 16. Absolute Offset Volts vs. Temperature
FIELD Gauss
0.06
0.05
0.04
0.02
0.03
600
400
200
0
200
400
600
0.01
0
0.01
0.02
0.03
0.04
0.05
% ERROR
Figure 15. Integral Nonlinearity vs. Field
AD22151
8
REV. 0
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
C3213810/97
PRINTED IN U.S.A.
8-Lead SOIC
(SO-8)
0.1968 (5.00)
0.1890 (4.80)
8
5
4
1
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.0688 (1.75)
0.0532 (1.35)
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.0500
(1.27)
BSC
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8
0
0.0196 (0.50)
0.0099 (0.25)
x 45
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