AD22151YR(Rev0) 查看數據表（PDF） - Analog Devices
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AD22151YR Datasheet PDF : 8 Pages
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AD22151
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 (BTCU).
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 kΩ (assuming negligible drift of R1
itself).
3500
3000
2500
2000
1500
1000
500
0
0
5
10
15
20
25
30
R1 – k⍀
Figure 10. Typical Resistor Value R1 vs. (Pins 1 and 3)
Drift Compensation
800
600
400
200
0
–200
–400
–600
0
5 10 15 20 25 30 35 40 45 50
R1 – k⍀
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 =
VCC/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 × 0.4 mV /G
(1)
R2
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
(R2ʈR4)
×
0.4
mV
/G
(2)
The offset that R4 introduces is:
( ) Offset
= R3 ×
(R3 + R4)
V CC
– V OUT
(3)
For example:
At VCC = 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 kΩ.
To achieve a quiescent offset of 1 V requires a value for R4 as:
V CC
2
–
1
=
0.375
(4)
V CC –1
Thus:
R4
=
85 kΩ
0.375
–
85
kΩ
=
141.666
kΩ
(5)
The gain required would be 6/0.4 (mV/Gauss) = 15
REV. 0
–5–
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