ADXL50 データシートの表示（PDF） - Analog Devices
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ADXL50 Datasheet PDF : 16 Pages
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ADXL50
Compensating for the 0 g Drift of the ADXL50 Accelerometer
The circuit of Figure 29 provides a linear temperature compen-
sation for the ADXL50. Figure 30 shows the 0 g drift over tem-
perature for a typical ADXL50 with and without this circuit. As
shown by Figure 30, the linear portion of the drift curve has
been subtracted out. In effect, the curve has been rotated coun-
terclockwise until it is horizontal, leaving just the bow of the
curve: that portion which is not linear. As shown by Figure 30,
over a +25°C to +70°C range, a 10× reduction in drift is achieved.
The circuit of Figure 29 is essentially a temperature sensor
coupled to a Whetstone bridge. The AD590 provides a 1 µA/°K
current output whose voltage scale factor is set by resistor RA.
The bridge circuit subtracts out the nominal 298 mV output of
the AD590 at +25°C and leaves only the change in temperature,
which is what is needed. Without the bridge, the 298 mV room
temperature “offset” would “swamp” the much smaller change
in output with temperature.
Resistors R5 and R6 form a resistor divider (one half of the
bridge) which divides down the +3.4 V reference output of the
ADXL50 to 0.3 V which appears at the noninverting input of
the AD820 op amp. Resistors R7 and R8 form the other half of
the bridge, and because they have the same ratio as R5 and R6,
the op amp will have a +3.4 V output at room temperature.
0.022µF
4
C2
ADXL50
1.8V
0.022µF
C1
2
3
C1
PRE-AMP
5
COM
6
+3.4V
REF
8
10
VPR
49.9kΩ VIN–
BUFFER
AMP
499kΩ
1
+5V
0.1µF
C3
9
VOUT
R1
R3 TEMPERATURE
+5V
COMPENSATED
ACCELERATION
OUTPUT
1µA/°K
AD590
3101kΩ
R5
TC
COMP
10kΩ SET
500Ω R4
RB
BRIDGE
30k
BALANCE
R6
1kΩ RA
310kΩ
R7
+5V
TEST
0.01µF
POINT
"A"
3
7
R9
2 AD820 6
4 TEMPCO
20kΩ
30k
AMPLIFIER
R8
49.9kΩ
R2
0g OUTPUT
LEVEL
R10
RC 25kΩ
20kΩ
+15
+10
+5
0
–5
–10
–15
–20
–25
–30
–35
–40
–45
–55
LOW TEMP TRIM
HIGH TEMP TRIM
COMPENSATED XL50
UNCOMPENSATED XL50
–35 –15 +5 +25 +45 +65 +85 +105
TEMPERATURE – °C
Figure 30. ADXL50 0 g Drift With and Without the Com-
pensation Circuit of Figure 29
ADXL50 Application Literature Available
Contact the Analog Devices Literature Center for a copy of
publication number G2112, the Accelerometer Application
Guide. This includes all current application notes and data
sheets for Analog Devices’ accelerometers.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
0.185 (4.70)
0.165 (4.19)
REFERENCE PLANE
0.750 (19.05)
0.500 (12.70)
0.160 (4.06)
0.110 (2.79)
0.335 (8.51)
0.305 (7.75)
0.370 (9.40)
0.335 (8.51)
0.040 (1.02) MAX
0.045 (1.14)
0.010 (0.25)
0.115
(2.92)
BSC
6
5
4
3
2
1
7
8
9
10
0.045 (1.14)
0.027 (0.69)
0.230 (5.84)
BSC
0.034 (0.86)
0.027 (0.69)
SEATING PLANE
CALIBRATION PROCEEDURE:
AT TMIN OR LOWER TEMP CAL POINT...
1. SET RB ALL THE WAY TO ONE SIDE.
2. ADJUST RA FOR +3.4V AT TEST POINT "A."
3. SET RC FOR +2.5V VOUT (AT PIN 9 OF ADXL50).
4. TEMPORARILY CONNECT A 1.5kΩ RESISTOR BETWEEN
THE CENTER OF RB AND GROUND.
5. ADJUST RB FOR +2.5V AT VOUT.
6. REMOVE THE 1.5kΩ RESISTOR. VOUT SHOULD NOT CHANGE.
7. GO TO TMAX OR HIGH TEMP CAL POINT.
8. READJUST RB FOR +2.5V.
9. CALIBRATION COMPLETE.
Figure 29. ADXL50 0 g Drift Compensation Circuit
–16–
REV. B
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