
ADXL50
–16–
REV. B
P
C
+15
–45
+105
–30
–40
–35
–35
–55
–15
–25
–20
–10
–5
0
+10
+5
+85
+65
+45
+25
+5
–15
HIGH TEMP TRIM
LOW TEMP TRIM
COMPENSATED XL50
UNCOMPENSATED XL50
TEMPERATURE –
°
C
M
Figure 30. ADXL50 0 g Drift With and Without the Com-
pensation Circuit of Figure 29
ADX L50 Application Literature Available
Contact the Analog Devices Literature Center for a copy of
publication number G2112, the Accelerometer Application
Guide. T his includes all current application notes and data
sheets for Analog Devices’ accelerometers.
OUT LINE DIME NSIONS
Dimensions shown in inches and (mm).
0.160 (4.06)
0.110 (2.79)
0.034 (0.86)
0.027 (0.69)
0.045 (1.14)
0.027 (0.69)
0.115
(2.92)
BSC
6
8
5
7
1
4
2
3
9
10
0.230 (5.84)
BSC
REFERENCE PLANE
SEATING PLANE
0.335 (8.51)
0.305 (7.75)
0.370 (9.40)
0.335 (8.51)
0.750 (19.05)
0.500 (12.70)
0.045 (1.14)
0.010 (0.25)
0.040 (1.02) MAX
0.185 (4.70)
0.165 (4.19)
Compensating for the 0 g Drift of the ADX L50 Accelerometer
T he circuit of Figure 29 provides a linear temperature compen-
sation for the ADX L50. Figure 30 shows the 0 g drift over tem-
perature for a typical ADX L50 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.
T he circuit of Figure 29 is essentially a temperature sensor
coupled to a Whetstone bridge. T he AD590 provides a 1
μ
A/
°
K
current output whose voltage scale factor is set by resistor RA.
T he 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
ADX L50 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.
BUFFER
AMP
ADXL50
PRE-AMP
0.022
μ
F
C1
C1
0.022
μ
F
C2
COM
0.1
μ
F
C3
+5V
V
OUT
V
IN–
V
PR
+3.4V
REF
R1
R3
1.8V
310k
R7
+5V
7
2
3
6
4
0.01
μ
F
AD820
10
8
5
3
2
4
9
1
6
499k
TEMPERATURE
COMPENSATED
ACCELERATION
OUTPUT
49.9k
3101k
R5
RB
TC
COMP
SET
10k
R4
500
BRIDGE
BALANCE
RA
1k
AD590
+5V
1
μ
A/
°
K
TEMPCO
AMPLIFIER
R9
20k
RC
20k
49.9k
R2
R10
25k
0g OUTPUT
LEVEL
CALIBRATION PROCEEDURE:
AT T
MIN
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 V
(AT PIN 9 OF ADXL50).
4. TEMPORARILY CONNECT A 1.5k
RESISTOR BETWEEN
THE CENTER OF RB AND GROUND.
5. ADJUST RB FOR +2.5V AT V
.
6. REMOVE THE 1.5k
RESISTOR. V
SHOULD NOT CHANGE.
7. GO TO T
OR HIGH TEMP CAL POINT.
8. READJUST RB FOR +2.5V.
9. CALIBRATION COMPLETE.
Figure 29. ADXL50 0 g Drift Compensation Circuit
TEST
POINT
"A"
30k
R8
30k
R6