參數(shù)資料
型號: ADXL250
廠商: Analog Devices, Inc.
英文描述: Low Power,65 g to 650 g, Low Noise,Single/Dual Axis Accelerometers(低功耗、測量范圍為65g到650g的低噪音單/雙軸雙軸加速器)
中文描述: 低功耗,65克至650克,低噪聲,單/雙軸加速度(低功耗,測量范圍為65克到650克的低噪音單/雙軸雙軸加速器)
文件頁數(shù): 11/15頁
文件大小: 291K
代理商: ADXL250
ADXL150/ADXL250
–11–
REV. 0
2-POLE
FILTER
R2
42.2k
V
R3
82.5k
V
R1
82.5k
V
+V
S
200k
V
0gTRIM
R6
1M
V
R5
R4
100k
V
OUTPUT
SCALING
AMPLIFIER
BW
C3
C4
TYPICAL FILTER VALUES
300Hz
100Hz
30Hz
10Hz
0.027
m
F 0.0033
m
F
0.082
m
F 0.01
m
F
0.27
m
F
0.82
m
F
0.033
m
F
0.1
m
F
+V
S
0.1
m
F
C2
0.1
m
F
+V
S
2
SELF-TEST
+V
S
2
25k
V
5k
V
ADXL150
GAIN
AMP
OFFSET
NULL
COM
C1
0.1
m
F
BUFFER
AMP
DEMODULATOR
SENSOR
+V
S
TP
(DO NOT CONNECT)
5
14
9
10
7
CLOCK
1/2
OP296
3
1
2
8
EXT
AMP
GAIN
R5
VALUE
F.S.
RANGE
DESIRED
OUTPUT
SCALE FACTOR
76mV/g
100mV/g
200mV/g
400mV/g
±25g
±20g
±10g
±5g
2.0
2.6
5.3
10.5
200k
V
261k
V
536k
V
1M
V
C3
C4
+V
S
2
1/2
OP296
5
4
7
6
Figure 21. Two-Pole Post Filter Circuit
for various full-scale
g
levels and approximate circuit band-
widths. For bandwidths other than those listed, use the
formula:
Cf
=
1
2
π
R
3
(
)
Desired
3
dB Bandwidth in Hz
or simply scale the value of capacitor Cf accordingly; i.e., for an
application with a 50 Hz bandwidth, the value of Cf will need
to be twice as large as its 100 Hz value. If further noise reduc-
tion is needed while maintaining the maximum possible band-
width, a 2- or 3-pole post filter is recommended. These provide
a much steeper roll-off of noise above the pole frequency. Fig-
ure 21 shows a circuit that provides 2-pole post filtering. Com-
ponent values for the 2-pole filter were selected to operate the
first op amp at unity gain. Capacitors C3 and C4 were chosen
to provide 3 dB bandwidths of 10 Hz, 30 Hz, 100 Hz and
300 Hz.
The second op amp offsets and scales the output to provide a
+2.5 V
±
2 V output over a wide range of full-scale
g
levels.
APPLICATION HINTS
ADXL250 Power Supply Pins
When wiring the ADXL250, be sure to connect BOTH power
supply terminals, Pins 14 and 13.
Ratiometric Operation
Ratiometric operation means that the circuit uses the power
supply as its voltage reference. If the supply voltage varies, the
accelerometer and the other circuit components (such as an
ADC, etc.) track each other and compensate for the change.
Figure 22 shows how both the zero
g
offset and output sensitiv-
ity of the ADXL150/ADXL250 vary with changes in supply
voltage. If they are to be used with nonratiometric devices, such
as an ADC with a built-in 5 V reference, then both components
should be referenced to the same source, in this case the ADC
reference. Alternatively, the circuit can be powered from an
external +5 volt reference.
POWER SUPPLY VOLTAGE
2.65
2.50
2.35
5.25 5.20 5.15 5.10 5.05 5.00 4.95 4.90
4.85 4.80 4.75
2.60
2.55
2.45
2.40
40.25
38.00
35.75
S
39.50
38.75
37.25
36.50
0
Figure 22. Typical Ratiometric Operation
Since any voltage variation is transferred to the accelerometer’s
output, it is important to reduce any power supply noise. Simply
following good engineering practice of bypassing the power supply
right at Pin 14 of the ADXL150/ADXL250 with a 0.1
μ
F ca-
pacitor should be sufficient.
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