ADXL203EB Analog Devices Inc, ADXL203EB Datasheet - Page 10

• Manufacturer Part Number: ADXL203EB
• Description: ±1.7g Dual-Axis IMEMS Accelerometer Evaluation Board
• Manufacturer: Analog Devices Inc
• Series: iMEMS®r

Specifications of ADXL203EB

• Silicon Manufacturer: Analog Devices
• Application Sub Type: Accelerometer - Dual-Axis
• Kit Application Type: Sensing - Motion / Vibration / Shock
• Silicon Core Number: ADXL203
• Sensor Type: Accelerometer, 2 Axis
• Sensing Range: ±1.7g
• Interface: Analog
• Sensitivity: 1000mV/g
• Voltage - Supply: 3 V ~ 6 V
• Embedded: No
• Utilized Ic / Part: ADXL203
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: Q1875695

ADXL103/ADXL203
APPLICATIONS
POWER SUPPLY DECOUPLING
For most applications, a single 0.1 μF capacitor, C
decouples the accelerometer from noise on the power supply.
However in some cases, particularly where noise is present at
the 140 kHz internal clock frequency (or any harmonic thereof),
noise on the supply can cause interference on the ADXL103/
ADXL203 output. If additional decoupling is needed, a 100 Ω
(or smaller) resistor or ferrite beads can be inserted in the supply
line of the ADXL103/ADXL203. Additionally, a larger bulk
bypass capacitor (in the 1 μF to 22 μF range) can be added in
parallel to C
SETTING THE BANDWIDTH USING C
The ADXL103/ADXL203 has provisions for band limiting the
X
implement low-pass filtering for antialiasing and noise reduction.
The equation for the 3 dB bandwidth is
or more simply,
The tolerance of the internal resistor (R
much as ±25% of its nominal value (32 kΩ); thus, the bandwidth
varies accordingly. A minimum capacitance of 2000 pF for C
C
Table 6. Filter Capacitor Selection, C
Bandwidth (Hz)
1
10
50
100
200
500
SELF TEST
The ST pin controls the self-test feature. When this pin is set to
V
ometer. The resulting movement of the beam allows the user to
test if the accelerometer is functional. The typical change in
output is 750 mg (corresponding to 750 mV). This pin can be
left open-circuit or connected to common in normal use.
The ST pin should never be exposed to voltage greater than
V
cannot be guaranteed (that is, multiple supply voltages are
present), a low V
recommended.
OUT
Y
S
S
, an electrostatic force is exerted on the beam of the acceler-
is required in all cases.
+ 0.3 V. If the system design is such that this condition
F
F
and Y
–3 dB
–3 dB
= 1/(2π(32 kΩ) × C
= 5 μF/C
OUT
DC
.
pins. Capacitors must be added at these pins to
F
clamping diode between ST and V
(X, Y)
(X, Y)
)
Capacitor (μF)
4.7
0.47
0.10
0.05
0.027
0.01
X
FILT
and C
) can vary typically as
X
Y
AND C
DC
, adequately
S
is
Y
X
Rev. C | Page 10 of 12
and
DESIGN TRADE-OFFS FOR SELECTING FILTER
CHARACTERISTICS: THE NOISE/BW TRADE-OFF
The accelerometer bandwidth selected ultimately determines
the measurement resolution (smallest detectable acceleration).
Filtering can be used to lower the noise floor, improving the
resolution of the accelerometer. Resolution is dependent on the
analog filter bandwidth at X
The output of the ADXL103/ADXL203 has a typical bandwidth
of 2.5 kHz. The user must filter the signal at this point to limit
aliasing errors. The analog bandwidth must be no more than
half the analog-to-digital sampling frequency to minimize
aliasing. The analog bandwidth can be further decreased to
reduce noise and improve resolution.
The ADXL103/ADXL203 noise has the characteristics of white
Gaussian noise, which contributes equally at all frequencies and
is described in terms of μg/√Hz (that is, the noise is proportional to
the square root of the accelerometer bandwidth). The user should
limit bandwidth to the lowest frequency needed by the application
to maximize the resolution and dynamic range of the
accelerometer.
With the single pole roll-off characteristic, the typical noise of
the ADXL103/ADXL203 is determined by
At 100 Hz, the noise is
Often, the peak value of the noise is desired. Peak-to-peak noise
can only be estimated by statistical methods. Table 7 is useful
for estimating the probabilities of exceeding various peak
values, given the rms value.
Table 7. Estimation of Peak-to-Peak Noise
Peak-to-Peak Value
2 × rms
4 × rms
6 × rms
8 × rms
rmsNoise
rmsNoise


(
(
110
110
μ
μ
g
g
/
% of Time That Noise Exceeds
Nominal Peak-to-Peak Value
32
4.6
0.27
0.006
/
OUT
Hz
Hz
and Y
)
)


(
(
100
BW
OUT
.


. 1
. 1
) 6
) 6

1
4 .
m
g