ADXL320JCP Analog Devices Inc, ADXL320JCP Datasheet - Page 12

• Manufacturer Part Number: ADXL320JCP
• Description: IC, 2 AXIS ACCELEROMETER, ± 5G, LFCSP-16
• Manufacturer: Analog Devices Inc
• Series: iMEMS®r

Specifications of ADXL320JCP

• No. Of Axes: 2
• Sensor Case Style: LFCSP
• No. Of Pins: 16
• Supply Voltage Range: 2.4V To 5.25V
• Operating Temperature Range: -20°C To +70°C
• Msl: MSL 1 - Unlimited
• Acceleration Range: ± 5g
• Axis: X, Y
• Sensitivity: 174mV/g
• Voltage - Supply: 2.4 V ~ 5.25 V
• Output Type: Analog
• Bandwidth: 1Hz ~ 500Hz Selectable
• Mounting Type: Surface Mount
• Package / Case: 16-LQFN, CSP Exposed Pad
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: ADXL320EB - BOARD EVAL FOR ADXL320
• Interface: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: Q2045089

ADXL320
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 may cause interference on the
ADXL320 output. If additional decoupling is needed, a 100 Ω
(or smaller) resistor or ferrite bead may be inserted in the
supply line. Additionally, a larger bulk bypass capacitor (in the
1 μF to 4.7 μF range) may be added in parallel to C
SETTING THE BANDWIDTH USING C
The ADXL320 has provisions for band-limiting the X
Y
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 ±15% of its nominal value (32 kΩ), and the bandwidth
varies accordingly. A minimum capacitance of 2000 pF for C
and C
Table 5. 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
The resulting movement of the beam allows the user to test if
the accelerometer is functional. The typical change in output is
315 mg (corresponding to 55 mV). This pin may be left open-
circuit or connected to common (COM) in normal use.
The ST pin should never be exposed to voltages greater than
V
design (for instance, if there are multiple supply voltages), then
a low V
OUT
S
S
, an electrostatic force is exerted on the accelerometer beam.
+ 0.3 V. If this cannot be guaranteed due to the system
F
F
pins. Capacitors must be added at these pins to implement
−3 dB
–3 dB
Y
is required in all cases.
F
clamping diode between ST and V
= 5 μF/C
= 1/(2π(32 kΩ) × C
(X, Y)
(X, Y)
)
Capacitor (μF)
4.7
0.47
0.10
0.05
0.027
0.01
X
FILT
and C
) typically varies as
S
is recommended.
X
Y
AND C
DC
DC
, adequately
.
OUT
Y
and
Rev. 0 | Page 12 of 16
X
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, which improves
the resolution of the accelerometer. Resolution is dependent on
the analog filter bandwidth at X
The output of the ADXL320 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
A/D sampling frequency to minimize aliasing. The analog
bandwidth may be further decreased to reduce noise and
improve resolution.
The ADXL320 noise has the characteristics of white Gaussian
noise, which contributes equally at all frequencies and is
described in terms of μg/√Hz (the noise is proportional to the
square root of the accelerometer’s bandwidth). The user should
limit bandwidth to the lowest frequency needed by the
application in order to maximize the resolution and dynamic
range of the accelerometer.
With the single-pole, roll-off characteristic, the typical noise of
the ADXL320 is determined by
At 100 Hz bandwidth the noise will be
Often, the peak value of the noise is desired. Peak-to-peak noise
can only be estimated by statistical methods. Table 6 is useful
for estimating the probabilities of exceeding various peak
values, given the rms value.
Table 6. Estimation of Peak-to-Peak Noise
Peak-to-Peak Value
2 × rms
4 × rms
6 × rms
8 × rms
rmsNoise
rmsNoise
=
=
(250
(250
μg/
μg/
% of Time That Noise Exceeds
Nominal Peak-to-Peak Value
32
4.6
0.27
0.006
Hz
Hz
)
)
×
×
OUT
(
(
100
and Y
BW
×
×
1.6
1.6
OUT
)
.
)
=
3.2
mg