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ADXL325 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADXL325
Beschreibung Accelerometer
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 17 Seiten
ADXL325 Datasheet, Funktion
FEATURES
3-axis sensing
Small, low profile package
4 mm × 4 mm × 1.45 mm LFCSP
Low power: 350 μA typical
Single-supply operation: 1.8 V to 3.6 V
10,000 g shock survival
Excellent temperature stability
Bandwidth adjustment with a single capacitor per axis
RoHS/WEEE lead-free compliant
APPLICATIONS
Cost-sensitive, low power, motion- and tilt-sensing applications
Mobile devices
Gaming systems
Disk drive protection
Image stabilization
Sports and health devices
Small, Low Power, 3-Axis ±5 g
Accelerometer
ADXL325
GENERAL DESCRIPTION
The ADXL325 is a small, low power, complete 3-axis accelerometer
with signal conditioned voltage outputs. The product measures
acceleration with a minimum full-scale range of ±5 g. It can
measure the static acceleration of gravity in tilt-sensing applications,
as well as dynamic acceleration, resulting from motion, shock,
or vibration.
The user selects the bandwidth of the accelerometer using
the CX, CY, and CZ capacitors at the XOUT, YOUT, and ZOUT pins.
Bandwidths can be selected to suit the application with a range
of 0.5 Hz to 1600 Hz for X and Y axes and a range of 0.5 Hz to
550 Hz for the Z axis.
The ADXL325 is available in a small, low profile, 4 mm ×
4 mm × 1.45 mm, 16-lead, plastic lead frame chip scale package
(LFCSP_LQ).
FUNCTIONAL BLOCK DIAGRAM
+3V
VS
ADXL325
~32kXOUT
OUTPUT AMP
CDC
3-AXIS
SENSOR
AC AMP
DEMOD
~32k
OUTPUT AMP
CX
YOUT
CY
~32k
OUTPUT AMP
ZOUT
CZ
COM
ST
Figure 1.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.






ADXL325 Datasheet, Funktion
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Table 3. Pin Function Descriptions
Pin No.
Mnemonic
1 NC
2 ST
3 COM
4 NC
5 COM
6 COM
7 COM
8 ZOUT
9 NC
10 YOUT
11 NC
12 XOUT
13 NC
14 VS
15 VS
16 NC
EP Exposed pad
NC
ST
COM
NC
16 15 14 13
1 ADXL325 12
TOP VIEW
2 (Not to Scale) 11
+Y
3 +Z
10
4
5
+X
67
9
8
XOUT
NC
YOUT
NC
NC = NO CONNECT
Figure 2. Pin Configuration
Description
No Connect (or Optionally Ground)
Self Test
Common
No Connect
Common
Common
Common
Z Channel Output
No Connect (or Optionally Ground)
Y Channel Output
No Connect
X Channel Output
No Connect
Supply Voltage (1.8 V to 3.6 V)
Supply Voltage (1.8 V to 3.6 V)
No Connect
Not internally connected. Solder for mechanical integrity.
ADXL325
Rev. 0 | Page 5 of 16

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ADXL325 pdf, datenblatt
ADXL325
APPLICATIONS INFORMATION
POWER SUPPLY DECOUPLING
For most applications, a single 0.1 μF capacitor, CDC, placed
close to the ADXL325 supply pins adequately decouples the
accelerometer from noise on the power supply. However, in
applications where noise is present at the 50 kHz internal clock
frequency (or any harmonic thereof), additional care in power
supply bypassing is required because this noise can cause errors
in acceleration measurement. If additional decoupling is needed, a
100 Ω (or smaller) resistor or ferrite bead can be inserted in the
supply line. Additionally, a larger bulk bypass capacitor (1 μF or
greater) can be added in parallel to CDC. Ensure that the connection
from the ADXL325 ground to the power supply ground is low
impedance because noise transmitted through ground has a
similar effect as noise transmitted through VS.
SETTING THE BANDWIDTH USING CX, CY, AND CZ
The ADXL325 has provisions for band limiting the XOUT,
YOUT, and ZOUT pins. Capacitors must be added at these pins to
implement low-pass filtering for antialiasing and noise reduction.
The 3 dB bandwidth equation is
DESIGN TRADE-OFFS FOR SELECTING FILTER
CHARACTERISTICS: THE NOISE/BW TRADE-OFF
The selected accelerometer bandwidth ultimately determines
the measurement resolution (smallest detectable acceleration).
Filtering can be used to lower the noise floor to improve the
resolution of the accelerometer. Resolution is dependent on the
analog filter bandwidth at XOUT, YOUT, and ZOUT.
The output of the ADXL325 has a typical bandwidth greater
than 500 Hz. 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 ADXL325 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 bandwidth). The user should limit bandwidth
to the lowest frequency needed by the application to maximize
the resolution and dynamic range of the accelerometer.
f−3 dB = 1/(2π(32 kΩ) × C(X, Y, Z))
or more simply
f–3 dB = 5 μF/C(X, Y, Z)
The tolerance of the internal resistor (RFILT) typically varies as
much as ±15% of its nominal value (32 kΩ), and the bandwidth
varies accordingly. A minimum capacitance of 0.0047 μF for CX,
CY, and CZ is recommended in all cases.
Table 4. Filter Capacitor Selection, CX, CY, and CZ
Bandwidth (Hz)
Capacitor (μF)
1 4.7
10 0.47
50 0.10
100 0.05
200 0.027
500 0.01
SELF TEST
The ST pin controls the self test feature. When this pin is set to
VS, an electrostatic force is exerted on the accelerometer beam.
The resulting movement of the beam allows the user to test
whether the accelerometer is functional. The typical change in
output is −1.08 g (corresponding to −190 mV) in the X axis,
+1.08 g (+190 mV) on the Y axis, and +1.83 g (+320 mV) on the
Z axis. This ST pin can be left open circuit or connected to
common (COM) in normal use.
Never expose the ST pin to voltages greater than VS + 0.3 V. If
this cannot be guaranteed due to the system design (for instance,
there are multiple supply voltages), then a low VF clamping
diode between ST and VS is recommended.
With the single-pole roll-off characteristic, the typical noise of
the ADXL325 is determined by
rms Noise = Noise Density × ( BW ×1.6 )
Often, the peak value of the noise is desired. Peak-to-peak noise
can only be estimated by statistical methods. Table 5 is useful for
estimating the probabilities of exceeding various peak values, given
the rms value.
Table 5. Estimation of Peak-to-Peak Noise
Peak-to-Peak Value
% of Time That Noise Exceeds
Nominal Peak-to-Peak Value
2 × rms
32
4 × rms
4.6
6 × rms
0.27
8 × rms
0.006
USE WITH OPERATING VOLTAGES OTHER THAN 3 V
The ADXL325 is tested and specified at VS = 3 V; however, it can be
powered with VS as low as 1.8 V or as high as 3.6 V. Note that some
performance parameters change as the supply voltage is varied.
The ADXL325 output is ratiometric; therefore, the output
sensitivity (or scale factor) varies proportionally to the supply
voltage. At VS = 3.6 V, the output sensitivity is typically 209 mV/g.
At VS = 2 V, the output sensitivity is typically 116 mV/g.
The zero g bias output is also ratiometric; therefore, the zero g
output is nominally equal to VS/2 at all supply voltages.
The output noise is not ratiometric but is absolute in volts; therefore,
the noise density decreases as the supply voltage increases. This
is because the scale factor (mV/g) increases while the noise voltage
remains constant. At VS = 3.6 V, the X- and Y-axis noise density
is typically 200 μg/√Hz, while at VS = 2 V, the X- and Y-axis
noise density is typically 300 μg/√Hz.
Rev. 0 | Page 11 of 16

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