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APPLICATIONS:
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CREATED DATE – 11/29/2014
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MODIFIED BY – MARIA TIMBERLAND
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DESCRIPTION – accelerometer details and it use.
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AUTHOR NAME - CHARLES J JASON
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LICENSE - FREE
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CREATED FOR - S4silver.blogspot.in users
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ADXL335
- ACCELEROMETER
ADXL is
a small, thin low power ,complete 3-axis accelerometer with conditioned voltage
outputs. The product measures acceleration with a minimam full scale range of
+/- 3g.It can measure 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,cyand cz capacitors at
the Xout, Yout and Zout pins. Bandwidth can be selected to suit the application
,with a range of 0.5Hz to 1600 Hz for the X and Y axis,and a range of 0.5 Hzto
550 Hz for the Z axis.
The
ADXL335 is available in a small ,low profile 4mm x 4mm x 1.45mm,16 lead,plastic
lead framechip mscale package.
FEATURES:
1.
3-axis sensing
2.
Small low profile package
3.
Low power:350uA(typical)
4.
Single-supply operation:1.8V to 3.6 V
5.
10,000 g shock survival
6.
Excellent temperature stability
7.
BW adjustment with a single capacitor
per axis
8.
RoHS/WEEE lead free complaint
1.
Cost sensitive, low power ,motion and
tilt-sensing applications
2.
Mobile devices
3.
Gaming systems
4.
Disc drive protection
5.
Image stabilization
6.
Sports and health devices
ABSOLUTE
MAXIMUM RATINGS:
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PARAMETER
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RATINGS
|
|
Acceleration(any
axis,unpowered)
Acceleration(any
axis,powered)
Vs
All other pins
Output short circuit
duration (Any pin to common)
Temperature range(Powered)
Temperature range(Storage)
|
10,000g
10,000g
-0.3V to +3.6V
(Com-0.3V) to(Vs+3.6V)
Indefinite
-55c to +125c
-65c to 150c
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THEORY OF OPERATION
The ADXL335 is a complete 3-axis acceleration
measurement system. The ADXL335 has a measurement range of ±3 g mini-mum.
It contains a polysilicon surface-micro-machined sensor and signal conditioning
circuitry to implement an open-loop acceleration measurement architecture. The
output signals are analog voltages that are proportional to acceleration. The
accelerometer 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 the X and Y axes, and a range of 0.5 Hz to 550 Hz for the Z axis.
The sensor is a polysilicon surface-micromachined
structure built on top of a silicon wafer. Polysilicon springs suspend the
structure over the surface of the wafer and provide a resistance against
acceleration forces. Deflection of the structure is measured using a
differential capacitor that consists of independent fixed plates and plates
attached to the moving mass. The fixed plates are driven by 180° out-of-phase
square waves. Acceleration deflects the moving mass and unbalances the
differential capacitor resulting in a sensor output whose amplitude is
proportional to acceleration. Phase-sensitive demodulation techniques are then
used to determine the magnitude and direction of the acceleration.
The
demodulator output is amplified and brought off-chip through a 32 kΩ resistor.
The user then sets the signal bandwidth of the device by adding a capacitor.
This filtering improves measurement resolution and helps prevent aliasing.
MECHANICAL
SENSOR
The
ADXL335 uses a single structure for sensing the X, Y, and Z axes. As a result,
the three axes’ sense directions are highly orthogonal and have little
cross-axis sensitivity. Mechanical misalignment of the sensor die to the
package is the chief source of cross-axis sensitivity. Mechanical misalignment
can, of course, be calibrated out at the system level.
PERFORMANCE
Rather
than using additional temperature compensation circui-try, innovative design
techniques ensure that high performance is built in to the ADXL335. As a
result, there is no quantization error or nonmonotonic behavior, and
temperature hysteresis is very low (typically less than 3 mg over the −25°C to
+70°C temperature range).
POWER
SUPPLY DECOUPLING
For most
applications, a single 0.1 μF capacitor, CDC, placed close to the ADXL335
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 ADXL335 ground
to the power supply ground is low impedance because noise transmitted through
ground has a similar effect to noise transmitted through VS.
SETTING
THE BANDWIDTH USING CX, CY, AND CZ
The
ADXL335 has provisions for band limiting the XOUT, YOUT, and ZOUT pins.
Capacitors must be added at these pins to imple-ment low-pass filtering for
antialiasing and noise reduction. The equation for the 3 dB bandwidth is
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.
FUNCTIONAL BLOCK DIAGRAM
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