EVAL-ADXL343Z-M Analog Devices, EVAL-ADXL343Z-M Datasheet - Page 29

• Manufacturer Part Number: EVAL-ADXL343Z-M
• Description: Acceleration Sensor Development Tools EB
• Manufacturer: Analog Devices

Specifications of EVAL-ADXL343Z-M

• Rohs: yes
• Tool Is For Evaluation Of: ADXL343
• Acceleration: 2 g, 4 g, 8 g, 16 g
• Sensing Axis: Triple Axis
• Interface Type: I2C, SPI
• Operating Voltage: 2 V to 3.6 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Operating Current: 140 uA
• Output Type: Digital
• Product: Evaluation Systems
• Sensitivity: 256 LSB/g, 128 LSB/g, 64 LSB/g, 32 LSG/g
• Factory Pack Quantity: 1

Data Sheet
USING SELF-TEST
The self-test change is defined as the difference between the
acceleration output of an axis with self-test enabled and the
acceleration output of the same axis with self-test disabled (see
Endnote 4 of Table 1). This definition assumes that the sensor
does not move between these two measurements. If the sensor
moves, the additional shift, which is unrelated to self-test,
corrupts the test.
Proper configuration of the
accurate self-test measurement. The part should be set with a
data rate of 100 Hz through 800 Hz, or 3200 Hz. This is done by
ensuring that a value of 0x0A through 0x0D, or 0x0F is written
into the rate bits (Bit D3 through Bit D0) in the BW_RATE
register (Address 0x2C). The part also must be placed into
normal power operation by ensuring the LOW_POWER bit in
the BW_RATE register is cleared (LOW_POWER bit = 0) for
accurate self-test measurements. It is recommended that the
part be set to full-resolution, 16 g mode to ensure that there is
sufficient dynamic range for the entire self-test shift. This is done
by setting Bit D3 of the DATA_FORMAT register (Address 0x31)
and writing a value of 0x03 to the range bits (Bit D1 and Bit D0) of
the DATA_FORMAT register (Address 0x31). This results in a high
dynamic range for measurement and a 3.9 mg/LSB scale factor.
After the part is configured for accurate self-test measurement,
several samples of x-, y-, and z-axis acceleration data should be
retrieved from the sensor and averaged together. The number
of samples averaged is a choice of the system designer, but a
recommended starting point is 0.1 sec worth of data for data
rates of 100 Hz or greater. This corresponds to 10 samples at
the 100 Hz data rate. For data rates less than 100 Hz, it is
recommended that at least 10 samples be averaged together. The
averaged values should be stored and labeled appropriately as
the self-test disabled data, that is, X
ADXL343
ST_OFF
is also necessary for an
, Y
ST_OFF
, and Z
ST_OFF
.
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Next, self-test should be enabled by setting Bit D7 (SELF_TEST) of
the DATA_FORMAT register (Address 0x31). The output needs
some time (about four samples) to settle after enabling self-test.
After allowing the output to settle, several samples of the x-, y-,
and z-axis acceleration data should be taken again and averaged. It
is recommended that the same number of samples be taken for
this average as was previously taken. These averaged values should
again be stored and labeled appropriately as the value with self-
test enabled, that is, X
disabled by clearing Bit D7 (SELF_TEST) of the DATA_FORMAT
register (Address 0x31).
With the stored values for self-test enabled and disabled, the
self-test change is as follows:
Because the measured output for each axis is expressed in LSBs,
X
converted to g’s of acceleration by multiplying each value by the
3.9 mg/LSB scale factor, if configured for full-resolution mode.
Additionally, Table 15 through Table 18 correspond to the self-test
range converted to LSBs and can be compared with the measured
self-test change when operating at a V
the minimum and maximum self-test output values should be
adjusted based on (multiplied by) the scale factors shown in
Table 14. If the part was placed into ±2 g, 10-bit or full-resolution
mode, the values listed in Table 15 should be used. Although
the fixed 10-bit mode or a range other than 16 g can be used, a
different set of values, as indicated in Table 16 through Table 18,
would need to be used. Using a range below 8 g may result in
insufficient dynamic range and should be considered when
selecting the range of operation for measuring self-test.
If the self-test change is within the valid range, the test is considered
successful. Generally, a part is considered to pass if the minimum
magnitude of change is achieved. However, a part that changes
by more than the maximum magnitude is not necessarily a failure.
Another effective method for using the self-test to verify accel-
erometer functionality is to toggle the self-test at a certain rate
and then perform an FFT on the output. The FFT should have a
corresponding tone at the frequency the self-test was toggled.
Using an FFT like this removes the dependency of the test on
supply voltage and on self-test magnitude, which can vary within
a rather wide range.
ST
, Y
X
Y
Z
ST
ST
ST
ST
, and Z
= Y
= Z
= X
ST_ON
ST_ON
ST_ON
ST
are also expressed in LSBs. These values can be
− Y
− Z
− X
ST_OFF
ST_OFF
ST_ON
ST_OFF
, Y
ST_ON
, and Z
S
of 2.5 V. For other voltages,
ST_ON
. Self-test can then be
ADXL343