Data Sheet
ADXL36±
USING AN EXTERNAL CLOCK
OPERATION AT VOLTAGES OTHER THAN 2.0 V
The ADXL362 has a built-in clock that, by default, is used for
clocked internal operations. If desired, an external clock can be
provided and used.
The ADXL362 is tested and specified at a supply voltage of VS =
2.0 V; however, it can be powered with a VS as high as 3.3 V
nominal (3.5 V maximum) or as low as 1.8 V nominal (1.6 V
minimum). Some performance parameters change as the supply
voltage changes, including the supply current (see Figure 30),
noise (see Table 7 and Table 8), offset, sensitivity, and self test
output change (see Table 22).
To use an external clock, the EXT_CLK bit (Bit 6) in the
POWER_CTL register (Address 0x2D) must be set. Setting
this bit reconfigures the INT1 pin to an input pin on which the
clock can be provided. The external clock must operate at or
below 51.2 kHz. Further information is provided in the External
Clock section.
Figure 48 shows the potential effect on 0 g offset at varying
supply voltage. Data for this figure was calibrated to show 0 mg
offset at 2.0 V.
USING SELF TEST
200
The self test function, described in the Self Test section, is
enabled via the ST bit in the SELF_TEST register, Address 0x2E.
The recommended procedure for using the self test functionality is
as follows:
X-AXIS
Y-AXIS
Z-AXIS
150
100
50
1. Read acceleration data for the x-, y-, and z-axes.
2. Assert self test by setting the ST bit in the SELF_TEST
register, Address 0x2E.
3. Wait 1/ODR for the output to settle to its new value.
4. Read acceleration data for the x-, y-, and z-axes.
5. Compare to the values from Step 1, and convert the
difference from LSB to mg by multiplying by the sensitivity.
If the observed difference falls within the self test output
change specification listed in Table 1, then the device
passes self test and is deemed operational.
0
–50
–100
1.5
2.0
2.5
3.0
3.5
V
(V)
S
Figure 48. 0 g Offset vs. Supply Voltage
6. Deassert self test by clearing the ST bit in the SELF_TEST
register, Address 0x2E.
MECHANICAL CONSIDERATIONS FOR MOUNTING
Mount the ADXL362 on the printed circuit board (PCB) in a
location close to a hard mounting point of the PCB to the case.
Mounting the ADXL362 at an unsupported PCB location, as
shown in Figure 49, can result in large, apparent measurement
errors due to undampened PCB vibration. Locating the accel-
erometer near a hard mounting point ensures that any PCB
vibration at the accelerometer is above the mechanical sensor
resonant frequency of the accelerometer and, therefore, effec-
tively invisible to the accelerometer. Multiple mounting points,
close to the sensor, and/or a thicker PCB also help to reduce the
effect of system resonance on the performance of the sensor.
The self test output change specification is given for VS = 2.0 V.
Because the electrostatic force is proportional to VS2 and the
sensitivity of the device is ratiometric to VS, the output change
varies with VS. The scale factors shown in Table 22 can be used
to adjust the expected self test output limits for different supply
voltages, VS.
Note that at higher voltages, self test deltas may exceed 1 g. If
the measurement is performed with one axis experiencing 1 g
due to gravity, and if the accelerometer is configured for a 2 g
measurement range, the axis that is aligned with the field of
gravity may reach 2 g and its output clips (saturates to its full-
scale value). To alleviate this, self test can be measured with the
y-axis aligned with gravity (where the y-axis self test output
change is negative), or with the accelerometer configured for a
4 g or 8 g measurement range.
ACCELEROMETERS
PCB
MOUNTING POINTS
Table 22. Self Test Output Scale Factors for Different Supply
Voltages, VS
Figure 49. Incorrectly Placed Accelerometers
Supply Voltage, VS (V)
Self Test Output Scale Factor
1.6
2.0
2.5
3.0
3.5
0.62
1.0
1.6
2.4
3.4
Rev. B | Page 41 of 44
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