ADXL362BCCZ-R2 datasheet(41/44 Pages) AD

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Data Sheet

ADXL362

Rev. B | Page 41 of 44

USING AN EXTERNAL CLOCK

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.

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.

USING SELF TEST

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:

1. Read acceleration data for the x-, y-, and z-axes.

2. Assert self test by setting the ST bit in the SELF_TEST

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.

6. Deassert self test by clearing the ST bit in the SELF_TEST

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.

Table 22. Self Test Output Scale Factors for Different Supply

Voltages, VS

Supply Voltage, VS (V)

Self Test Output Scale Factor

1.6

0.62

2.0

1.0

2.5

1.6

3.0

2.4

3.5

3.4

OPERATION AT VOLTAGES OTHER THAN 2.0 V

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).

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.

–100

–50

100

150

200

1.5

2.0

2.5

3.0

3.5

X-AXIS

Y-AXIS

Z-AXIS

VS (V)

Figure 48. 0 g Offset vs. Supply Voltage

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.

MOUNTING POINTS

PCB

ACCELEROMETERS

Figure 49. Incorrectly Placed Accelerometers

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