ADXL322

Rev. 0 | Page 13 of 16

Peak-to-peak noise values give the best estimate of the uncer-

tainty in a single measurement. Table 7 gives the typical noise

Bandwidth

(Hz)

(μF)

RMS Noise

(mg)

Peak-to-Peak Noise

Estimate (mg)

10

0.47

0.9

5.3

50

0.1

2

11.8

100

0.047

2.8

16.7

500

0.01

6.2

37.3

USE WITH OPERATING VOLTAGES OTHER THAN 3 V

Note that some performance parameters change as the supply

voltage is varied.

The ADXL322 output is ratiometric, so the output sensitivity

the output sensitivity is typically 335 mV/g.

The zero g bias output is also ratiometric, so the zero g output is

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

the noise density is typically 300 μg/√Hz,

Self-test response in g is roughly proportional to the square of

the supply voltage. However, when ratiometricity of sensitivity

is factored in with supply voltage, the self-test response in volts

is roughly proportional to the cube of the supply voltage. For

approximately 59 mV.

The supply current decreases as the supply voltage decreases.

USE AS A DUAL-AXIS TILT SENSOR

Tilt measurement is one of the ADXL322’s most popular

applications. An accelerometer uses the force of gravity as an

input vector to determine the orientation of an object in space.

An accelerometer is most sensitive to tilt when its sensitive axis

is perpendicular to the force of gravity (that is, when the pack-

age is parallel to the earth’s surface). At this orientation, the

accelerometer’s sensitivity to changes in tilt is highest. When the

accelerometer is oriented on axis to gravity (near its +1 g or −1 g

reading), the change in output acceleration per degree of tilt is

negligible. When the accelerometer is perpendicular to gravity,

its output changes nearly 17.5 mg per degree of tilt. At 45°, its

output changes at only 12.2 mg per degree of tilt, and resolution

declines.

Converting Acceleration to Tilt

When the accelerometer is oriented so both its X-axis and

Y-axis are parallel to the earth’s surface, it can be used as a

2-axis tilt sensor with both a roll axis and a pitch axis. Once

the output signal from the accelerometer has been converted

to an acceleration that varies between −1 g and +1 g, the output

tilt in degrees is calculated as

Be sure to account for overranges. It is possible for the

accelerometers to output a signal greater than ±1 g due

to vibration, shock, or other accelerations.