ADXL346ACCZ-R2 datasheet(21/40 Pages) AD

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Data Sheet

ADXL346

Rev. C | Page 21 of 40

SELF-TEST

The ADXL346 incorporates a self-test feature that effectively

tests its mechanical and electronic systems simultaneously.

When the self-test function is enabled (via the SELF_TEST bit

(Bit D7 in the DATA_FORMAT register, Address 0x31), an

electrostatic force is exerted on the mechanical sensor. This

electrostatic force moves the mechanical sensing element in the

same manner as acceleration would, and it is additive to the

acceleration experienced by the device. This added electrostatic

force results in an output change in the x-, y-, and z-axes. Because

the electrostatic force is proportional to VS2, the output change

varies with VS. This effect is shown in Figure 43.

The scale factors listed in Table 14 can be used to adjust the

expected self-test output limits for different supply voltages, VS.

The self-test feature of the ADXL346 also exhibits a bimodal

behavior. However, the limits listed in Table 1 and Table 15 to

Table 18 are valid for both potential self-test values due to bi-

modality. Use of the self-test feature at data rates less than 100 Hz

or at 1600 Hz may yield values outside these limits. Therefore,

the part must be in normal power operation (LOW_POWER

bit = 0 in the BW_RATE register, Address 0x2C) and be placed

into a data rate of 100 Hz through 800 Hz or 3200 Hz for the

self-test function to operate correctly.

1.6

1.8

2.0

2.2

2.4

2.6

2.8

SUPPLY VOLTAGE, VS (V)

X-AXIS SELF-TEST HIGH LIMIT

X-AXIS SELF-TEST LOW LIMIT

Y-AXIS SELF-TEST HIGH LIMIT

Y-AXIS SELF-TEST LOW LIMIT

Z-AXIS SELF-TEST HIGH LIMIT

Z-AXIS SELF-TEST LOW LIMIT

–3

–2

–1

Figure 43. Self-Test Output Change Limits vs. Supply Voltage

Table 14. Self-Test Output Scale Factors for Different Supply

Voltages, VS

Supply Voltage, VS

X-, Y-Axes

Z-Axis

1.70 V

0.43

0.38

1.80 V

0.48

0.47

2.00 V

0.59

0.58

2.60 V

1.00

2.75 V

1.13

1.11

Table 15. Self-Test Output in LSB for ±2 g, 10-Bit or Full

Resolution (TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis

Min

Max

Unit

400

LSB

−400

−70

LSB

100

500

LSB

Table 16. Self-Test Output in LSB for ±4 g, 10-Bit Resolution

(TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis

Min

Max

Unit

200

LSB

−200

−35

LSB

250

LSB

Table 17. Self-Test Output in LSB for ±8 g, 10-Bit Resolution

(TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis

Min

Max

Unit

100

LSB

−100

−17

LSB

125

LSB

Table 18. Self-Test Output in LSB for ±16 g, 10-Bit Resolution

(TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis

Min

Max

Unit

LSB

−50

−8

LSB

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