ADXL345BCCZ-RL Ver la hoja de datos (PDF) - Analog Devices
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ADXL345BCCZ-RL Datasheet PDF : 40 Pages
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Data Sheet
NOISE PERFORMANCE
The specification of noise shown in Table 1 corresponds to
the typical noise performance of the ADXL345 in normal power
operation with an output data rate of 100 Hz (LOW_POWER bit
(D4) = 0, rate bits (D3:D0) = 0xA in the BW_RATE register,
Address 0x2C). For normal power operation at data rates below
100 Hz, the noise of the ADXL345 is equivalent to the noise at 100
Hz ODR in LSBs. For data rates greater than 100 Hz, the noise
increases roughly by a factor of √2 per doubling of the data rate.
For example, at 400 Hz ODR, the noise on the x- and y-axes is
typically less than 1.5 LSB rms, and the noise on the z-axis is
typically less than 2.2 LSB rms.
For low power operation (LOW_POWER bit (D4) = 1 in the
BW_RATE register, Address 0x2C), the noise of the ADXL345 is
constant for all valid data rates shown in Table 8. This value is
typically less than 1.8 LSB rms for the x- and y-axes and typically
less than 2.6LSB rms for the z-axis.
The trend of noise performance for both normal power and low
power modes of operation of the ADXL345 is shown in Figure 51.
Figure 52 shows the typical Allan deviation for the ADXL345.
The 1/f corner of the device, as shown in this figure, is very low,
allowing absolute resolution of approximately 100 µg (assuming
that there is sufficient integration time). Figure 52 also shows
that the noise density is 290 µg/√Hz for the x-axis and y-axis
and 430 µg/√Hz for the z-axis.
Figure 53 shows the typical noise performance trend of the
ADXL345 over supply voltage. The performance is normalized
to the tested and specified supply voltage, VS = 2.5 V. In general,
noise decreases as supply voltage is increased. It should be noted, as
shown in Figure 51, that the noise on the z-axis is typically higher
than on the x-axis and y-axis; therefore, while they change roughly
the same in percentage over supply voltage, the magnitude of change
on the z-axis is greater than the magnitude of change on the
x-axis and y-axis.
5.0
4.5
X-AXIS, LOW POWER
Y-AXIS, LOW POWER
4.0
Z-AXIS, LOW POWER
X-AXIS, NORMAL POWER
Y-AXIS, NORMAL POWER
3.5
Z-AXIS, NORMAL POWER
3.0
2.5
2.0
1.5
1.0
0.5
0
3.13 6.25 12.50 25 50 100 200 400 800 1600 3200
OUTPUT DATA RATE (Hz)
Figure 51. Noise vs. Output Data Rate for Normal and Low Power Modes,
Full-Resolution (256 LSB/g)
10k
X-AXIS
Y-AXIS
Z-AXIS
1k
ADXL345
100
10
0.01
0.1
1
10
100
1k
10k
AVERAGING PERIOD, (s)
Figure 52. Root Allan Deviation
130
120
X-AXIS
110
Y-AXIS
Z-AXIS
100
90
80
70
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
SUPPLY VOLTAGE, VS (V)
Figure 53. Normalized Noise vs. Supply Voltage, VS
OPERATION AT VOLTAGES OTHER THAN 2.5 V
The ADXL345 is tested and specified at a supply voltage of
VS = 2.5 V; however, it can be powered with VS as high as 3.6 V
or as low as 2.0 V. Some performance parameters change as the
supply voltage changes: offset, sensitivity, noise, self-test, and
supply current.
Due to slight changes in the electrostatic forces as supply voltage
is varied, the offset and sensitivity change slightly. When operating
at a supply voltage of VS = 3.3 V, the x- and y-axis offset is typically
25 mg higher than at Vs = 2.5 V operation. The z-axis is typically
20 mg lower when operating at a supply voltage of 3.3 V than when
operating at VS = 2.5 V. Sensitivity on the x- and y-axes typically
shifts from a nominal 256 LSB/g (full-resolution or ±2 g, 10-bit
operation) at VS = 2.5 V operation to 265 LSB/g when operating
with a supply voltage of 3.3 V. The z-axis sensitivity is unaffected by
a change in supply voltage and is the same at VS = 3.3 V operation
as it is at VS = 2.5 V operation. Simple linear interpolation can be
used to determine typical shifts in offset and sensitivity at other
supply voltages.
Rev. E | Page 33 of 40
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