EVAL-ADXL345Z-M Analog Devices Inc, EVAL-ADXL345Z-M Datasheet - Page 33

• Manufacturer Part Number: EVAL-ADXL345Z-M
• Description: BOARD EVAL FOR ADXL345
• Manufacturer: Analog Devices Inc
• Series: iMEMS®r

Specifications of EVAL-ADXL345Z-M

• Sensor Type: Accelerometer, 3 Axis
• Sensing Range: ±2g, 4g, 8g, 16g
• Interface: I²C, SPI
• Sensitivity: 256 LSB/g
• Voltage - Supply: 1.8 V ~ 3.6 V
• Embedded: No
• Utilized Ic / Part: ADXL345
• Silicon Manufacturer: Analog Devices
• Application Sub Type: Accelerometer - Three-Axis
• Kit Application Type: Sensing - Motion / Vibration / Shock
• Silicon Core Number: ADXL345
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 50.
Figure 51 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 51 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 52 shows the typical noise performance trend of the
ADXL345 over supply voltage. The performance is normalized
to the tested and specified supply voltage, V
noise decreases as supply voltage is increased. It should be noted, as
shown in Figure 50, 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.
Figure 50. Noise vs. Output Data Rate for Normal and Low Power Modes,
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
3.13 6.25 12.50 25
X-AXIS, LOW POWER
Y-AXIS, LOW POWER
Z-AXIS, LOW POWER
X-AXIS, NORMAL POWER
Y-AXIS, NORMAL POWER
Z-AXIS, NORMAL POWER
Full-Resolution (256 LSB/g)
OUTPUT DATA RATE (Hz)
50
100 200
400 800 1600 3200
S
= 2.5 V. In general,
Rev. B | Page 33 of 40
OPERATION AT VOLTAGES OTHER THAN 2.5 V
The ADXL345 is tested and specified at a supply voltage of
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 V
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 V
shifts from a nominal 256 LSB/g (full-resolution or ±2 g, 10-bit
operation) at V
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 V
as it is at V
used to determine typical shifts in offset and sensitivity at other
supply voltages.
S
= 2.5 V; however, it can be powered with V
10k
100
130
120
100
110
1k
10
90
80
70
0.01
2.0
S
Figure 52. Normalized Noise vs. Supply Voltage, V
= 2.5 V operation. Simple linear interpolation can be
S
2.2
S
= 2.5 V. Sensitivity on the x- and y-axes typically
0.1
= 2.5 V operation to 265 LSB/g when operating
Figure 51. Root Allan Deviation
2.4
S
AVERAGING PERIOD,
= 3.3 V, the x- and y-axis offset is typically
X-AXIS
Y-AXIS
Z-AXIS
SUPPLY VOLTAGE, V
1
2.6
X-AXIS
Y-AXIS
Z-AXIS
10
2.8
3.0
S
100
(V)
(s)
3.2
S
= 3.3 V operation
S
as high as 3.6 V
1k
ADXL345
3.4
S
10k
3.6