ADXL312WACPZ-RL Analog Devices Inc, ADXL312WACPZ-RL Datasheet - Page 25

• Manufacturer Part Number: ADXL312WACPZ-RL
• Description: IC ACCEL SPI/I2C 3AX 32LFCSP
• Manufacturer: Analog Devices Inc

Specifications of ADXL312WACPZ-RL

• Axis: X, Y, Z
• Acceleration Range: ±1.5g, 3g, 6g, 12g
• Sensitivity: 345LSB/g, 172LSB/g, 86LSB/g, 43LSB/g
• Voltage - Supply: 2 V ~ 3.6 V
• Output Type: Digital
• Bandwidth: 6.25 Hz ~ 3200 Hz
• Interface: I²C, SPI
• Mounting Type: Surface Mount
• Package / Case: 32-LFQFN, CSP Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
POWER SUPPLY DECOUPLING
A 1 μF tantalum capacitor (C
(C
recommended to adequately decouple the accelerometer from
noise on the power supply. If additional decoupling is necessary,
a resistor or ferrite bead, no larger than 100 Ω, in series with V
may be helpful. Additionally, increasing the bypass capacitance
on V
ceramic capacitor may also improve noise.
Care should be taken to ensure that the connection from the
ADXL312 ground to the power supply ground has low impedance
because noise transmitted through ground has an effect similar
to noise transmitted through V
V
on the V
the supplies as previously mentioned may be necessary.
MECHANICAL CONSIDERATIONS FOR MOUNTING
The ADXL312 should be mounted on the PCB in a location
close to a hard mounting point of the PCB to the case. Mounting
the ADXL312 at an unsupported PCB location, as shown in
Figure 31, may result in large, apparent measurement errors due
to undampened PCB vibration. Locating the accelerometer near
a hard mounting point ensures that any PCB vibration at the
accelerometer is above the accelerometer’s mechanical sensor
resonant frequency and, therefore, effectively 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.
DD I/O
INTERRUPT
I/O
CONTROL
) at V
S
to a 10 μF tantalum capacitor in parallel with a 0.1 μF
be separate supplies to minimize digital clocking noise
S
supply. If this is not possible, additional filtering of
DD I/O
Figure 31. Incorrectly Placed Accelerometers
placed close to the ADXL312 supply pins is
MOUNTING POINTS
C
S
Figure 30. Application Diagram
ACCELEROMETERS
INT1
INT2
V
V
S
S
SDO/ALT ADDRESS
ADXL312
PCB
S
GND
) at V
SDA/SDI/SDIO
S
SCL/SCLK
. It is recommended that V
V
V
DD I/O
DD I/O
S
and a 0.1 μF ceramic capacitor
CS
C
I/O
3-WIRE OR
4-WIRE SPI
OR I
INTERFACE
2
C
S
and
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S
THRESHOLD
The lower output data rates are achieved by decimating a
common sampling frequency inside the device. The activity
detection function is performed using undecimated data.
Because the bandwidth of the output data varies with the data
rate and is lower than the bandwidth of the undecimated data,
the high frequency and high g data that are used to determine
activity may not be present if the output of the accelerometer is
examined. This may result in functions triggering when
acceleration data does not appear to meet the conditions set by
the user for the corresponding function.
LINK MODE
The function of the link bit is to reduce the number of activity
interrupts that the processor must service by setting the device
to look for activity only after inactivity. For proper operation of
this feature, the processor must still respond to the activity and
inactivity interrupts by reading the INT_SOURCE register
(Address 0x30) and, therefore, clearing the interrupts. If an activity
interrupt is not cleared, the part cannot go into autosleep mode.
SLEEP MODE VS. LOW POWER MODE
In applications where a low data rate and low power consumption
are desired (at the expense of noise performance), it is
recommended that low power mode be used. The use of low
power mode preserves the functionality of the DATA_READY
interrupt and the FIFO for postprocessing of the acceleration
data. Sleep mode, while offering a low data rate and power
consumption, is not intended for data acquisition.
However, when sleep mode is used in conjunction with the
autosleep mode and the link mode, the part can automatically
switch to a low power, low sampling rate mode when inactivity
is detected. To prevent the generation of redundant inactivity
interrupts, the inactivity interrupt is automatically disabled
and activity is enabled. When the ADXL312 is in sleep mode, the
host processor can also be placed into sleep mode or low power
mode to save significant system power. Once activity is
detected, the accelerometer automatically switches back to the
original data rate of the application and provides an activity
interrupt that can be used to wake up the host processor.
Similar to when inactivity occurs, detection of activity events is
disabled and inactivity is enabled.
ADXL312