ADXL312ACPZ-RL データシートの表示（PDF） - Analog Devices
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ADXL312ACPZ-RL Datasheet PDF : 32 Pages
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ADXL312
THEORY OF OPERATION
The ADXL312 is a complete 3-axis acceleration measurement
system with a selectable measurement range of ±1.5 g, ±3 g, ±6
g, or ±12 g. It measures both dynamic acceleration resulting
from motion or shock and static acceleration, such as gravity,
which allows it to be used as a tilt sensor.
The sensor is a polysilicon surface-micromachined structure
built on top of a silicon wafer. Polysilicon springs suspend the
structure over the surface of the wafer and provide a resistance
against acceleration forces.
Deflection of the structure is measured using differential
capacitors that consist of independent fixed plates and plates
attached to the moving mass. Acceleration deflects the beam
and unbalances the differential capacitor, resulting in a sensor
output whose amplitude is proportional to acceleration. Phase-
sensitive demodulation is used to determine the magnitude and
polarity of the acceleration.
POWER SEQUENCING
Power can be applied to VS or VDD I/O in any sequence without
damaging the ADXL312. All possible power-on modes are
summarized in Table 5. The interface voltage level is set with
the interface supply voltage, VDD I/O, which must be present to
ensure that the ADXL312 does not create a conflict on the
communication bus. For single-supply operation, VDD I/O can be
the same as the main supply, VS. In a dual-supply application,
however, VDD I/O can differ from VS to accommodate the desired
interface voltage, as long as VS is greater than or equal to VDD I/O.
After VS is applied, the device enters standby mode, where power
consumption is minimized and the device waits for VDD I/O to be
applied and for the command to enter measurement mode to be
received. (This command can be initiated by setting the measure
bit in the POWER_CTL register (Address 0x2D).) In addition, any
register can be written to or read from to configure the part while
the device is in standby mode. It is recommended to configure the
device in standby mode and then to enable measurement mode.
Clearing the measure bit returns the device to the standby mode.
Table 5. Power Sequencing
Condition
VS VDD I/O
Power Off
Off Off
Bus Disabled On Off
Bus Enabled Off On
Standby or On On
Measurement
Description
The device is completely off, but
there is a potential for a
communication bus conflict.
The device is on in standby mode,
but communication is unavailable
and will create a conflict on the
communication bus. The duration
of this state should be minimized
during power-up to prevent a
conflict.
No functions are available, but
the device will not create a conflict
on the communication bus.
The device is in standby mode,
awaiting a command to enter
measurement mode, and all sensor
functions are off. After the device is
instructed to enter measurement
mode, all sensor functions are
available.
POWER SAVINGS
Power Modes
The ADXL312 automatically modulates its power consumption
in proportion to its output data rate, as outlined in Table 6. If
additional power savings is desired, a lower power mode is
available. In this mode, the internal sampling rate is reduced,
allowing for power savings in the 12.5 Hz to 400 Hz data rate
range at the expense of slightly greater noise. To enter low
power mode, set the LOW_POWER bit (Bit 4) in the BW_RATE
register (Address 0x2C). The current consumption in low power
mode is shown in Table 7 for cases where there is an advantage
to using low power mode. Use of low power mode for a data
rate not shown in Table 7 does not provide any advantage over
the same data rate in normal power mode. Therefore, it is
recommended that only data rates shown in Table 7 be used in
low power mode. The current consumption values shown in
Table 6 and Table 7 are for a VS of 3.3 V.
Rev. 0 | Page 10 of 32
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