ADXL346(RevC) Просмотр технического описания (PDF) - Analog Devices
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ADXL346 Datasheet PDF : 40 Pages
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ADXL346
Data Sheet
THEORY OF OPERATION
The ADXL346 is a complete 3-axis acceleration measurement
system with a selectable measurement range of ±2 g, ±4 g, ±8 g,
or ±16 g. It measures both dynamic acceleration resulting from
motion or shock and static acceleration, such as gravity, which
allows the device 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 forces due to applied acceleration.
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 proof mass and unbalances
the differential capacitor, resulting in a sensor output with an
amplitude proportional to acceleration. Phase-sensitive de-
modulation 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 ADXL346. All possible power-on modes are
summarized in Table 6. The interface voltage level is set with
the interface supply voltage, VDD I/O, which must be present to
ensure that the ADXL346 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 (Bit D3) 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 6. Power Sequencing
Condition
VS
Power Off
Off
Bus Disabled
On
Bus Enabled
Off
Standby or
On
Measurement Mode
VDD I/O
Off
Off
On
On
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.
At power-up, 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.
Rev. C | Page 12 of 40
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