ADXL346ACCZ-R2 datasheet(12/40 Pages) AD

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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

VDDI/O

Description

Power Off

Off

The device is completely off, but there is a potential for a communication

bus conflict.

Bus Disabled

Off

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.

Bus Enabled

Off

No functions are available, but the device will not create a conflict on the

communication bus.

Standby or

Measurement Mode

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

ADXL346ACCZ-R2 Datasheet(PDF) 12 Page - Analog Devices

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