ADXL346ACCZ(RevPrC) 데이터 시트보기 (PDF) - Analog Devices

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ADXL346ACCZ
(Rev.:RevPrC)

3-Axis, ±2 g/±4 g/±8 g/±16 g Ultralow Power Digital Accelerometer

Analog Devices 

ADXL346

Preliminary Technical Data

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

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 ADXL346. 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 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 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

Power Off

VS

VDD I/O

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.

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.

POWER SAVINGS

Power Modes

The ADXL346 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. The current consumption values

shown in Table 6 and Table 7 are for a VS of 2.5 V.

Table 6. Typical Current Consumption vs. Data Rate

(TA = 25°C, VS = 2.5 V, VDD I/O = 1.8 V)

Output Data

Rate (Hz)

Bandwidth (Hz)

Rate Code IDD (µA)

3200

1600

1111

140

1600

800

1110

90

800

400

1101

140

400

200

1100

140

200

100

1011

140

100

50

1010

140

50

25

1001

90

25

12.5

1000

60

12.5

6.25

0111

45

6.25

3.125

0110

35

Table 7. Typical Current Consumption vs. Data Rate, Low

Power Mode (TA = 25°C, VS = 2.5 V, VDD I/O = 1.8 V)

Output Data

Rate (Hz)

Bandwidth (Hz) Rate Code IDD (µA)

400

200

1100

90

200

100

1011

60

100

50

1010

45

50

25

1001

35

25

12.5

1000

35

12.5

6.25

0111

35

Rev. PrC | Page 10 of 32

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