ADXL375

Data Sheet

Rev. 0 | Page 10 of 32

THEORY OF OPERATION

The ADXL375 is a complete 3-axis acceleration measurement

system with a measurement range of ±200 g. It measures both

dynamic acceleration resulting from motion or shock and static

acceleration, such as gravity.

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 resistance

against forces due to applied acceleration.

Deflection of the structure is measured using differential capac-

itors 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

damaging the ADXL375. Table 7 provides a description of all

the power modes. The interface voltage level is set using the

that the ADXL375 does not create a conflict on the communi-

mode, power consumption is minimized; the device waits for

mode. This command can be initiated by setting the measure bit

(Bit D3) in the POWER_CTL register (Address 0x2D).

When the device is in standby mode, any register can be written

to or read from. It is recommended that the device be configured

in standby mode before enabling measurement mode. Clearing

the measure bit returns the device to standby mode.

CURRENT CONSUMPTION AND OUTPUT DATA RATE

The ADXL375 automatically modulates its current consumption

in proportion to its output data rate (see Table 6). The device

bandwidth and output data rate are specified using the rate bits

(Bits[D3:D0]) in the BW_RATE register (Address 0x2C).

Table 6. Typical Current Consumption vs. Data Rate

Rate Bits

Output Data

Rate (Hz)

Bandwidth

(Hz)

1111

3200

1600

145

1110

1600

800

90

1101

800

400

140

1100

400

200

140

1011

200

100

140

1010

100

50

140

1001

50

25

90

1000

25

12.5

60

0111

12.5

6.25

50

0110

6.25

3.13

40

0101

3.13

1.56

35

0100

1.56

0.78

35

0011

0.78

0.39

35

0010

0.39

0.20

35

0001

0.20

0.10

35

0000

0.10

0.05

35

Table 7. Power Modes

Power Mode

Description

Power Off

Off

Off

The device is completely off, but it is still possible for the device to create a conflict on the

communication bus.

Bus Disabled

On

Off

The device is on in standby mode, but communication is unavailable and the device can create

a conflict on the communication bus. Minimize the duration of the bus disabled state during

power-up to prevent a conflict on the communication bus.

Bus Enabled

Off

On

No functions are available, but the device does not create a conflict on the communication bus.

Standby or Measurement

On

On

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.