ADXL375 datasheet(26/32 Pages) AD

26 / 32 page

ADXL375

Data Sheet

Rev. 0 | Page 26 of 32

APPLICATIONS INFORMATION

POWER SUPPLY DECOUPLING

A 1 µF tantalum capacitor (CS) at VS and a 0.1 µF ceramic capac-

itor (CI/O) at VDD I/O placed close to the ADXL375 supply pins are

recommended to adequately decouple the accelerometer from

noise on the power supply. If additional decoupling is necessary,

a resistor or ferrite bead (no larger than 100 Ω) in series with VS

may be helpful. Additionally, increasing the bypass capacitance

on VS to a 10 µF tantalum capacitor in parallel with a 0.1 µF

ceramic capacitor may also improve noise performance.

Make sure that the connection from the ADXL375 ground to

the power supply ground has low impedance because noise trans-

mitted through ground has an effect similar to noise transmitted

through VS. It is recommended that VS and VDD I/O be separate

supplies to minimize digital clocking noise on the VS supply. If

it is not possible to use separate supplies, additional filtering of

the supplies, as previously mentioned, may be necessary.

ADXL375

GND

INT1

INT2

SCL/SCLK

SDO/ALT ADDRESS

SDA/SDI/SDIO

3- OR 4-WIRE

SPI OR I2C

INTERFACE

VDD I/O

CI/O

INTERRUPT

CONTROL

Figure 31. Application Diagram

MECHANICAL CONSIDERATIONS FOR MOUNTING

Mount the ADXL375 on the PCB in a location close to a hard

mounting point of the PCB to the case. Mounting the ADXL375

at an unsupported PCB location, as shown in Figure 32, may result

in large, apparent measurement errors due to undampened PCB

vibration. Locating the accelerometer near a hard mounting point

ensures that any PCB vibration at the accelerometer is above the

mechanical sensor resonant frequency of the accelerometer and

is, therefore, effectively invisible to the accelerometer. Multiple

mounting points, close to the sensor, and/or a thicker PCB also

help to reduce the effects of system resonance on the performance

of the sensor.

MOUNTING POINTS

PCB

ACCELEROMETERS

Figure 32. Incorrectly Placed Accelerometers

SHOCK DETECTION

The shock interrupt function can detect mechanical shock events

based on amplitude and pulse width. Figure 33 illustrates the

following parameters for a valid single shock event and a valid

double shock event.

•

Shock detection threshold—defined by the THRESH_

SHOCK register (Address 0x1D).

•

Maximum shock duration time (time limit for shocks)—

defined by the DUR register (Address 0x21).

•

Shock latency time—defined by the latent register (Address

0x22). The latency time is the waiting period from the end

of the first shock until the start of the time window, when a

second shock can be detected.

•

Time window for second shock—defined by the window

after the latency time (set by the latent register). Although

a second shock must begin after the latency time expires, it

need not finish before the end of the time defined by the

window register.

FIRST SHOCK

TIME LIMIT FOR

SHOCKS (DUR)

LATENCY

TIME

(LATENT)

TIME WINDOW FOR

SECOND SHOCK

(WINDOW)

SECOND SHOCK

SINGLE SHOCK

INTERRUPT

DOUBLE SHOCK

INTERRUPT

THRESHOLD

(THRESH_SHOCK)

Figure 33. Shock Interrupt Function with Valid Single and Double Shocks

If only the single shock function is in use, the single shock

interrupt is triggered when the acceleration goes below the

threshold, as long as the duration time is not exceeded. If

both the single and double shock functions are in use, the

single shock interrupt is triggered when the double shock

event is either validated or invalidated.

ADXL375 Datasheet(PDF) 26 Page - Analog Devices

ADXL375 Datasheet(HTML) 26 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL