ADXL346ACCZ-R2 datasheet(29/40 Pages) AD

29 / 40 page

Data Sheet

ADXL346

APPLICATIONS INFORMATION

POWER SUPPLY DECOUPLING

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

(CI/O) at VDD I/O placed close to the ADXL346 supply pins is

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.

Care should be taken to ensure that the connection from the

ADXL346 ground to the power supply ground has low impedance

because noise transmitted 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 clock noise on

the VS supply. If this is not possible, additional filtering of the

supplies as previously mentioned may be necessary.

ADXL346

GND

INT1

INT2

SCL/SCLK

SDO/ALT ADDRESS

SDA/SDI/SDIO

3-WIRE OR

4-WIRE SPI

OR I2C

INTERFACE

VDD I/O

CI/O

INTERRUPT

CONTROL

Figure 44. Applications Diagram

MECHANICAL CONSIDERATIONS FOR MOUNTING

The ADXL346 should be mounted on the PCB in a location

close to a hard mounting point of the PCB to the case. Mounting

the ADXL346 at an unsupported PCB location, as shown in

Figure 45, 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 accelerometer’s mechanical sensor

resonant frequency and, therefore, effectively invisible to the

accelerometer. Multiple mounting points, close to the sensor,

and/or a thicker PCB also help to reduce the effect of system

resonance on the performance of the sensor.

MOUNTING POINTS

PCB

ACCELEROMETERS

Figure 45. Incorrectly Placed Accelerometers

TAP DETECTION

The tap interrupt function is capable of detecting either single

or double taps. The following parameters are shown in Figure 46

for a valid single-tap event and a valid double-tap event:

•

The tap detection threshold is defined by the THRESH_TAP

•

The maximum tap duration time is defined by the DUR

•

The tap latency time is defined by the latent register

(Address 0x22) and is the waiting period from the end of

the first tap until the start of the time window when a

second tap can be detected, which is determined by the

value in the window register (Address 0x23).

•

The interval after the latency time (set by the latent register) is

defined by the window register. Although a second tap must

begin after the latency time has expired, it need not finish

before the end of the time defined by the window register.

FIRST TAP

TIME LIMIT FOR

TAPS (DUR)

LATENCY

TIME

(LATENT)

TIME WINDOW FOR

SECOND TAP (WINDOW)

SECOND TAP

SINGLE-TAP

INTERRUPT

DOUBLE-TAP

INTERRUPT

THRESHOLD

(THRESH_TAP)

Figure 46. Tap Interrupt Function with Valid Single and Double Taps

If only the single-tap function is in use, the single-tap interrupt

is triggered when the acceleration goes below the threshold, as

long as DUR has not been exceeded. If both single and double-

tap functions are in use, the single-tap interrupt is triggered

when the double-tap event has been either validated or

invalidated.

Several events can occur to invalidate the second tap of a

double-tap event. First, if the suppress bit in the TAP_AXES

threshold during the latency time (set by the latent register)

invalidates the double-tap detection, as shown in Figure 47.

Rev. C | Page 29 of 40

ADXL346ACCZ-R2 データシート(PDF) 29 Page - Analog Devices

ADXL346ACCZ-R2 データシート(HTML) 29 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 33 34 35 36 37 38 39 40

データシートダウンロード

リンク URL

ADXL346ACCZ-R2 データシート(PDF) 29 Page - Analog Devices

ADXL346ACCZ-R2 データシート(HTML) 29 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 33 34 35 36 37 38 39 40

データシート ダウンロード

リンク URL

データシートダウンロード