EVAL-ADXL346Z Analog Devices Inc, EVAL-ADXL346Z Datasheet - Page 29

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EVAL-ADXL346Z

Manufacturer Part Number
EVAL-ADXL346Z
Description
Inertial Sensor Evaluation System
Manufacturer
Analog Devices Inc
Datasheets

Specifications of EVAL-ADXL346Z

Silicon Manufacturer
Analog Devices
Silicon Core Number
ADXL346
Kit Application Type
Sensing - Motion / Vibration / Shock
Application Sub Type
Accelerometer
Silicon Family Name
IMEMS
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
APPLICATIONS INFORMATION
POWER SUPPLY DECOUPLING
A 1 μF tantalum capacitor (C
(C
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 V
may be helpful. Additionally, increasing the bypass capacitance
on V
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 V
V
the V
supplies as previously mentioned may be necessary.
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 44, 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.
DD I/O
INTERRUPT
I/O
CONTROL
) at V
S
S
to a 10 μF tantalum capacitor in parallel with a 0.1 μF
be separate supplies to minimize digital clock noise on
supply. If this is not possible, additional filtering of the
DD I/O
Figure 44. Incorrectly Placed Accelerometers
placed close to the ADXL346 supply pins is
C
MOUNTING POINTS
S
Figure 43. Applications Diagram
ACCELEROMETERS
INT1
INT2
V
V
S
S
SDO/ALT ADDRESS
ADXL346
PCB
S
GND
) at V
SDA/SDI/SDIO
S
. It is recommended that V
SCL/SCLK
V
V
S
DD I/O
DD I/O
and a 0.1 μF ceramic capacitor
CS
C
I/O
3-WIRE OR
4-WIRE SPI
OR I
INTERFACE
2
C
S
and
Rev. A | Page 29 of 40
S
TAP DETECTION
The tap interrupt function is capable of detecting either single
or double taps. The following parameters are shown in Figure 45
for a valid single-tap event and a valid double-tap event:
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
register (Address 0x2A) is set, any acceleration spike above the
threshold during the latency time (set by the latent register)
invalidates the double-tap detection, as shown in Figure 46.
Figure 45. Tap Interrupt Function with Valid Single and Double Taps
The tap detection threshold is defined by the THRESH_TAP
register (Address 0x1D).
The maximum tap duration time is defined by the DUR
register (Address 0x21).
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.
LATENCY
(LATENT)
TIME
FIRST TAP
TIME LIMIT FOR
SINGLE-TAP
INTERRUPT
TAPS (DUR)
SECOND TAP (WINDOW)
TIME WINDOW FOR
SECOND TAP
DOUBLE-TAP
INTERRUPT
THRESHOLD
(THRESH_TAP)
ADXL346

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