EVAL-ADXL346Z - Analog Devices

3-Axis, ±2 g/±4 g/±8 g/±16 g

Ultralow Power Digital Accelerometer

Data Sheet ADXL346

Rev. C Document Feedback

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FEATURES

Ultralow power: as low as 23 μA in measurement mode and

0.2 μA in standby mode at VS = 2.6 V (typical)

Power consumption scales automatically with bandwidth

User-selectable resolution

Fixed 10-bit resolution

Full resolution, where resolution increases with g range,

up to 13-bit resolution at ±16 g (maintaining 4 mg/LSB

scale factor in all g ranges)

Embedded memory management system with FIFO

technology minimizes host processor load

Single tap/double tap detection

Activity/inactivity monitoring

Free-fall detection

Concurrent four- and six-position orientation detection

Supply and I/O voltage range: 1.7 V to 2.75 V

SPI (3- and 4-wire) and I2C digital interfaces

Flexible interrupt modes mappable to either interrupt pin

Measurement ranges selectable via serial command

Bandwidth selectable via serial command

Wide temperature range (−40°C to +85°C)

10,000 g shock survival

Pb free/RoHS compliant

Small and thin: 3 mm × 3 mm × 0.95 mm LGA package

APPLICATIONS

Handsets

Medical instrumentation

Gaming and pointing devices

Industrial instrumentation

Personal navigation devices

Hard disk drive (HDD) protection

GENERAL DESCRIPTION

The ADXL346 is a small, thin, ultralow power, 3-axis accelerometer

with high resolution (13-bit) measurement at up to ±16 g. Digital

output data is formatted as 16-bit twos complement and is acces-

sible through either an SPI (3- or 4-wire) or I2C digital interface.

The ADXL346 is well suited for mobile device applications. It

measures the static acceleration of gravity in tilt-sensing appli-

cations, as well as dynamic acceleration resulting from motion

or shock. Its high resolution (4 mg/LSB) enables measurement

of inclination changes of less than 1.0°.

Several special sensing functions are provided. Activity and

inactivity sensing detect the presence or lack of motion by

comparing the acceleration on any axis with user-set thresholds.

Tap sensing detects single and double taps in any direction. Free-

fall sensing detects if the device is falling. Orientation detection

is capable of concurrent four- and six-position sensing and a

user-selectable interrupt on orientation change for 2D or 3D

applications. These functions can be mapped individually to

either of two interrupt output pins. An integrated memory

management system with 32-level first in, first out (FIFO) buffer

can be used to store data to minimize host processor activity and

lower overall system power consumption.

Low power modes enable intelligent motion-based power

management with threshold sensing and active acceleration

measurement at extremely low power dissipation.

The ADXL346 is supplied in a small, thin, 3 mm × 3 mm ×

0.95 mm, 16-lead, plastic package.

FUNCTIONAL BLOCK DIAGRAM

3-AXIS

SENSOR

SENSE

ELECTRONICS DIGITAL

FILTER

ADXL346

POWER

MANAGEMENT

CONTROL

AND

INTERRUPT

LOGIC

SERIAL I/O

INT1

DD I/ O

INT2

SDA/SDI/SDIO

SDO/ALT

ADDRESS

SCL/SCLK

GND

ADC

32-LEVEL

FIFO

08167-001

Figure 1.

ADXL346 Data Sheet

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

General Description ......................................................................... 1

Functional Block Diagram .............................................................. 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

Absolute Maximum Ratings ............................................................ 5

Thermal Resistance ...................................................................... 5

Package Information .................................................................... 5

ESD Caution .................................................................................. 5

Pin Configuration and Function Descriptions ............................. 6

Typical Performance Characteristics ............................................. 7

Theory of Operation ...................................................................... 12

Power Sequencing ...................................................................... 12

Power Savings ............................................................................. 13

Serial Communications ................................................................. 14

SPI ................................................................................................. 14

I2C ................................................................................................. 17

Interrupts ..................................................................................... 19

FIFO ............................................................................................. 20

Self-Test ........................................................................................ 21

Applications Information .............................................................. 29

Power Supply Decoupling ......................................................... 29

Mechanical Considerations for Mounting .............................. 29

Tap Detection .............................................................................. 29

Improved Tap Detection ............................................................ 30

Tap Sign ....................................................................................... 30

Threshold .................................................................................... 31

Link Mode ................................................................................... 31

Sleep Mode vs. Low Power Mode............................................. 31

Offset Calibration ....................................................................... 31

Using Self-Test ............................................................................ 32

Orientation Sensing ................................................................... 32

Data Formatting of Upper Data Rates ..................................... 34

Noise Performance ..................................................................... 35

Operation at Voltages Other Than 2.6 V ................................ 36

Offset Performance at Lowest Data Rates ............................... 36

Axes of Acceleration Sensitivity ............................................... 37

Layout and Design Recommendations ................................... 38

Outline Dimensions ....................................................................... 39

Ordering Guide .......................................................................... 39

REVISION HISTORY

6/15—Rev. B to Rev. C

Changes to Features Section and General

Description Section .......................................................................... 1

Change to Figure 36 ....................................................................... 14

Change to FIFO Section ................................................................ 20

5/11—Rev. A to Rev. B

Added Endnote 7 .............................................................................. 3

Added Preventing Bus Traffic Errors Section ............................. 14

Changes to Figure 37, Figure 38, Figure 39 ................................. 15

Changes to Table 12 ........................................................................ 18

Changes to Using Self-Test Section .............................................. 32

Changes to Axes of Acceleration Sensitivity Section ................. 37

11/10—Rev. 0 to Rev. A

Changes to Ordering Guide .......................................................... 39

5/10—Revision 0: Initial Version

Rev. C | Page 2 of 40

Data Sheet ADXL346

Rev. C | Page 3 of 40

SPECIFICATIONS

TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V, acceleration = 0 g, CS = 10 μF tantalum, CI/O = 0.1 μF, ODR = 800 Hz, unless otherwise noted.

Table 1. Specifications

Parameter Test Conditions Min1 Typ2 Max1 Unit

SENSOR INPUT Each axis

Measurement Range User selectable ±2, ±4, ±8, ±16 g

Nonlinearity Percentage of full scale ±0.5 %

Inter-Axis Alignment Error ±0.1 Degrees

Cross-Axis Sensitivity3 ±1 %

OUTPUT RESOLUTION Each axis

All g Ranges 10-bit resolution 10 Bits

±2 g Range Full resolution 10 Bits

±4 g Range Full resolution 11 Bits

±8 g Range Full resolution 12 Bits

±16 g Range Full resolution 13 Bits

SENSITIVITY Each axis

Sensitivity at XOUT, YOUT, ZOUT All g ranges, full resolution 230 256 282 LSB/g

±2 g, 10-bit resolution 230 256 282 LSB/g

±4 g, 10-bit resolution 115 128 141 LSB/g

±8 g, 10-bit resolution 57 64 71 LSB/g

±16 g, 10-bit resolution 29 32 35 LSB/g

Sensitivity Deviation from Ideal All g ranges ±1.0 %

Scale Factor at XOUT, YOUT, ZOUT All g ranges, full resolution 3.5 3.9 4.3 mg/LSB

±2 g, 10-bit resolution 3.5 3.9 4.3 mg/LSB

±4 g, 10-bit resolution 7.1 7.8 8.7 mg/LSB

±8 g, 10-bit resolution 14.1 15.6 17.5 mg/LSB

±16 g, 10-bit resolution 28.6 31.2 34.5 mg/LSB

Sensitivity Change Due to Temperature ±0.02 %/°C

0 g OFFSET Each axis

0 g Output for XOUT, YOUT, ZOUT −150 0 +150 mg

0 g Output Deviation from Ideal ±35 mg

0 g Offset vs. Temperature for X-, Y-Axes ±0.7 mg/°C

0 g Offset vs. Temperature for Z-Axis ±1.3 mg/°C

NOISE

X-, Y-Axes ODR = 100 Hz for ±2 g, 10-bit

resolution or all g ranges, full

resolution

1.1 LSB rms

Z-Axis ODR = 100 Hz for ±2 g, 10-bit

resolution or all g ranges, full

resolution

1.5 LSB rms

OUTPUT DATA RATE AND BANDWIDTH User selectable

Output Data Rate (ODR)4, 5, 6, 7 0.10 3200 Hz

SELF-TEST8

Output Change in X-Axis 0.27 1.55 g

Output Change in Y-Axis −1.55 −0.27 g

Output Change in Z-Axis 0.40 1.95 g

POWER SUPPLY

Operating Voltage Range (VS) 1.7 2.6 2.75 V

Interface Voltage Range (VDD I/O) 1.7 1.8 VS V

Measurement Mode Supply Current ODR ≥ 100 Hz 140 μA

ODR < 10 Hz 30 μA

Standby Mode Supply Current 0.2 μA

Turn-On and Wake-Up Time9 ODR = 3200 Hz 1.4 ms

ADXL346 Data Sheet

Parameter Test Conditions Min1 Typ 2 Max1 Unit

TEMPERATURE

Operating Temperature Range −40 +85 °C

WEIGHT

Device Weight 18 mg

1 All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed.

2 The typical specifications shown are for at least 68% of the population of parts and are based on the worst case of mean ±1 σ except for 0 g output and sensitivity,

which represents the target value. For 0 g offset and sensitivity, the deviation from the ideal describes the worst case of mean ±1 σ.

3 Cross-axis sensitivity is defined as coupling between any two axes.

4 Bandwidth is the −3 dB frequency and is half the output data rate bandwidth = ODR/2.

5 The output format for the 3200 Hz and 1600 Hz ODRs is different from the output format for the remaining ODRs. This difference is described in the Data Formatting of

Upper Data Rates section.

6 Output data rates below 6.25 Hz exhibit additional offset shift with increased temperature, depending on selected output data rate. Refer to the Offset Performance at

Lowest Data Rates section for details.

7 These are typical values for the lowest and highest output data rate settings.

8 Self-test change is defined as the output (g) when the SELF_TEST bit = 1 (in the DATA_FORMAT register, Address 0x31) minus the output (g) when the SELF_TEST bit = 0.

Due to device filtering, the output reaches its final value after 4 × τ when enabling or disabling self-test, where τ = 1/(data rate). The part must be in normal power

operation (LOW_POWER bit = 0 in the BW_RATE register, Address 0x2C) for self-test to operate correctly.

9 Turn-on and wake-up times are determined by the user-defined bandwidth. At a 100 Hz data rate, the turn-on and wake-up times are each approximately 11.1 ms. For

other data rates, the turn-on and wake-up times are each approximately τ + 1.1 in milliseconds, where τ = 1/(data rate).

Rev. C | Page 4 of 40

Data Sheet ADXL346

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Acceleration

Any Axis, Unpowered

10,000 g

Any Axis, Powered 10,000 g

VS −0.3 V to +3.0 V

VDD I/O −0.3 V to +3.0 V

Digital Pins −0.3 V to VDD I/O + 0.3 V or

3.0 V, whichever is less

All Other Pins

−0.3 V to +3.0 V

Output Short-Circuit Duration

(Any Pin to Ground)

Indefinite

Temperature Range

Powered −40°C to +105°C

Storage −40°C to +105°C

Stresses at or above those listed under Absolute Maximum

Ratings may cause permanent damage to the product. This is a

stress rating only; functional operation of the product at these

or any other conditions above those indicated in the operational

section of this specification is not implied. Operation beyond

the maximum operating conditions for extended periods may

affect product reliability.

THERMAL RESISTANCE

Table 3. Package Characteristics

Package Type θJA θJC Device Weight

16-Terminal LGA 150°C/W 85°C/W 18 mg

PACKAGE INFORMATION

The information in Figure 2 and Table 4 provide details about

the package branding for ADXL346. For a complete listing of

product availability, see the Ordering Guide section.

Y2Z

vvvv

08167-047

Figure 2. Product Information on Package (Top View)

Table 4. Package Branding Information

Branding Key Field Description

Y2Z Part identifier for ADXL346

vvvv Factory lot code

ESD CAUTION

Rev. C | Page 5 of 40

ADXL346 Data Sheet

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

RESERVED

GND

SDO/

ALT ADDRESS

SDA/SDI/SDIO

NC = NO INTERNAL

CONNECTION

08167-002

DD I/O

SCL/SCLK

GND

INT1

INT2

TOP VIEW

ADXL346

(No t t o Scal e)

678

16 15 14

Figure 3. Pin Configuration (Top View)

Table 5. Pin Function Descriptions

Pin No. Mnemonic Description

1 VDD I/O Digital Interface Supply Voltage.

Not Internally Connected.

3 NC Not Internally Connected.

4 SCL/SCLK Serial Communications Clock.

5 NC Not Internally Connected.

6 SDA/SDI/SDIO Serial Data (I2C)/Serial Data Input (SPI 4-Wire)/Serial Data Input and Output (SPI 3-Wire).

SDO/ALT ADDRESS

Serial Data Output (SPI 4-Wire)/Alternate I2C Address Select (I2C).

8 CS Chip Select.

9 INT2 Interrupt 2 Output.

10 NC Not Internally Connected.

11 INT1 Interrupt 1 Output.

12 GND Must be connected to ground.

GND

Must be connected to ground.

14 VS

Supply Voltage.

15 RESERVED Reserved. This pin must be connected to VS.

16 GND Must be connected to ground.

Rev. C | Page 6 of 40

Data Sheet ADXL346

TYPICAL PERFORMANCE CHARACTERISTICS

–150 –100 –50 050 100 150

PERCENT OF POPULATION (%)

ZERO gOFFSET (mg)

08167-004

Figure 4. X-Axis Zero g Offset at 25°C, VS = 2.6 V

08167-005

–150 –100 –50 050 100 150

PERCENT OF POPULATION (%)

ZERO gOFFSET (mg)

Figure 5. Y-Axis Zero g Offset at 25°C, VS = 2.6 V

–150 –100 –50 050 100 150

PERCENT OF POPULATION (%)

ZERO gOFFSET (mg)

08167-006

Figure 6. Z-Axis Zero g Offset at 25°C, VS = 2.6 V

–150 –100 –50 050 100 150

PERCENT OF POPULATION (%)

ZERO gOFFSET (mg)

08167-104

Figure 7. X-Axis Zero g Offset at 25°C, VS = 1.8 V

08167-105

–150 –100 –50 050 100 150

PERCENT OF POPULATION (%)

ZERO gOFFSET (mg)

Figure 8. Y-Axis Zero g Offset at 25°C, VS = 1.8 V

–150 –100 –50 050 100 150

PERCENT OF POPULATION (%)

ZERO gOFFSET (mg)

08167-106

Figure 9. Z-Axis Zero g Offset at 25°C, VS = 1.8 V

Rev. C | Page 7 of 40

ADXL346 Data Sheet

–3 –2 –1 0 1

PERCENT OF POPULATION (%)

ZERO g O F F SET T EMPERATURE COEFFICIENT (mg/°C)

08167-010

Figure 10. X-Axis Zero g Offset Temperature Coefficient, VS = 2.6 V

08167-011

–3 –2 –1 0 1

PERCENT OF POPULATION (%)

ZERO g O F F SET T EMPERATURE COEFFICIENT (mg/°C)

Figure 11. Y-Axis Zero g Offset Temperature Coefficient, VS = 2.6 V

08167-012

–3 –2 –1 0 1

PERCENT OF POPULATION (%)

ZERO g O F F SET T EMPERATURE COEFFICIENT (mg/°C)

Figure 12. Z-Axis Zero g Offset Temperature Coefficient, VS = 2.6 V

–250

–200

–150

–100

–50

100

150

200

250

–40 –20 020 40 60 80 100

ZERO g OFFSET (mg)

TEMPERATURE (°C)

08167-013

Figure 13. X-Axis Zero g Offset vs. Temperature—

Eight Parts Soldered to PCB, VS = 2.6 V

–250

–200

–150

–100

–50

100

150

200

250

–40 –20 020 40 60 80 100

ZERO g OFFSET (mg)

TEMPERATURE (°C)

08167-014

Figure 14. Y-Axis Zero g Offset vs. Temperature—

Eight Parts Soldered to PCB, VS = 2.6 V

–250

–200

–150

–100

–50

100

150

200

250

–40 –20 020 40 60 80 100

ZERO g OFFSET (mg)

TEMPERATURE (°C)

08167-015

Figure 15. Z-Axis Zero g Offset vs. Temperature—

Eight Parts Soldered to PCB, VS = 2.6 V

Rev. C | Page 8 of 40

Data Sheet ADXL346

230 240 250 260 270 280

PERCENT OF POPULATION (%)

SENSITIVIT Y (L SB/g)

08167-016

Figure 16. X-Axis Sensitivity at 25°C, VS = 2.6 V, Full Resolution

08167-017

230 240 250 260 270 280

PERCENT OF POPULATION (%)

SENSITIVIT Y (L SB/g)

Figure 17. Y-Axis Sensitivity at 25°C, VS = 2.6 V, Full Resolution

08167-018

230 240 250 260 270 280

PERCENT OF POPULATION (%)

SENSITIVIT Y (L SB/g)

Figure 18. Z-Axis Sensitivity at 25°C, VS = 2.6 V, Full Resolution

230 240 250 260 270 280

PERCENT OF POPULATION (%)

SENSITIVIT Y (L SB/g)

08167-116

Figure 19. X-Axis Sensitivity at 25°C, VS = 1.8 V, Full Resolution

08167-117

230 240 250 260 270 280

PERCENT OF POPULATION (%)

SENSITIVIT Y (L SB/g)

Figure 20. Y-Axis Sensitivity at 25°C, VS = 1.8 V, Full Resolution

08167-118

230 240 250 260 270 280

PERCENT OF POPULATION (%)

SENSITIVIT Y (L SB/g)

Figure 21. Z-Axis Sensitivity at 25°C, VS = 1.8 V, Full Resolution

Rev. C | Page 9 of 40

ADXL346 Data Sheet

100

–0.10 –0.05 00.05 0.10

PERCENT OF POPULATION (%)

SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)

08167-022

Figure 22. X-Axis Sensitivity Temperature Coefficient, VS = 2.6 V

08167-023

100

–0.10 –0.05 00.05 0.10

PERCENT OF POPULATION (%)

SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)

Figure 23. Y-Axis Sensitivity Temperature Coefficient, VS = 2.6 V

08167-024

100

–0.10 –0.05 00.05 0.10

PERCENT OF POPULATION (%)

SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)

Figure 24. Z-Axis Sensitivity Temperature Coefficient, VS = 2.6 V

230

235

240

245

250

255

260

265

270

275

280

–40 –20 020 40 60 80 100

SENSITIVITY (LSB/g)

TEMPERATURE (°C)

08167-025

Figure 25. X-Axis Sensitivity vs. Temperature—

Eight Parts Soldered to PCB, VS = 2.6 V, Full Resolution

230

235

240

245

250

255

260

265

270

275

280

–40 –20 020 40 60 80 100

SENSITIVITY (LSB/g)

TEMPERATURE (°C)

08167-026

Figure 26. Y-Axis Sensitivity vs. Temperature—

Eight Parts Soldered to PCB, VS = 2.6 V, Full Resolution

230

235

240

245

250

255

260

265

270

275

280

–40 –20 020 40 60 80 100

SENSITIVITY (LSB/g)

TEMPERATURE (°C)

08167-127

Figure 27. Z-Axis Sensitivity vs. Temperature—

Eight Parts Soldered to PCB, VS = 2.6 V, Full Resolution

Rev. C | Page 10 of 40

Data Sheet ADXL346

0.5 0.6 0.7 0.8 0.9 1.0

SELF-TEST SHIFT (g)

PERCENT OF POPULATION (%)

08167-007

Figure 28. X-Axis Self-Test Response at 25°C, VS = 2.6 V

–1.0 –0.9 –0.8 –0.7 –0.6 –0.5

SELF-TEST SHIFT (g)

PERCENT OF POPULATION (%)

08167-008

Figure 29. Y-Axis Self-Test Response at 25°C, VS = 2.6 V

1.0 1.1 1.2 1.3 1.51.4

SELF-TEST SHIFT (g)

PERCENT OF POPULATION (%)

08167-009

Figure 30. Z-Axis Self-Test Response at 25°C, VS = 2.6 V

90 100 120 140 160 180110 130 150 170

OUT P UT CURRENT (µ A)

PERCENT OF POPULATION (%)

08167-019

Figure 31. Supply Current at 25°C, 100 Hz Output Data Rate, VS = 2.6 V

100

120

140

160

3.13 6.25 12.50 25 50 100 200 400 1600800 3200

SUPPLY CURRE NT (µ A)

OUT P UT DAT A RATE ( Hz )

08167-020

Figure 32. Supply Current vs. Output Data Rate at 25°C—10 Parts, VS = 2.6 V

100

110

120

130

140

150

1.6 1.8 2.0 2.2 2.4 2.6 2.8

SUPPLY CURRE NT CONS UM P TI ON (µ A)

SUPPLY VOLT AGE, V

(V)

08167-021

Figure 33. Supply Current vs. Supply Voltage at 25°C

Rev. C | Page 11 of 40

ADXL346 Data Sheet

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 with an

amplitude proportional to acceleration. Phase-sensitive de-

modulation 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 6. 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 (Bit D3) 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 6. Power Sequencing

Condition VS VDD I/O Description

Power Off Off Off The device is completely off, but there is a potential for a communication

bus conflict.

Bus Disabled On Off 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.

Bus Enabled Off On No functions are available, but the device will not create a conflict on the

communication bus.

Standby or

Measurement Mode

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.

Rev. C | Page 12 of 40

Data Sheet ADXL346

POWER SAVINGS

Power Modes

The ADXL346 automatically modulates its power consumption

in proportion to its output data rate, as outlined in Table 7. 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 D4) in the BW_RATE

mode is shown in Table 8 for cases where there is an advantage

to using low power mode. Use of low power mode for a data rate

not shown in Table 8 does not provide any advantage over the same

data rate in normal power mode. Therefore, it is recommended

that only data rates listed in Table 8 be used in low power mode.

The current consumption values shown in Table 7 and Table 8

are for a VS of 2.6 V.

Table 7. Typical Current Consumption vs. Data Rate

(TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Output Data

Rate (Hz) Bandwidth (Hz) Rate Code IDD (µA)

3200 1600 1111 140

1600

800

1110

800 400 1101 140

400 200 1100 140

200 100 1011 140

100 50 1010 140

50 25 1001 90

12.5

1000

12.5 6.25 0111 40

6.25 3.13 0110 31

3.13 1.56 0101 27

1.56 0.78 0100 23

0.78 0.39 0011 23

0.39 0.20 0010 23

0.20 0.10 0001 23

0.10 0.05 0000 23

Table 8. Typical Current Consumption vs. Data Rate, Low

Power Mode (TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Output Data

Rate (Hz) Bandwidth (Hz) Rate Code IDD (µA)

400 200 1100 90

200

100

1011

100 50 1010 40

50 25 1001 31

25 12.5 1000 27

12.5 6.25 0111 23

Autosleep Mode

Additional power can be saved if the ADXL346 automatically

switches to sleep mode during periods of inactivity. To enable

this feature, set the THRESH_INACT register (Address 0x25)

and the TIME_INACT register (Address 0x26) each to a value

that signifies inactivity (the appropriate value depends on the

application), and then set the AUTO_SLEEP bit (Bit D4) and the

link bit (Bit D5) in the POWER_CTL register (Address 0x2D).

Current consumption at the sub-8 Hz data rates used in this

mode is typically 23 µA for a VS of 2.6 V.

Standby Mode

For even lower power operation, standby mode can be used.

In standby mode, current consumption is reduced to 0.2 µA

(typical). In this mode, no measurements are made. Standby mode

is entered by clearing the measure bit (Bit D3) in the

POWER_CTL register (Address 0x2D). Placing the device into

standby mode preserves the contents of FIFO.

Rev. C | Page 13 of 40

ADXL346 Data Sheet

Rev. C | Page 14 of 40

SERIAL COMMUNICATIONS

I2C and SPI digital communications are available. In both cases,

the ADXL346 operates as a slave. I2C mode is enabled if the CS pin

is tied high to VDD I/O. The CS pin should always be tied high to

VDD I/O or be driven by an external controller because there is no

default mode if the CS pin is left unconnected. Therefore, not

taking these precautions may result in an inability to communicate

with the part. In SPI mode, the CS pin is controlled by the bus

master. In both SPI and I2C modes of operation, data transmitted

from the ADXL346 to the master device should be ignored during

writes to the ADXL346.

SPI

For SPI, either 3- or 4-wire configuration is possible, as shown in

the connection diagrams in Figure 34 and Figure 35. Clearing the

SPI bit (Bit D6) in the DATA_FORMAT register (Address 0x31)

selects 4-wire mode, whereas setting the SPI bit selects 3-wire

mode. The maximum SPI clock speed is 5 MHz with 100 pF

maximum loading, and the timing scheme follows clock polarity

(CPOL) = 1 and clock phase (CPHA) = 1. If power is applied to

the ADXL346 before the clock polarity and phase of the host

processor are configured, the CS pin should be brought high

before changing the clock polarity and phase. When using 3-wire

SPI, it is recommended that the SDO pin either be pulled up to

VDD I/O or be pulled down to GND via a 10 kΩ resistor.

PROCESSOR

D OUT

D IN/OUT

D OUT

ADXL346

SDIO

SDO

SCLK

08167-027

Figure 34. 3-Wire SPI Connection Diagram

PROCESSOR

D OUT

D IN

D OUT

ADXL346

SDI

SDO

SCLK

08167-028

Figure 35. 4-Wire SPI Connection Diagram

CS is the serial port enable line and is controlled by the SPI

master. This line must go low at the start of a transmission and

high at the end of a transmission, as shown in Figure 37. SCLK

is the serial port clock and is supplied by the SPI master. SCLK

should idle high during a period of no transmission. SDI and

SDO are the serial data input and output, respectively. Data is

updated on the falling edge of SCLK and should be sampled on

the rising edge of SCLK.

To read or write multiple bytes in a single transmission, the

multiple-byte bit, located after the R/W bit in the first byte transfer

(MB in Figure 37 to Figure 39), must be set. After the register

addressing and the first byte of data, each subsequent set of

clock pulses (eight clock pulses) causes the ADXL346 to point to

the next register for a read or write. This shifting continues until

the clock pulses cease and CS is deasserted. To perform reads or

writes on different, nonsequential registers, CS must be

deasserted between transmissions and the new register must be

addressed separately.

The timing diagram for 3-wire SPI reads or writes is shown in

Figure 39. The 4-wire equivalents for SPI writes and reads are

shown in Figure 37 and Figure 38, respectively. For correct

operation of the part, the logic thresholds and timing parameters

in Table 9 and Table 10 must be met at all times.

Use of the 3200 Hz and 1600 Hz output data rates is recom-

mended only with SPI communication rates greater than or

equal to 2 MHz. The 800 Hz output data rate is recommended

only for communication speeds greater than or equal to 400 kHz,

and the remaining data rates scale proportionally. For example,

the minimum recommended communication speed for a 200 Hz

output data rate is 100 kHz. Operation at an output data rate

above the recommended maximum may result in undesirable

effects on the acceleration data, including missing samples or

additional noise.

Preventing Bus Traffic Errors

The ADXL346 CS pin is used both for initiating SPI transactions,

and for enabling I2C mode. When the ADXL346 is used on a SPI

bus with multiple devices, its CS pin is held high while the master

communicates with the other devices. There may be conditions

where a SPI command transmitted to another device looks like

a valid I2C command. In this case, the ADXL346 would interpret

this as an attempt to communicate in I2C mode, and could inter-

fere with other bus traffic. Unless bus traffic can be adequately

controlled to assure such a condition never occurs, it is recom-

mended to add a logic gate in front of the SDI pin as shown in

Figure 36. This OR gate will hold the SDA line high when CS is

high to prevent SPI bus traffic at the ADXL346 from appearing

as an I2C start command.

PROCESSOR

D OUT

D IN

D OUT

ADXL346

SDI

SDO

SCLK

08167-236

Figure 36. Recommended SPI Connection Diagram when Using Multiple SPI

Devices on a Single Bus

Data Sheet ADXL346

Rev. C | Page 15 of 40

08167-129

DELAY

SETUP

HOLD

SDO

XXX

WMB A5 A0 D7 D0

XX X

ADDRESS BI T S DATA BITS

SCLK

QUIET

DIS

CS,DIS

SCLK

SDI

SDO

Figure 37. SPI 4-Wire Write

08167-130

XXX

RMBA5 A0

D7 D0X

ADDRESS BITS

DATA BITS

DIS

SCLK

SDI

SDO

QUIET

CS,DIS

SDO

SETUP

HOLD

DELAY

SCLK

Figure 38. SPI 4-Wire Read

08167-131

tDELAY

tSETUP tHOLD tSDO

R/W MB A5 A0 D7 D0

ADDRESS BITS DATA BIT S

tSCLK tMtStQUIET tCS,DIS

SCLK

SDIO

SDO

NOTES

tSDO

IS ONLY PRESENT DURING READS.

Figure 39. SPI 3-Wire Read/Write

ADXL346 Data Sheet

Rev. C | Page 16 of 40

Table 9. SPI Digital Input/Output

Limit1

Parameter Test Conditions Min Max Unit

Digital Input

Low Level Input Voltage (VIL) 0.3 × VDD I/O V

High Level Input Voltage (VIH) 0.7 × VDD I/O V

Low Level Input Current (IIL) VIN = VDD I/O 0.1 μA

High Level Input Current (IIH) VIN = 0 V −0.1 μA

Digital Output

Low Level Output Voltage (VOL) IOL = 10 mA 0.2 × VDD I/O V

High Level Output Voltage (VOH) IOH = −4 mA 0.8 × VDD I/O V

Low Level Output Current (IOL) VOL = VOL, max 10 mA

High Level Output Current (IOH) VOH = VOH, min −4 mA

Pin Capacitance fIN = 1 MHz, VIN = 2.6 V 8 pF

1 Limits are based on characterization results; not production tested.

Table 10. SPI Timing (TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)1

Limit2, 3

Parameter Min Max Unit Description

fSCLK 5 MHz SPI clock frequency

tSCLK 200 ns 1/(SPI clock frequency) mark-space ratio for the SCLK input is 40/60 to 60/40

tDELAY 5 ns CS falling edge to SCLK falling edge

tQUIET 5 ns SCLK rising edge to CS rising edge

tDIS 10 ns CS rising edge to SDO disabled

tCS,DIS 150 ns CS deassertion between SPI communications

tS 0.3 × tSCLK ns SCLK low pulse width (space)

tM 0.3 × tSCLK ns SCLK high pulse width (mark)

tSETUP 5 ns SDI valid before SCLK rising edge

tHOLD 5 ns SDI valid after SCLK rising edge

tSDO 40 ns SCLK falling edge to SDO/SDIO output transition

tR4 20 ns SDO/SDIO output low to output high transition

tF4 20 ns SDO/SDIO output high to output low transition

1 The CS, SCLK, SDI, and SDO pins are not internally pulled up or down; they must be driven for proper operation.

2 Limits are based on characterization results; not production tested.

3 The timing values are measured corresponding to the input thresholds (VIL and VIH) given in Table 9.

4 Output rise and fall times are measured with a capacitive load of 150 pF.

Data Sheet ADXL346

I2C

With CS tied high to VDD I/O, the ADXL346 is in I2C mode,

requiring a simple 2-wire connection as shown in Figure 40.

The ADXL346 conforms to the UM10204 I2C-Bus Specification

and User Manual, Rev. 03—19 June 2007, available from NXP

Semiconductors. It supports standard (100 kHz) and fast (400 kHz)

data transfer modes if the bus parameters given in Table 11 and

Table 12 are met. Single- or multiple-byte reads/writes are sup-

ported, as shown in Figure 41. With the ALT ADDRESS pin (Pin

7) high, the 7-bit I2C address for the device is 0x1D, followed by

the R/W bit. This translates to 0x3A for a write and 0x3B for a

read. An alternate I2C address of 0x53 (followed by the R/W bit)

can be chosen by grounding the ALT ADDRESS pin. This

translates to 0xA6 for a write and 0xA7 for a read.

There are no internal pull-up or pull-down resistors for any

unused pins; therefore, there is no known state or default state

for the CS or ALT ADDRESS pin if left floating or unconnected.

It is required that the CS pin be connected to VDD I/O and that

the ALT ADDRESS pin be connected to either VDD I/O or GND

when using I2C.

Due to communication speed limitations, the maximum output

data rate when using 400 kHz I2C is 800 Hz and scales linearly with

a change in the I2C communication speed. For example, using I2C

at 100 kHz would limit the maximum ODR to 200 Hz. Operation

at an output data rate above the recommended maximum may

result in an undesirable effect on the acceleration data, including

missing samples or additional noise.

PROCESSOR

D IN/OUT

D OUT

VDD I/O

ADXL346

SDA

ALT ADDRESS

SCL

08167-032

Figure 40. I2C Connection Diagram (Address 0x53)

If other devices are connected to the same I2C bus, the nominal

operating voltage level of these other devices cannot exceed VDD I/O

by more than 0.3 V. External pull-up resistors, RP, are necessary for

proper I2C operation. Refer to the UM10204 I2C-Bus Specification

and User Manual, Rev. 03—19 June 2007, when selecting pull-up

resistor values to ensure proper operation.

Table 11. I2C Digital Input/Output

Limit1

Parameter Test Conditions Min Max Unit

Digital Input

Low Level Input Voltage (V

)

0.3 × V

DD I/O

High Level Input Voltage (VIH) 0.7 × VDD I/O V

Low Level Input Current (IIL) VIN = VDD I/O 0.1 µA

High Level Input Current (IIH) VIN = 0 V −0.1 µA

Digital Output

Low Level Output Voltage (VOL) VDD I/O < 2 V, IOL = 3 mA 0.2 × VDD I/O V

VDD I/O ≥ 2 V, IOL = 3 mA 400 mV

Low Level Output Current (IOL) VOL = VOL, max 3 mA

Pin Capacitance fIN = 1 MHz, VIN = 2.6 V 8 pF

1 Limits are based on characterization results; not production tested.

08167-033

1THIS START IS EITHER A RESTART OR A STOP FOLLOWED BY A START.

NOTES

1. T HE S HADE D ARE AS RE P RE S E NT W HE N THE DEV ICE IS L IST E NING .

MASTER START SLAVE ADDRESS + WRIT E REGI ST ER ADDRESS

SLAVE ACK ACK ACK

MASTER START SLAVE ADDRESS + WRIT E REGI ST ER ADDRESS

SLAVE ACK ACK ACK ACK

MASTER START SLAVE ADDRESS + WRIT E REGI ST ER ADDRESS STOP

SLAVE ACK ACK

MASTER START

START1

SLAVE ADDRESS + WRI T E REGI ST ER ADDRESS NACK STOP

SLAVE ACK ACK DATA

STOP

ACK

SING L E- BYTE W RITE

MULTIPLE- BYTE WRI TE

DATA

MULTIPLE-BYTE READ

SLAVE ADDRESS + READ

ACK

DATA

STOP

NACK

ACK

SING L E- BYTE READ

Figure 41. I2C Device Addressing

Rev. C | Page 17 of 40

ADXL346 Data Sheet

Rev. C | Page 18 of 40

Table 12. I2C Timing (TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Limit1, 2

Parameter Min Max Unit Description

fSCL 400 kHz SCL clock frequency

t1 2.5 μs SCL cycle time

t2 0.6 μs tHIGH, SCL high time

t3 1.3 μs tLOW, SCL low time

t4 0.6 μs tHD, STA, start/repeated start condition hold time

t5 100 ns tSU, DAT, data setup time

t63, 4, 5, 6 0 0.9 μs tHD, DAT, data hold time

t7 0.6 μs tSU, STA, setup time for repeated start

t8 0.6 μs tSU, STO, stop condition setup time

t9 1.3 μs tBUF, bus-free time between a stop condition and a start condition

t10 300 ns tR, rise time of both SCL and SDA when receiving

0 ns tR, rise time of both SCL and SDA when receiving or transmitting

t11 300 ns tF, fall time of SDA when receiving

250 ns tF, fall time of both SCL and SDA when transmitting

CB 400 pF Capacitive load for each bus line

1 Limits are based on characterization results, with fSCL = 400 kHz and a 3 mA sink current; not production tested.

2 All values referred to the VIH and the VIL levels given in Table 11.

3 t6 is the data hold time that is measured from the falling edge of SCL. It applies to data in transmission and acknowledge.

4 A transmitting device must internally provide an output hold time of at least 300 ns for the SDA signal (with respect to VIH,min of the SCL signal) to bridge the undefined region of

the falling edge of SCL.

5 The maximum t6 value must be met only if the device does not stretch the low period (t3) of the SCL signal.

6 The maximum value for t6 is a function of the clock low time (t3), the clock rise time (t10), and the minimum data setup time (t5(min)). This value is calculated as t6(max) = t3 − t10 − t5(min).

SCL

START

CONDITION REPEATED

START

CONDITION

STOP

CONDITION

08167-034

Figure 42. I2C Timing Diagram

Data Sheet ADXL346

INTERRUPTS

The ADXL346 provides two output pins for driving interrupts:

INT1 and INT2. Both interrupt pins are push-pull, low impedance

pins with the output specifications listed in Table 13. The default

configuration of the interrupt pins is active high. This can be

changed to active low by setting the INT_INVERT bit (Bit D5)

in the DATA_FORMAT (Address 0x31) register. All functions

can be used simultaneously, with the only limiting feature being

that some functions may need to share interrupt pins.

Interrupts are enabled by setting the appropriate bit in the

INT_ENABLE register (Address 0x2E) and are mapped to either

the INT1 or INT2 pin based on the contents of the INT_MAP

pins, it is recommended that the functions and interrupt mapping

be done before enabling the interrupts. When changing the con-

figuration of an interrupt, it is recommended that the interrupt be

disabled first, by clearing the bit corresponding to that function in

the INT_ENABLE register, and then the function be reconfigured

before enabling the interrupt again. Configuration of the functions

while the interrupts are disabled helps to prevent the accidental

generation of an interrupt before it is desired.

The interrupt functions are latched and cleared by either reading

the DATAX, DATAY, and DATAZ registers (Address 0x32 to

Address 0x37) until the interrupt condition is no longer valid

for the data-related interrupts or by reading the INT_SOURCE

describes the interrupts that can be set in the INT_ENABLE

DATA_READY Bit

The DATA_READY bit is set when new data is available and is

cleared when no new data is available.

SINGLE_TAP Bit

The SINGLE_TAP bit is set when a single acceleration event

that is greater than the value in the THRESH_TAP register

(Address 0x1D) occurs for less time than is specified in

the DUR register (Address 0x21).

DOUBLE_TAP Bit

The DOUBLE_TAP bit is set when two acceleration events

that are greater than the value in the THRESH_TAP register

(Address 0x1D) occur for less time than is specified in the DUR

specified by the latent register (Address 0x22) but within the

time specified in the window register (Address 0x23). See the Tap

Detection section for more details.

Activity Bit

The activity bit is set when acceleration greater than the value stored

in the THRESH_ACT register (Address 0x24) is experienced on

any participating axis, as set by the ACT_INACT_CTL register

(Address 0x27).

Inactivity Bit

The inactivity bit is set when acceleration of less than the

value stored in the THRESH_INACT register (Address 0x25) is

experienced for more time than is specified in the TIME_INACT

ACT_INACT_CTL register (Address 0x27). The maximum value

for TIME_INACT is 255 sec.

FREE_FALL Bit

The FREE_FALL bit is set when acceleration of less than the

value stored in the THRESH_FF register (Address 0x28) is

experienced for more time than is specified in the TIME_FF

interrupt differs from the inactivity interrupt as follows: all axes

always participate and are logically AND’ed, the timer period is

much smaller (1.28 sec maximum), and the mode of operation is

always dc-coupled.

Watermark Bit

The watermark bit is set when the number of samples in FIFO

equals the value stored in the samples bits (Register FIFO_CTL,

Address 0x38). The watermark bit is cleared automatically when

FIFO is read, and the content returns to a value below the value

stored in the samples bits.

Table 13. Interrupt Pin Digital Output

Limit1

Parameter Test Conditions Min Max Unit

Digital Output

Low Level Output Voltage (VOL) IOL = 300 µA 0.2 × VDD I/O V

High Level Output Voltage (VOH) IOH = −150 µA 0.8 × VDD I/O V

Low Level Output Current (IOL) VOL = VOL, max 300 µA

High Level Output Current (IOH) VOH = VOH, min −150 µA

Pin Capacitance fIN = 1 MHz, VIN = 2.6 V 8 pF

Rise/Fall Time

Rise Time (tR)2 CLOAD = 150 pF 210 ns

Fall Time (tF)3 CLOAD = 150 pF 150 ns

1 Limits are based on characterization results; not production tested.

2 Rise time is measured as the transition time from VOL, max to VOH, min of the interrupt pin.

3 Fall time is measured as the transition time from VOH, min to VOL, max of the interrupt pin.

Rev. C | Page 19 of 40

ADXL346 Data Sheet

Overrun Bit

The overrun bit is set when new data replaces unread data. The

precise operation of the overrun function depends on the FIFO

mode. In bypass mode, the overrun bit is set when new data

replaces unread data in the DATAX, DATAY, and DATAZ registers

(Address 0x32 to Address 0x37). In all other modes, the overrun

bit is set when FIFO is filled. The overrun bit is automatically

cleared when the contents of FIFO are read.

Orientation Bit

The orientation bit is set when the orientation of the accelerometer

changes from a valid orientation to a different valid orientation.

An interrupt is not generated, however, if the orientation of the

accelerometer changes from a valid orientation to an invalid

orientation, or from a valid orientation to an invalid orientation

and then back to the same valid orientation. An invalid orientation

is defined as an orientation within the dead zone, or the region of

hysteresis. This region helps to prevent rapid orientation change

due to noise when the accelerometer orientation is close to the

boundary between two valid orientations.

The orientations that are valid for the interrupt depend on which

mode, 2D or 3D, is linked to the orientation interrupt. The mode is

selected with the INT_3D bit (Bit D3) in the ORIENT_CONF

(Read/Write) section for more details on how to enable the

orientation interrupt.

FIFO

The ADXL346 contains technology for an embedded memory

management system with 32-level FIFO that can be used to

minimize host processor burden. This buffer has four modes:

bypass, FIFO, stream, and trigger (see Table 22). Each mode is

selected by the settings of the FIFO_MODE bits (Bits[D7:D6])

in the FIFO_CTL register (Address 0x38).

Bypass Mode

In bypass mode, FIFO is not operational and, therefore,

remains empty.

FIFO Mode

In FIFO mode, data from measurements of the x-, y-, and z-axes

are stored in FIFO. When the number of samples in FIFO

equals the level specified in the samples bits of the FIFO_CTL

continues accumulating samples until it is full (32 samples from

measurements of the x-, y-, and z-axes) and then stops collecting

data. After FIFO stops collecting data, the device continues to

operate; therefore, features such as tap detection can be used

after FIFO is full. The watermark interrupt continues to occur

until the number of samples in FIFO is less than the value

stored in the samples bits of the FIFO_CTL register.

Stream Mode

In stream mode, data from measurements of the x-, y-, and z-

axes are stored in FIFO. When the number of samples in FIFO

equals the level specified in the samples bits of the FIFO_CTL

continues accumulating samples and holds the latest 32 samples

from measurements of the x-, y-, and z-axes, discarding older

data as new data arrives. The watermark interrupt continues

occurring until the number of samples in FIFO is less than the

value stored in the samples bits of the FIFO_CTL register.

Trigger Mode

In trigger mode, FIFO accumulates samples, holding the latest

32 samples from measurements of the x-, y-, and z-axes. After

a trigger event occurs and an interrupt is sent to the INT1 or

INT2 pin (determined by the trigger bit in the FIFO_CTL register),

FIFO keeps the last n samples (where n is the value specified by

the samples bits in the FIFO_CTL register) and then operates in

FIFO mode, collecting new samples only when FIFO is not full.

A delay of at least 5 μs should be present between the trigger event

occurring and the start of reading data from the FIFO to allow

the FIFO to discard and retain the necessary samples. Additional

trigger events cannot be recognized until the trigger mode is

reset. To reset the trigger mode, set the device to bypass mode

and then set the device back to trigger mode. Note that the FIFO

data should be read first because placing the device into bypass

mode clears FIFO.

Retrieving Data from FIFO

The FIFO data is read through the DATAX, DATAY, and DATAZ

registers (Address 0x32 to Address 0x37). When the FIFO is in

FIFO, stream, or trigger mode, reads to the DATAX, DATAY,

and DATAZ registers read data stored in the FIFO. Each time

data is read from the FIFO, the oldest x-, y-, and z-axes data are

placed into the DATAX, DATAY, and DATAZ registers.

If a single-byte read operation is performed, the remaining bytes of

data for the current FIFO sample are lost. Therefore, all axes of

interest should be read in a burst (or multiple-byte) read operation.

To ensure that the FIFO has completely popped (that is, that new

data has completely moved into the DATAX, DATAY, and DATAZ

registers), there must be at least 5 μs between the end of reading

the data registers and the start of a new read of the FIFO or a

read of the FIFO_STATUS register (Address 0x39). The end of

reading a data register is signified by the transition of data from

For SPI operation at 1.6 MHz or less, the register addressing

portion of the transmission is a sufficient delay to ensure that

the FIFO has completely popped. For SPI operation greater than

1.6 MHz, it is necessary to deassert the CS pin to ensure a total

delay of 5 μs; otherwise, the delay will not be sufficient. The total

delay necessary for 5 MHz operation is at most 3.4 μs. This is

not a concern when using I2C mode because the communication

rate is low enough to ensure a sufficient delay between FIFO reads.

Rev. C | Page 20 of 40

Data Sheet ADXL346

Rev. C | Page 21 of 40

SELF-TEST

The ADXL346 incorporates a self-test feature that effectively

tests its mechanical and electronic systems simultaneously.

When the self-test function is enabled (via the SELF_TEST bit

(Bit D7 in the DATA_FORMAT register, Address 0x31), an

electrostatic force is exerted on the mechanical sensor. This

electrostatic force moves the mechanical sensing element in the

same manner as acceleration would, and it is additive to the

acceleration experienced by the device. This added electrostatic

force results in an output change in the x-, y-, and z-axes. Because

the electrostatic force is proportional to VS2, the output change

varies with VS. This effect is shown in Figure 43.

The scale factors listed in Table 14 can be used to adjust the

expected self-test output limits for different supply voltages, VS.

The self-test feature of the ADXL346 also exhibits a bimodal

behavior. However, the limits listed in Table 1 and Table 15 to

Table 18 are valid for both potential self-test values due to bi-

modality. Use of the self-test feature at data rates less than 100 Hz

or at 1600 Hz may yield values outside these limits. Therefore,

the part must be in normal power operation (LOW_POWER

bit = 0 in the BW_RATE register, Address 0x2C) and be placed

into a data rate of 100 Hz through 800 Hz or 3200 Hz for the

self-test function to operate correctly.

1.6 1.8 2.0 2.2 2.4 2.6 2.8

SUPPLY VOLT AGE, V

(V)

SELF-TEST SHIFT LIMITS (g)

X-AXIS SELF-TEST HIGH LIMIT

X-AXIS SELF-TEST LOW LIMIT

Y-AXIS SELF-TEST HIGH LIMIT

Y-AXIS SELF-TEST LOW LIMIT

Z-AXIS SELF-T EST HIGH LIMI T

Z-AXIS SELF-TEST LOW LIMIT

08167-136

–3

–2

–1

Figure 43. Self-Test Output Change Limits vs. Supply Voltage

Table 14. Self-Test Output Scale Factors for Different Supply

Voltages, VS

Supply Voltage, VS X-, Y-Axes Z-Axis

1.70 V 0.43 0.38

1.80 V 0.48 0.47

2.00 V 0.59 0.58

2.60 V 1.00 1.00

2.75 V 1.13 1.11

Table 15. Self-Test Output in LSB for ±2 g, 10-Bit or Full

Resolution (TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis Min Max Unit

X 70 400 LSB

Y −400 −70 LSB

Z 100 500 LSB

Table 16. Self-Test Output in LSB for ±4 g, 10-Bit Resolution

(TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis Min Max Unit

X 35 200 LSB

Y −200 −35 LSB

Z 50 250 LSB

Table 17. Self-Test Output in LSB for ±8 g, 10-Bit Resolution

(TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis Min Max Unit

X 17 100 LSB

Y −100 −17 LSB

Z 25 125 LSB

Table 18. Self-Test Output in LSB for ±16 g, 10-Bit Resolution

(TA = 25°C, VS = 2.6 V, VDD I/O = 1.8 V)

Axis Min Max Unit

X 8 50 LSB

Y −50 −8 LSB

Z 12 63 LSB

ADXL346 Data Sheet

Table 19. Register Map

Address

Hex Dec Name Type Reset Value Description

0x00 0 DEVID R 11100110 Device ID.

0x01 to 0x1C 1 to 28 Reserved Reserved. Do not access.

0x1D 29 THRESH_TAP R/W 00000000 Tap threshold.

0x1E 30 OFSX R/W 00000000 X-axis offset.

0x1F 31 OFSY R/W 00000000 Y-axis offset.

0x20 32 OFSZ R/W 00000000 Z-axis offset.

0x21 33 DUR R/W 00000000 Tap duration.

0x22 34 Latent R/W 00000000 Tap latency.

0x23

Window

R/W

00000000

Tap window.

0x24 36 THRESH_ACT R/W 00000000 Activity threshold.

0x25 37 THRESH_INACT R/W 00000000 Inactivity threshold.

0x26 38 TIME_INACT R/W 00000000 Inactivity time.

0x27 39 ACT_INACT_CTL R/W 00000000 Axis enable control for activity and inactivity detection.

0x28 40 THRESH_FF R/W 00000000 Free-fall threshold.

0x29 41 TIME_FF R/W 00000000 Free-fall time.

0x2A 42 TAP_AXES R/W 00000000 Axis control for single tap/double tap.

0x2B 43 ACT_TAP_STATUS R 00000000 Source of single tap/double tap.

0x2C 44 BW_RATE R/W 00001010 Data rate and power mode control.

0x2D 45 POWER_CTL R/W 00000000 Power-saving features control.

0x2E

INT_ENABLE

R/W

00000000

Interrupt enable control.

0x2F 47 INT_MAP R/W 00000000 Interrupt mapping control.

0x30 48 INT_SOURCE R 00000010 Source of interrupts.

0x31 49 DATA_FORMAT R/W 00000000 Data format control.

0x32 50 DATAX0 R 00000000 X-Axis Data 0.

0x33 51 DATAX1 R 00000000 X-Axis Data 1.

0x34 52 DATAY0 R 00000000 Y-Axis Data 0.

0x35 53 DATAY1 R 00000000 Y-Axis Data 1.

0x36 54 DATAZ0 R 00000000 Z-Axis Data 0.

0x37 55 DATAZ1 R 00000000 Z-Axis Data 1.

0x38 56 FIFO_CTL R/W 00000000 FIFO control.

0x39 57 FIFO_STATUS R 00000000 FIFO status.

0x3A 58 TAP_SIGN R 00000000 Sign and source for single tap/double tap.

0x3B 59 ORIENT_CONF R/W 00100101 Orientation configuration.

0x3C 60 Orient R 00000000 Orientation status.

Rev. C | Page 22 of 40

Data Sheet ADXL346

D7 D6 D5 D4 D3 D2 D1 D0

1 1 1 0 0 1 1 0

The DEVID register holds a fixed device ID code of 0xE6

(346 octal).

The THRESH_TAP register is eight bits and holds the threshold

value for tap interrupts. The data format is unsigned, so the

magnitude of the tap event is compared with the value in

THRESH_TAP for normal tap detection. For information on

improved tap detection, refer to the Improved Tap Detection

section. The scale factor is 62.5 mg/LSB (that is, 0xFF = +16 g).

A value of 0 may result in undesirable behavior if single-tap/

double-tap interrupts are enabled.

OFSY, OFSZ (Read/Write)

The OFSX, OFSY, and OFSZ registers are each eight bits and

offer user-set offset adjustments in twos complement format

with a scale factor of 15.6 mg/LSB (that is, 0x7F = 2 g). The

values stored in the offset registers are automatically added to

the acceleration data, and the resulting value is stored in the

output data registers. For additional information regarding

offset calibration and the use of the offset registers, refer to the

Offset Calibration section.

The DUR register is eight bits and contains an unsigned time

value representing the maximum time that an event must be

above the THRESH_TAP threshold to qualify as a tap event. For

information on improved tap detection, refer to the Improved Tap

Detection section. The scale factor is 625 µs/LSB. A value of 0

disables the single-tap/double-tap functions.

The latent register is eight bits and contains an unsigned time

value representing the wait time from the detection of a tap

event to the start of the time window (defined by the window

For information on improved tap detection, refer to the Improved

Tap Detection section. The scale factor is 1.25 ms/LSB. A value of 0

disables the double-tap function.

The window register is eight bits and contains an unsigned time

value representing the amount of time after the expiration of the

latency time (determined by the latent register) during which a

second valid tap can begin. For information on improved tap

detection, refer to the Improved Tap Detection section. The scale

factor is 1.25 ms/LSB. A value of 0 disables the double-tap

function.

The THRESH_ACT register is eight bits and holds the threshold

value for detecting activity. The data format is unsigned, so the

magnitude of the activity event is compared with the value in the

THRESH_ACT register. The scale factor is 62.5 mg/LSB. A value

of 0 may result in undesirable behavior if the activity interrupt

is enabled.

The THRESH_INACT register is eight bits and holds the threshold

value for detecting inactivity. The data format is unsigned, so the

magnitude of the inactivity event is compared with the value in

the THRESH_INACT register. The scale factor is 62.5 mg/LSB. A

value of 0 may result in undesirable behavior if the inactivity

interrupt is enabled.

The TIME_INACT register is eight bits and contains an unsigned

time value representing the amount of time that acceleration

must be less than the value in the THRESH_INACT register for

inactivity to be declared. The scale factor is 1 sec/LSB. Unlike

the other interrupt functions, which use unfiltered data (see the

Threshold section), the inactivity function uses filtered output

data. At least one output sample must be generated for the

inactivity interrupt to be triggered. This results in the function

appearing unresponsive if the TIME_INACT register is set to a

value less than the time constant of the output data rate. A value

of 0 results in an interrupt when the output data is less than the

value in the THRESH_INACT register.

D7 D6 D5 D4

ACT ac/dc ACT_X enable ACT_Y enable ACT_Z enable

INACT ac/dc INACT_X enable INACT_Y enable INACT_Z enable

ACT AC/DC and INACT AC/DC Bits

A setting of 0 selects dc-coupled operation, and a setting of 1

enables ac-coupled operation. In dc-coupled operation, the

current acceleration magnitude is compared directly with

THRESH_ACT and THRESH_INACT to determine whether

activity or inactivity is detected.

In ac-coupled operation for activity detection, the acceleration

value at the start of activity detection is taken as a reference

value. New samples of acceleration are then compared to this

reference value, and if the magnitude of the difference exceeds

the THRESH_ACT value, the device triggers an activity interrupt.

Similarly, in ac-coupled operation for inactivity detection, a

reference value is used for comparison and is updated whenever

the device exceeds the inactivity threshold. After the reference

value is selected, the device compares the magnitude of the

difference between the reference value and the current acceleration

with THRESH_INACT. If the difference is less than the value in

THRESH_INACT for the time in TIME_INACT, the device is

considered inactive and the inactivity interrupt is triggered.

Rev. C | Page 23 of 40

ADXL346 Data Sheet

ACT_x Enable Bits and INACT_x Enable Bits

A setting of 1 enables x-, y-, or z-axis participation in detecting

activity or inactivity. A setting of 0 excludes the selected axis from

participation. If all axes are excluded, the function is disabled.

For activity detection, all participating axes are logically OR’ed,

causing the activity function to trigger when any of the partici-

pating axes exceeds the threshold. For inactivity detection, all

participating axes are logically AND’ed, causing the inactivity

function to trigger only if all participating axes are below the

threshold for the specified period of time.

The THRESH_FF register is eight bits and holds the threshold

value, in unsigned format, for free-fall detection. The acceleration

on all axes is compared with the value in THRESH_FF to deter-

mine if a free-fall event occurred. The scale factor is 62.5 mg/LSB.

Note that a value of 0 mg may result in undesirable behavior if

the free-fall interrupt is enabled. Values between 300 mg and

600 mg (0x05 to 0x09) are recommended.

The TIME_FF register is eight bits and stores an unsigned time

value representing the minimum time that the value of all axes

must be less than THRESH_FF to generate a free-fall interrupt.

The scale factor is 5 ms/LSB. A value of 0 may result in undesirable

behavior if the free-fall interrupt is enabled. Values between 100 ms

and 350 ms (0x14 to 0x46) are recommended.

D7 D6 D5 D4 D3 D2 D1 D0

0 0 0 Improved

tap

Suppress TAP_X

enable

TAP_Y

enable

TAP_Z

enable

Improved Tap Bit

The improved tap bit is used to enable improved tap detection.

This mode of operation improves tap detection by performing

an ac-coupled differential comparison of the output acceleration

data. The improved tap detection is performed on the same output

data available in the DATAX, DATAY, and DATAZ registers. Due

to the dependency on the output data rate and the ac-coupled

differential measurement, the threshold and timing values for

single taps and double taps must be adjusted for improved tap

detection. For further explanation of improved tap detection, see

the Improved Tap Detection section. Improved tap is enabled

by setting the improved tap bit to a value of 1 and is disabled

by clearing the bit to a value of 0.

Suppress Bit

Setting the suppress bit suppresses double-tap detection if

acceleration greater than the value in THRESH_TAP is present

between taps. See the Tap Detection section for more details.

TAP_x Enable Bits

A setting of 1 in the TAP_X enable, TAP_Y enable, or TAP_Z

enable bit enables x-, y-, or z-axis participation in tap detection.

A setting of 0 excludes the selected axis from participation in

tap detection.

D7 D6 D5 D4 D3 D2 D1 D0

0 ACT_X

source

ACT_Y

source

ACT_Z

source

Asleep TAP_X

source

TAP_Y

source

TAP_Z

source

ACT_x Source and TAP_x Source Bits

These bits indicate the first axis involved in a tap or activity

event. A setting of 1 corresponds to involvement in the event,

and a setting of 0 corresponds to no involvement. When new

data is available, these bits are not cleared but are overwritten by

the new data. The ACT_TAP_STATUS register should be read

before clearing the interrupt. Disabling an axis from participation

clears the corresponding source bit when the next activity or

single-tap/double-tap event occurs.

Asleep Bit

A setting of 1 in the asleep bit indicates that the part is asleep,

and a setting of 0 indicates that the part is not asleep. This bit

toggles only if the device is configured for autosleep. See the

information on autosleep mode.

D7 D6 D5 D4 D3 D2 D1 D0

0 0 0 LOW_POWER Rate

LOW_POWER Bit

A setting of 0 in the LOW_POWER bit selects normal operation,

and a setting of 1 selects reduced power operation, which is

associated with somewhat higher noise (see the Power Modes

section for details).

Rate Bits

These bits select the device bandwidth and output data rate (see

Table 7 and Table 8 for details). The default value is 0x0A, which

translates to a 100 Hz output data rate. An output data rate should

be selected that is appropriate for the communication protocol and

frequency selected. Selecting too high of an output data rate with a

low communication speed results in samples being discarded.

0 0 Link AUTO_SLEEP Measure Sleep Wakeup

Link Bit

A setting of 1 in the link bit with both the activity and inactivity

functions enabled delays the start of the activity function until

inactivity is detected. After activity is detected, inactivity detection

begins, preventing the detection of activity. This bit serially links

the activity and inactivity functions. When this bit is set to 0,

the inactivity and activity functions are concurrent. Additional

information can be found in the Link Mode section.

Rev. C | Page 24 of 40

Data Sheet ADXL346

When clearing the link bit, it is recommended that the part be

placed into standby mode and then set back to measurement

mode with a subsequent write. This is done to ensure that the

device is properly biased if sleep mode is manually disabled;

otherwise, the first few samples of data after the link bit is cleared

may have additional noise, especially if the device was asleep

when the bit was cleared.

AUTO_SLEEP Bit

If the link bit is set, a setting of 1 in the AUTO_SLEEP bit enables

the autosleep functionality. In this mode, the ADXL346 auto-

matically switches to sleep mode if the inactivity function is

enabled and inactivity is detected (that is, when acceleration is

below the THRESH_INACT value for at least the time indicated

by TIME_INACT). If activity is also enabled, the ADXL346

automatically wakes up from sleep after detecting activity and

returns to operation at the output data rate set in the BW_RATE

switching to sleep mode. See the description of the sleep bit in this

section for more information on sleep mode.

If the link bit is not set, the AUTO_SLEEP feature is disabled,

and setting the AUTO_SLEEP bit does not have any impact on

device operation. Refer to the Link Bit section or the Link Mode

section for more information about using the link feature.

When clearing the AUTO_SLEEP bit, it is recommended that the

part be placed into standby mode and then set back to measure-

ment mode with a subsequent write. This is done to ensure that

the device is properly biased if sleep mode is manually disabled;

otherwise, the first few samples of data after the AUTO_SLEEP

bit is cleared may have additional noise, especially if the device

was asleep when the bit was cleared.

Measure Bit

A setting of 0 in the measure bit places the part into standby mode,

and a setting of 1 places the part into measurement mode. The

ADXL346 powers up in standby mode with minimum power

consumption.

Sleep Bit

A setting of 0 in the sleep bit puts the part into the normal mode

of operation, and a setting of 1 places the part into sleep mode.

Sleep mode suppresses DATA_READY, stops transmission of data

to FIFO, and switches the sampling rate to one specified by the

wakeup bits. In sleep mode, only the activity function can be used.

While the DATA_READY interrupt is suppressed, the output

data registers are still updated at the sampling rate set by the

wakeup bits.

When clearing the sleep bit, it is recommended that the part be

placed into standby mode and then set back to measurement

mode with a subsequent write. This is done to ensure that the

device is properly biased if sleep mode is manually disabled;

otherwise, the first few samples of data after the sleep bit is

cleared may have additional noise, especially if the device was

asleep when the bit was cleared.

Wakeup Bits

These bits control the frequency of readings in sleep mode as

described in Table 20.

Table 20. Frequency of Readings in Sleep Mode

Setting

D1 D0 Frequency (Hz)

0 0 8

0 1 4

1 0 2

1 1 1

D7 D6 D5 D4

DATA_READY SINGLE_TAP DOUBLE_TAP Activity

D3 D2 D1 D0

Inactivity FREE_FALL Watermark Overrun/

orientation

Setting bits in this register to a value of 1 enables their respective

functions to generate interrupts, whereas a value of 0 prevents

the functions from generating interrupts. The DATA_READY,

watermark, and overrun/orientation bits enable only the interrupt

output; the functions are always enabled. It is recommended that

interrupts be configured before enabling their outputs.

D7 D6 D5 D4

DATA_READY SINGLE_TAP DOUBLE_TAP Activity

D3 D2 D1 D0

Inactivity FREE_FALL Watermark Overrun/

orientation

Bits set to 0 in this register send their respective interrupts to the

INT1 pin, whereas bits set to 1 send their respective interrupts to

the INT2 pin. All selected interrupts for a given pin are OR’ed.

D7 D6 D5 D4

DATA_READY SINGLE_TAP DOUBLE_TAP Activity

D3 D2 D1 D0

Inactivity FREE_FALL Watermark Overrun/

orientation

Bits set to 1 in this register indicate that their respective functions

have triggered an event, whereas bits set to 0 indicate that the

corresponding events have not occurred. The DATA_READY,

watermark, and overrun/orientation bits are always set if the

corresponding events occur, regardless of the INT_ENABLE

DATAX, DATAY, and DATAZ registers. The DATA_READY and

watermark bits may require multiple reads, as indicated in the

FIFO mode descriptions in the FIFO section. Other bits, and the

corresponding interrupts, including orientation if enabled, are

cleared by reading the INT_SOURCE register.

Rev. C | Page 25 of 40

ADXL346 Data Sheet

D7 D6 D5 D4 D3 D2 D1 D0

SELF_TEST SPI INT_INVERT 0 FULL_RES Justify Range

The DATA_FORMAT register controls the presentation of data

to Register 0x32 through Register 0x37. All data, except that for

the ±16 g range, must be clipped to avoid rollover.

SELF_TEST Bit

A setting of 1 in the SELF_TEST bit applies a self-test force to

the sensor, causing a shift in the output data. A value of 0 disables

the self-test force.

SPI Bit

A value of 1 in the SPI bit sets the device to 3-wire SPI mode,

and a value of 0 sets the device to 4-wire SPI mode.

INT_INVERT Bit

A value of 0 in the INT_INVERT bit sets the interrupts to active

high, and a value of 1 sets the interrupts to active low.

FULL_RES Bit

When this bit is set to a value of 1, the device is in full resolution

mode, where the output resolution increases with the g range

set by the range bits to maintain a 4 mg/LSB scale factor. When

the FULL_RES bit is set to 0, the device is in 10-bit mode, and

the range bits determine the maximum g range and scale factor.

Justify Bit

A setting of 1 in the justify bit selects left-justified (MSB) mode,

and a setting of 0 selects right-justified mode with sign extension.

Range Bits

These bits set the g range as described in Table 21.

Table 21. g Range Setting

Setting

D1 D0 g Range

0 0 ±2 g

0 1 ±4 g

±8

1 1 ±16 g

DATAY0, DATAY1, DATAZ0, DATAZ1 (Read Only)

These six bytes (Register 0x32 to Register 0x37) are eight bits

each and hold the output data for each axis. Register 0x32 and

and Register 0x37 hold the output data for the z-axis. The output

data is twos complement, with DATAx0 as the least significant byte

and DATAx1 as the most significant byte, where x represents X,

Y, or Z. The DATA_FORMAT register (Address 0x31) controls

the format of the data. It is recommended that a multiple-byte

read of all registers be performed to prevent a change in data

between reads of sequential registers.

D7 D6 D5 D4 D3 D2 D1 D0

FIFO_MODE Trigger Samples

FIFO_MODE Bits

These bits set the FIFO mode, as described in Table 22.

Table 22. FIFO Modes

Setting

D7 D6 Mode Function

0 0 Bypass FIFO is bypassed.

0 1 FIFO FIFO collects up to 32 values and then

stops collecting data, collecting new

data only when FIFO is not full.

1 0 Stream FIFO holds the last 32 data values.

When FIFO is full, the oldest data is

overwritten with newer data.

1 1 Trigger When triggered by the trigger bit,

FIFO holds the last data samples

before the trigger event and then

continues to collect data until FIFO is

full. New data is collected only when

FIFO is not full.

Trigger Bit

A value of 0 in the trigger bit links the trigger event of trigger mode

to INT1, and a value of 1 links the trigger event to INT2.

Samples Bits

The function of these bits depends on the FIFO mode selected (see

Table 23). Entering a value of 0 in the samples bits immediately

sets the watermark bit in the INT_SOURCE register (Address

0x30), regardless of which FIFO mode is selected. Undesirable

operation may occur if a value of 0 is used for the samples bits

when trigger mode is used.

Table 23. Samples Bits Functions

FIFO Mode Samples Bits Function

Bypass None.

FIFO Specifies how many FIFO entries are needed to

trigger a watermark interrupt.

Stream Specifies how many FIFO entries are needed to

trigger a watermark interrupt.

Trigger Specifies how many FIFO samples are retained in

the FIFO buffer before a trigger event.

Rev. C | Page 26 of 40

Data Sheet ADXL346

D7 D6 D5 D4 D3 D2 D1 D0

FIFO_TRIG 0 Entries

FIFO_TRIG Bit

A 1 in the FIFO_TRIG bit corresponds to a trigger event occurring,

and a 0 means that a FIFO trigger event has not occurred.

Entries Bits

These bits report how many data values are stored in FIFO.

Access to collect the data from FIFO is provided through the

DATAX, DATAY, and DATAZ registers. FIFO reads must be

done in burst or multiple-byte mode because each FIFO level is

cleared after any read (single- or multiple-byte) of FIFO. FIFO

stores a maximum of 32 entries, which equates to a maximum

of 33 entries available at any given time because an additional

entry is available at the output filter of the device.

D7 D6 D5 D4 D3 D2 D1 D0

0 XSIGN YSIGN ZSIGN 0 XTAP YTAP ZTAP

xSIGN Bits

These bits indicate the sign of the first axis involved in a tap

event. A setting of 1 corresponds to acceleration in the negative

direction, and a setting of 0 corresponds to acceleration in the

positive direction. These bits update only when a new single-

tap/double-tap event is detected, and only the axes enabled in the

TAP_AXES register (Address 0x2A) are updated. The TAP_SIGN

Sign section for more details.

xTAP Bits

These bits indicate the first axis involved in a tap event. A

setting of 1 corresponds to involvement in the event, and a

setting of 0 corresponds to no involvement. When new data is

available, these bits are not cleared but are overwritten by the

new data. The TAP_SIGN register should be read before clearing

the interrupt. Disabling an axis from participation clears the

corresponding source bit when the next single-tap/double-tap

event occurs.

D7 D6 D5 D4 D3 D2 D1 D0

INT_

ORIENT

Dead zone INT_

Divisor

INT_ORIENT Bit

Setting the INT_ORIENT bit enables the orientation interrupt.

A value of 1 overrides the overrun function of the device and

replaces overrun in the INT_MAP (Address 0x2F), INT_ENABLE

(Address 0x2E), and INT_SOURCE (Address 0x30) registers with

the orientation function. After setting the INT_ORIENT bit, the

orientation bits in the INT_MAP and INT_ENABLE registers must

be configured to map the orientation interrupt to INT1 or INT2

and to enable generation of the interrupt to the pin.

An orientation interrupt is generated whenever the orientation

status for the mode selected by the INT_3D bit changes in the

orient register (Address 0x3C). The orientation interrupt is

cleared by reading the INT_SOURCE register. Clearing the

INT_ORIENT bit, or the orientation bit in the INT_ENABLE

Writing to the BW_RATE register (Address 0x2C) or placing

the part into standby mode resets the orientation feature, clearing

the orientation filter and the interrupt. However, resetting the

orientation feature also resets the orientation status in the orient

generated when the next output sample is available if the present

orientation is not the default orientation. A value of 0 for the

INT_ORIENT bit disables generation of the orientation interrupt

and permits the use of the overrun function.

Dead Zone Bits

These bits determine the region between two adjacent orientations,

where the orientation is considered invalid and is not updated. A

value of 0 may result in undesirable behavior when the orientation

is close to the bisector between two adjacent regions. The dead zone

angle is determined by these bits, as described in Table 24. See the

Orientation Sensing section for more details.

Table 24. Dead Zone and Divisor Codes

Decimal Binary

Dead Zone Angle

(Degrees)

Divisor

Bandwidth (Hz)

0 000 5.1 ODR/9

1 001 10.2 ODR/22

010

15.2

ODR/50

3 011 20.4 ODR/100

4 100 25.5 ODR/200

5 101 30.8 ODR/400

6 110 36.1 ODR/800

7 111 41.4 ODR/1600

INT_3D Bit

If the orientation interrupt is enabled, the INT_3D bit determines

whether 2D or 3D orientation detection generates an interrupt.

A value of 0 generates an interrupt only if the 2D orientation

changes from a valid 2D orientation to a different valid 2D

orientation. A value of 1 generates an interrupt only if the 3D

orientation changes from a valid 3D orientation to a different

valid 3D orientation.

Divisor Bits

These bits set the bandwidth of the filter used to low-pass filter the

measured acceleration for stable orientation sensing. The divisor

bandwidth is determined by these bits, as detailed in Table 24,

where ODR is the output data rate set in the BW_RATE register

(Address 0x2C). See the Orientation Sensing section for more

details.

Rev. C | Page 27 of 40

ADXL346 Data Sheet

D7 D6 D5 D4 D3 D2 D1 D0

0 V2 2D_ORIENT V3 3D_ORIENT

Vx Bits

These bits show the validity of the 2D (V2) and 3D (V3) orienta-

tions. A value of 1 corresponds to the orientation being valid. A

value of 0 means that the orientation is invalid because the current

orientation is in the dead zone.

xD_ORIENT Bits

These bits represent the current 2D (2D_ORIENT) and 3D

(3D_ORIENT) orientations of the accelerometer. If the orien-

tation interrupt is enabled, this register is read to determine the

orientation of the device when the interrupt occurs. Because this

should be read at the time of the orientation interrupt to ensure

that the orientation change that caused the interrupt has been

identified. Orientation values are shown in Table 25 and Table 26.

See the Orientation Sensing section for more details.

Writing to the BW_RATE register (Address 0x2C) or placing

the part into standby mode resets the orientation feature, clearing

the orientation filter and the orientation status. An orientation

interrupt (if enabled) results from these actions if the orientation

during the next output sample is different from the default

value (+X for 2D orientation detection and undefined for 3D

orientation).

Table 25. 2D Orientation Codes

Decimal Binary Orientation Dominant Axis

0 00 Portrait positive +X

1 01 Portrait negative −X

2 10 Landscape positive +Y

3 11 Landscape negative −Y

Table 26. 3D Orientation Codes

Decimal Binary Orientation Dominant Axis

011

Front

4 100 Back −X

2 010 Left +Y

5 101 Right −Y

001

Top

6 110 Bottom −Z

Rev. C | Page 28 of 40

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 CS

SCL/SCLK

SDO/AL T ADDRESS

SDA/SDI/SDIO 3-W IRE OR

4-WIRE SPI

OR I2C

INTERFACE

VDD I/O

CI/O

INTERRUPT

CONTROL

08167-035

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

08167-036

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

TAP S (DUR)

LATENCY

TIME

(LATENT)

TIME WINDOW FOR

SECO ND TAP ( WI NDOW)

SECO ND TAP

SINGLE-TAP

INTERRUPT DOUBLE-TAP

INTERRUPT

THRESHOLD

(THRESH_TAP)

HI BW

INTERRUPTS

08167-037

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

ADXL346 Data Sheet

INVALI DATES DOUBL E TAP I F

SUPRESS BIT IS SET

TIME WINDOW FOR SECOND

TAP (WINDO W)

LATENCY

TIME (LATENT)

TIME LIMIT

FOR TAPS

(DUR)

HI BW

08167-038

Figure 47. Double-Tap Event Invalid Due to High g Event

When the Suppress Bit Is Set

A double-tap event can also be invalidated if acceleration above

the threshold is detected at the start of the time window for the

second tap (set by the window register (Address 0x23)). This results

in an invalid double tap at the start of this window, as shown in

Figure 48. Additionally, a double-tap event can be invalidated if

an acceleration exceeds the time limit for taps (set by the DUR

the end of the DUR time limit for the second tap event, also

shown in Figure 48.

INVALI DATES DOUBLE TAP

AT START OF WINDOW

TIME WINDOW FOR

SECO ND TAP ( WI NDOW)

LATENCY

TIME

(LATENT)

INVALIDATES

DOUBLE T AP AT

END OF DUR

TIME LIMIT

FOR TAPS

(DUR)

TIME LIMIT

FOR TAPS

(DUR)

TIME LIMIT

FOR TAPS

(DUR)

HI BW

08167-039

Figure 48. Tap Interrupt Function with Invalid Double Taps

Single taps, double taps, or both can be detected by setting the

respective bits in the INT_ENABLE register (Address 0x2E).

Control over participation of each of the three axes in single-tap/

double-tap detection is exerted by setting the appropriate bits in

the TAP_AXES register (Address 0x2A). For the double-tap

function to operate, both the latent and window registers must

be set to a nonzero value.

Every mechanical system has somewhat different single-tap/

double-tap responses based on the mechanical characteristics of

the system. Therefore, some experimentation with values for the

DUR, latent, window, and THRESH_TAP registers is required.

In general, a good starting point is to set the DUR register to a

value greater than 0x10 (10 ms), the latent register to a value greater

than 0x10 (20 ms), the window register to a value greater than

0x40 (80 ms), and the THRESH_TAP register to a value greater

than 0x30 (3 g). Setting a very low value in the latent, window, or

THRESH_TAP register may result in an unpredictable response

due to the accelerometer picking up echoes of the tap inputs.

After a tap interrupt has been received, the first axis to exceed

the THRESH_TAP level is reported in the ACT_TAP_STATUS

overwritten with new data.

IMPROVED TAP DETECTION

Improved tap detection is enabled by setting the improved tap

bit of the TAP_AXES register (Address 0x2A). When improved

tap detection is enabled, the filtered output data corresponding to

the output data rate set in the BW_RATE register (Address 0x2C)

is processed to determine if a tap event occurred. In addition, an

ac-coupled differential measurement is used. This results in the

timing values and threshold values for improved tap detection

being different from those used for normal tap detection.

When improved tap detection is used, new values must be

determined based on test results. In general, no timing values

(in the DUR, latent, or window registers) should be set that are

less than the time step resolution set by the output data rate.

The threshold value for improved tap detection can typically be

set much lower than the threshold for normal tap detection.

The value used depends on the value in the BW_RATE register

and should be determined through system testing. Refer to the

Threshold section for more details.

TAP SIGN

A negative sign is produced by experiencing a negative accel-

eration, which corresponds to tapping on the positive face of the

device for the desired axis. The positive face of the device is the

face such that movement in that direction is positive acceleration.

For example, tapping on the face that corresponds to the +X

direction, labeled as front in Figure 49, results in a negative sign

for the x-axis. Tapping on the face labeled as left in Figure 49

results in a negative sign for the y-axis, and tapping on the face

labeled top results in a negative sign for the z-axis. Conversely,

tapping on the back, right, or bottom side results in positive

signs for the corresponding axes.

FRONT

(+X)

LEFT

(+Y)

TOP

(+Z)

08167-046

Figure 49. 3D Orientation with Coordinate System

Rev. C | Page 30 of 40

Data Sheet ADXL346

THRESHOLD

The lower output data rates are achieved by decimating a

common sampling frequency inside the device. The activity,

free-fall, and single-tap/double-tap detection functions without

improved tap enabled are performed using undecimated data.

As the bandwidth of the output data varies with the data rate

and is lower than the bandwidth of the undecimated data, the

high frequency and high g data that is used to determine activity,

free-fall, and single-tap/double-tap events may not be present if

the output of the accelerometer is examined. This may result in

functions triggering when acceleration data does not appear to

meet the conditions set by the user for the corresponding function.

LINK MODE

The function of the link bit is to reduce the number of activity

interrupts that the processor must service by setting the device

to look for activity only after inactivity. For proper operation of

this feature, the processor must still respond to the activity and

inactivity interrupts by reading the INT_SOURCE register

(Address 0x30) and, therefore, clearing the interrupts. If an activity

interrupt is not cleared, the part cannot go into autosleep mode.

The asleep bit in the ACT_TAP_STATUS register (Address 0x2B)

indicates whether the part is asleep.

SLEEP MODE VS. LOW POWER MODE

In applications where a low data rate and low power consumption

are desired (at the expense of noise performance), it is recom-

mended that low power mode be used. The use of low power

mode preserves the functionality of the DATA_READY interrupt

and the FIFO for postprocessing of the acceleration data. Sleep

mode, while offering a low data rate and power consumption, is

not intended for data acquisition.

However, when sleep mode is used in conjunction with the

AUTO_SLEEP mode and the link mode, the part can automatically

switch to a low power, low sampling rate mode when inactivity

is detected. To prevent the generation of redundant inactivity

interrupts, the inactivity interrupt is automatically disabled

and activity is enabled. When the ADXL346 is in sleep mode, the

host processor can also be placed into sleep mode or low power

mode to save significant system power. Once activity is detected,

the accelerometer automatically switches back to the original

data rate of the application and provides an activity interrupt

that can be used to wake up the host processor. Similar to when

inactivity occurs, detection of activity events is disabled and

inactivity is enabled.

OFFSET CALIBRATION

Accelerometers are mechanical structures containing elements

that are free to move. These moving parts can be very sensitive

to mechanical stresses, much more so than solid-state electronics.

The 0 g bias or offset is an important accelerometer metric because

it defines the baseline for measuring acceleration. Additional

stresses can be applied during assembly of a system containing

an accelerometer. These stresses can come from, but are not

limited to, component soldering, board stress during mounting,

and application of any compounds on or over the component. If

calibration is deemed necessary, it is recommended that calibration

be performed after system assembly to compensate for these effects.

A simple method of calibration is to measure the offset while

assuming that the sensitivity of the ADXL346 is as specified in

Table 1. The offset can then be automatically accounted for by

using the built-in offset registers (Register 0x1E, Register 0x1F, and

DATAY, and DATAZ registers (Address 0x32 to Address 0x37)

already compensating for any offset.

In a no-turn or single-point calibration scheme, the part is oriented

such that one axis, typically the z-axis, is in the 1 g field of gravity

and the remaining axes, typically the x- and y-axes, are in a 0 g

field. The output is then measured by taking the average of a

series of samples. The number of samples averaged is a choice of

the system designer, but a recommended starting point is 0.1 sec

worth of data for data rates of 100 Hz or greater. This corresponds

to 10 samples at the 100 Hz data rate. For data rates of less than

100 Hz, it is recommended that at least 10 samples be averaged

together. These values are stored as X0g, Y0g, and Z+1g for the 0 g

measurements on the x- and y-axes and the 1 g measurement

on the z-axis, respectively.

The values measured for X0g and Y0g correspond to the offset of

the x- and y-axes, and compensation is done by subtracting those

values from the output of the accelerometer to obtain the actual

acceleration:

XACTUAL = XMEAS − X0g

YACTUAL = YMEAS − Y0g

Because the z-axis measurement is done in a 1 g field, a no-turn or

single-point calibration scheme assumes an ideal sensitivity, SZ,

for the z-axis. This is subtracted from Z+1g to attain the z-axis

offset, which is then subtracted from future measured values to

obtain the actual value:

Z0g = Z1g − SZ

ZACTUAL = ZMEAS − Z0g

The ADXL346 can automatically compensate the output for offset

by using the offset registers (Register 0x1E, Register 0x1F, and

value that is automatically added to all measured acceleration

values, and the result is then placed into the DATAX, DATAY,

and DATAZ registers. Because the value placed in an offset register

is additive, a negative value is placed into the register to eliminate a

positive offset and vice versa for a negative offset. The register

has a scale factor of 15.6 mg/LSB and is independent of the

selected g range.

As an example, assume that the ADXL346 is placed into full-

resolution mode with a sensitivity of typically 256 LSB/g. The

part is oriented such that the z-axis is in the field of gravity and

the outputs of the x-, y-, and z-axes are measured as +10 LSB,

−13 LSB, and +9 LSB, respectively. Using the previous equations,

X0g is +10 LSB, Y0g is −13 LSB, and Z0g is +9 LSB. Each LSB of

Rev. C | Page 31 of 40

ADXL346 Data Sheet

output in full-resolution is 3.9 mg or one-quarter of an LSB of

the offset register.

Because the offset register is additive, the 0 g values are negated

and rounded to the nearest LSB of the offset register:

XOFFSET = −Round(10/4) = −3 LSB

YOFFSET = −Round(−13/4) = 3 LSB

ZOFFSET = −Round(9/4) = −2 LSB

These values are programmed into the OFSX, OFSY, and OFXZ

registers, respectively, as 0xFD, 0x03, and 0xFE. As with all

registers in the ADXL346, the offset registers do not retain the

value written into them when power is removed from the part.

Power-cycling the ADXL346 returns the offset registers to their

default value of 0x00.

Because the no-turn or single-point calibration method assumes an

ideal sensitivity in the z-axis, any error in the sensitivity results in

offset error. For instance, if the actual sensitivity was 250 LSB/g

in the previous example, the offset would be 15 LSB, not 9 LSB.

To help minimize this error, an additional measurement point

can be used with the z-axis in a 0 g field, and the 0 g measurement

can be used in the ZACTUAL equation.

USING SELF-TEST

The self-test change is defined as the difference between the

acceleration output of an axis with self-test enabled and the

acceleration output of the same axis with self-test disabled (see

Endnote 8 of Table 1). This definition assumes that the sensor

does not move between these two measurements, because if the

sensor moves, a non–self-test related shift corrupts the test.

Proper configuration of the ADXL346 is also necessary for an

accurate self-test measurement. The part should be set with a data

rate of 100 Hz through 800 Hz, or 3200 Hz. This is done by

ensuring that a value of 0x0A through 0x0D, or 0x0F is written

into the rate bits (Bit D3 through Bit D0) in the BW_RATE

normal power operation by ensuring that the LOW_POWER

bit (Bit D4) in the BW_RATE register is cleared

(LOW_POWER bit = 0) for accurate self-test measurements. It

is recommended that the part be set to full-resolution, 16 g

mode to ensure that there is sufficient dynamic range for the

entire self-test shift. This is done by setting the FULL_RES bit

(Bit D3) and writing a value of 0x03 to the range bits (Bit D1

and Bit D0) of the DATA_FORMAT register (Address 0x31).

This results in a high dynamic range for measurement and a

3.9 mg/LSB scale factor.

After the part is configured for accurate self-test measurement,

several samples of acceleration data for the x-, y-, and z-axes

should be retrieved from the sensor and averaged together. The

number of samples averaged is a choice of the system designer,

but a recommended starting point is 0.1 sec worth of data for

data rates of 100 Hz or greater. This corresponds to 10 samples

at the 100 Hz data rate. For data rates of less than 100 Hz, it is

recommended that at least 10 samples be averaged together. The

averaged values should be stored and labeled appropriately as the

self-test disabled data, that is, XST_OFF, YST_OFF, and ZST_OFF.

Next, self-test should be enabled by setting Bit D7 of the

DATA_FORMAT register (Address 0x31). The output needs some

time (about four samples) to settle once self-test is enabled. After

allowing the output to settle, several samples of acceleration data

for the x-, y-, and z-axes should be taken again and averaged. It

is recommended that the same number of samples be taken for

this average as was previously taken. These averaged values should

again be stored and labeled appropriately as the value with self-

test enabled, that is, XST_ON, YST_ON, and ZST_ON. Self-test can then

be disabled by clearing Bit D7 of the DATA_FORMAT register

(Address 0x31).

With the stored values for self-test enabled and disabled, the

self-test change is as follows:

XST = XST_ON − XST_OFF

YST = YST_ON − YST_OFF

ZST = ZST_ON − ZST_OFF

Because the measured output for each axis is expressed in LSBs,

XST, YST, and ZST are also expressed in LSBs. These values can be

converted to g’s of acceleration by multiplying each value by the

3.9 mg/LSB scale factor, if configured for full-resolution mode.

Additionally, Table 15 through Table 18 correspond to the self-test

range converted to LSBs and can be compared with the measured

self-test change when operating at a VS of 2.6 V. For other voltages,

the minimum and maximum self-test output values should be

adjusted based on (multiplied by) the scale factors shown in

Table 14. If the part was placed into ±2 g, 10-bit or full-resolution

mode, the values listed in Table 15 should be used. Although

the fixed 10-bit mode or a range other than 16 g can be used, a

different set of values, as indicated in Table 16 through Table 18,

would need to be used. Using a range below 8 g may result in

insufficient dynamic range and should be considered when

selecting the range of operation for measuring self-test.

If the self-test change is within the valid range, the test is considered

successful. Generally, a part is considered to pass if the minimum

magnitude of change is achieved. However, a part that changes

by more than the maximum magnitude is not necessarily a failure.

Another effective method for using the self-test to verify accel-

erometer functionality is to toggle the self-test at a certain rate

and then perform an FFT on the output. The FFT should have a

corresponding tone at the frequency the self-test was toggled.

This methodology removes the dependency of the test on supply

voltage and on self-test magnitude, which can vary within a rather

wide range.

ORIENTATION SENSING

The orientation function of the ADXL346 reports both 2D

and 3D orientation concurrently through the orient register

(Address 0x3C). The V2 and V3 bits (Bit D6 and Bit D3 in the

orient register) report the validity of the 2D and 3D orientation

Rev. C | Page 32 of 40

Data Sheet ADXL346

codes. If V2 or V3 are set, their respective code is a valid

orientation. If V2 or V3 are cleared, the orientation of the

accelerometer is unknown, such as when the orientation is

within the dead zone between valid regions.

For 2D orientation sensing, the relation of the x- and y-axes to

gravity is used to determine the accelerometer orientation (see

Figure 50 and Table 25). Portrait positive corresponds to the x-axis

being most closely aligned to the gravity vector and directed

upwards, opposite the gravity vector. Portrait negative is the

opposite of portrait positive, with the x-axis pointing downwards

along the gravity vector. Landscape positive corresponds to the

y-axis being most closely aligned with the gravity vector and

directed upwards, away from the gravity vector. Landscape

negative is the orientation opposite landscape positive. The

dead zone regions are shown in the orientations for portrait

positive (+X) and portrait negative (−X) of Figure 50. These

regions also exist for landscape positive (+Y) and landscape

negative (−Y), as shown in Figure 50.

In 3D orientation, the z-axis is also included. If the accelerometer is

placed in a Cartesian coordinate system, as shown in Figure 49 of

the Tap Sign section, the top of the device corresponds to the

positive z-axis direction, the front of the device corresponds to

the positive x-axis direction, and the right side of the device

corresponds to the positive y-axis direction.

The states shown in Table 26 correspond to which side of the

accelerometer is directed upwards, opposite the gravity vector.

As shown in Figure 49, the accelerometer is oriented in the top

state. If the device is flipped over such that the top of the device

is facing down, toward gravity, the orientation is reported as the

bottom state. If the device is adjusted such that the positive x-axis

or positive y-axis direction is pointing upwards, away from the

gravity vector, the accelerometer reports the orientation as front

or left, respectively.

The algorithm to detect orientation change is performed after

filtering the output acceleration data to eliminate the effects of

high frequency motion. This is performed by using a low-pass

filter with a bandwidth set by the divisor bits (ORIENT_CONF

output data available in the output data registers (Address 0x32

to Address 0x37); therefore, the orient register (Address 0x3C)

is updated at the same rate as the data rate that is set in the

BW_RATE register (Address 0x2C). Because the output data

is used, the bandwidth of the orientation filter depends on the

value set in the BW_RATE register, and the divisor bandwidth

values in Table 24 are referenced to the selected output data rate.

To eliminate most human motion, such as walking or shaking, the

value in the divisor bits (Bits[D2:D0]) of the ORIENT_CONF

orientation bandwidth to 1 Hz or 2 Hz. For example, with an

output data rate of 100 Hz, a divisor selection of 3 (ODR/100)

results in a 1 Hz bandwidth for orientation detection. For best

results, it is recommended that an output data rate of ≥25 Hz in

normal power mode and ≥200 Hz in low power operation be used.

+Y +g

+g+g

PORTRAIT

POSITI VE (00) NEGATIV E ( 01)

LANDSCAPE

POSITI VE (10) NEGATI V E ( 11)

DEADZONES

08167-040

Figure 50. 2D Orientation with Corresponding Codes

The width of the dead zone region between two orientation

positions is determined by setting the value of the dead zone bits

(Bits[D6:D4]) in the ORIENT_CONF register (Address 0x3B).

The dead zone region size can be specified as per the values

shown in Table 24. The dead zone angle represents the total

angle where the orientation is considered invalid. Therefore, a

dead zone of 15.4° corresponds to 7.7° in either direction away

from the bisector of two bordering regions. An example with a

dead zone region of 15.4° is shown in Figure 51. It should be

noted that the values shown in Table 24 correspond to the

typical dead zone angle when the gravity vector is completely

contained in only two axes (xy, xz, or yz) and should be used

only as a starting point. If the device is oriented such that the

projection of gravity onto all three axes is nonzero, the effective

sensitivity is reduced, causing an increase in the dead zone angle.

Therefore, evaluation needs to be performed for specific appli-

cation uses to determine the optimal setting for the dead zone.

+Y +g

PORTRAIT

POSITIVE

LANDSCAPE

52.7°

45°

37.3°

POSITIVE

DEADZONE

08167-041

Figure 51. Orientation Showing a 15.4° Dead Zone Region

By setting the INT_ORIENT bit (Bit D7) of the ORIENT_CONF

device is placed into a new valid orientation. Only one mode of

orientation detection, 2D or 3D, can generate an interrupt at a

time. The orientation detection mode is selected by setting or

clearing the INT_3D bit (Bit D3) of the ORIENT_CONF register

(Address 0x3B). For more details, refer to the Register 0x3B—

ORIENT_CONF (Read/Write) section.

Rev. C | Page 33 of 40

ADXL346 Data Sheet

Writing to the BW_RATE register or placing the part into standby

mode resets the orientation feature, clearing the orientation filter

and the orientation status. These actions cause an orientation

interrupt (if enabled), however, if the orientation during the

next output sample is different from the default value (+X for

2D orientation detection and undefined for 3D orientation).

DATA FORMATTING OF UPPER DATA RATES

Formatting of output data at the 3200 Hz and 1600 Hz output

data rates changes depending on the mode of operation (full-

resolution or fixed 10-bit) and the selected output range.

When using the 3200 Hz or 1600 Hz output data rates in

full-resolution or ±2 g, 10-bit operation, the LSB of the output

data-word is always 0. When data is right justified, this corresponds

to Bit D0 of the DATAx0 register, as shown in Figure 52. When

data is left justified and the part is operating in ±2 g, 10-bit mode,

the LSB of the output data-word is Bit D6 of the DATAx0 register.

In full-resolution operation when data is left justified, the location

of the LSB changes according to the selected output range. For a

range of ±2 g, the LSB is Bit D6 of the DATAx0 register; for ±4 g,

Bit D5 of the DATAx0 register; for ±8 g, Bit D4 of the DATAx0

shown in Figure 53.

The use of 3200 Hz and 1600 Hz output data rates for fixed 10-bit

operation in the ±4 g, ±8 g, and ±16 g output ranges provides an

LSB that is valid and that changes according to the applied accel-

eration. Therefore, in these modes of operation, Bit D0 is not

always 0 when output data is right justified, and Bit D6 is not

always 0 when output data is left justified. Operation at any data

rate of 800 Hz or lower also provides a valid LSB in all ranges and

modes that change according to the applied acceleration.

0D1D2D3D4D5D6D7

D0D1D2D3D4D5D6D7

D0D1D2D3D4D5D6

D0D1D2D3D4D5D6D7

DATAx1 REGI S TER DATAx0 REGI S TER

OUT P UT DAT A- WORD FO R

±16g, FULL-RESOLUTION MODE. OUT P UT DAT A- WORD FO R THE ±2g,

FULL-RESOLUTION AND ALL 10-BIT MODES.

THE ± 4g AND ± 8g FULL-RESOLUTION MODES HAVE THE SAME LSB LOCATION AS THE±2g

AND ±16g FULL-RESOLUTION MODES, BUT THE MSB LOCATION CHANGES TO BIT D2 AND

BIT D3 OF THE DAT Ax1 RE GI S TER F OR ±4gAND ±8g, RESPECTIVELY.

08167-145

Figure 52. Data Formatting When Output Data Is Right Justified

D1D2D3

D4D5D6

D0D1D2D3

D4D5D6D7

D0D1D2

D3D4D5

D6D7

D0D1

D2D3D4

D5D6D7

DATAx1 REGI S TER DATAx0 REGI S TER

MSB FOR ALL MODES

OF OPERATION WHEN

LEFT JUSTIFIED.

LSB FOR ±2g, FULL-RESOLUTION

AND ALL 10- BIT M ODES.

LSB FOR ±4g, FULL-RESOLUTION MODE.

LSB FOR ±8g, FULL-RESOLUTION MODE.

LSB FO R ±16g, FULL-RESOLUTION MODE.

FO R 3200Hz AND 1600Hz OUT P UT DATA RATES , THE LSB IN THE S E M ODES IS ALWAY S 0.

ADDIT IO NALLY , ANY BITS TO THE RI GHT OF THE L S B ARE ALW AY S 0 WHEN T HE OUT P UT

DATA IS LEFT JUSTIFIED.

08167-146

Figure 53. Data Formatting When Output Data Is Left Justified

Rev. C | Page 34 of 40

Data Sheet ADXL346

NOISE PERFORMANCE

The specification of noise shown in Table 1 corresponds to the

typical noise performance of the ADXL346 in normal power

operation with an output data rate of 100 Hz (LOW_POWER

bit = 0, rate = 0x0A in the BW_RATE register, Address 0x2C).

For normal power operation at data rates below 100 Hz, the noise

of the ADXL346 is equivalent to the noise at 100 Hz ODR in

LSBs. For data rates greater than 100 Hz, the noise increases

approximately by a factor of √2 per doubling of the data rate.

For example, at 400 Hz ODR, the noise on the x- and y-axes is

typically less than 2 LSB rms, and the noise on the z-axis is

typically less than 3 LSB rms.

For low power operation (LOW_POWER bit = 1 in the BW_RATE

for all valid data rates shown in Table 8. This value is typically

less than 2.83 LSB rms for the x- and y-axes and typically less

than 4.25 LSB rms for the z-axis.

The trend of noise performance for both normal power and low

power modes of operation of the ADXL346 is shown in Figure 54.

Figure 55 shows the typical Allan deviation for the ADXL346.

The 1/f corner of the device, as shown in this figure, is very low,

allowing absolute resolution of approximately 100 µg (assuming

that there is sufficient integration time). The figure also shows

that the noise density is 420 µg/√Hz for the x- and y-axes and

530 µg/√Hz for the z-axis.

Figure 56 shows the typical noise performance trend of the

ADXL346 over supply voltage. The performance is normalized

to the tested and specified supply voltage, VS = 2.6 V. The x-axis

offers the best noise performance over supply voltage, increasing by

typically less than 25% from nominal at a supply voltage of 1.8 V.

The performance of the y- and z-axes is comparable, with both

axes increasing by typically less than 35% when operating with a

supply voltage of 1.8 V. It should be noted, as shown in Figure 54,

that the noise on the z-axis is typically higher than that on the

y-axis; therefore, although the noise on the z- and y-axes change

roughly the same in percentage over supply voltage, the magnitude

of change on the z-axis is greater than the magnitude of change

on the y-axis.

OUT P UT NO ISE (LS B rms)

OUTPUT DATA RAT E ( Hz )

X-AXIS, NORMAL POWER

X-AXIS, LOW POWER

Y-AXIS, NORMAL POWER

Y-AXIS, LOW POWER

Z-AXIS, NORMAL POW ER

Z-AXIS, LOW POWER

08167-147

3.13 6.25 12.50 25 50 100 200 400 1600800 3200

Figure 54. Noise vs. Output Data Rate for Normal and Low Power Modes,

Full Resolution (256 LSB/g)

0.01 0.1 110 100 1k 10k

100

10k

AV E RAGING PE RIOD, (s)

ALLAN DEVIATION (µg)

08167-148

X-AXIS

Y-AXIS

Z-AXIS

Figure 55. Allan Deviation

100

110

120

130

140

150

1.6 1.8 2.0 2.2 2.4 2.6 2.8

PERCENTAGE OF NORMALIZED NOISE (%)

SUPPLY VOLTAGE, V

(V)

X-AXIS

Y-AXIS

Z-AXIS

08167-149

Figure 56. Normalized Noise vs. Supply Voltage

Rev. C | Page 35 of 40

ADXL346 Data Sheet

OPERATION AT VOLTAGES OTHER THAN 2.6 V

The ADXL346 is tested and specified at a supply voltage of

VS = 2.6 V; however, it can be powered with a VS as high as 2.75 V

or as low as 1.7 V. Some performance parameters change as the

supply voltage changes, including the offset, sensitivity, noise,

self-test, and supply current.

Due to minuscule changes in the electrostatic forces as supply

voltage is varied, the offset and sensitivity change slightly. When

operating at a supply voltage of VS = 1.8 V, the offset of the x- and

y-axes is typically 25 mg higher than at VS = 2.6 V operation. The

z-axis is typically 20 mg lower when operating at a supply voltage

of 1.8 V than when operating at VS = 2.6 V. Sensitivity on the

x- and y-axes typically shifts from a nominal 256 LSB/g (full-

resolution or ±2 g, 10-bit operation) at VS = 2.6 V operation to

250 LSB/g when operating with a supply voltage of 1.8 V. The z-axis

sensitivity is unaffected by a change in supply voltage and is the

same at VS = 1.8 V operation as it is at VS = 2.6 V operation. Simple

linear interpolation can be used to determine typical shifts in

offset and sensitivity at other supply voltages.

Changes in noise performance, self-test response, and supply

current are discussed elsewhere throughout the data sheet. For

more information about noise performance, review the Noise

Performance section. The Self-Test section discusses both the

operation of self-test over voltage (a square relationship with the

supply voltage) and the conversion of the self-test response in

g’s to LSBs. Finally, Figure 33 shows the impact of supply voltage

on typical current consumption at a 100 Hz output data rate,

with all other output data rates following the same trend.

OFFSET PERFORMANCE AT LOWEST DATA RATES

The ADXL346 offers several output data rates and bandwidths

designed for a wide range of applications. However, at the lowest

data rates, described as those data rates below 6.25 Hz, the offset

performance over temperature can vary significantly from the

remaining data rates. Figure 57, Figure 58, and Figure 59 show

the typical offset performance of the ADXL346 over temperature

for data rates of 6.25 Hz and lower. All plots are normalized to

the offset at 100 Hz output data rate; therefore, a nonzero value

corresponds to additional offset shift due to the temperature for

that data rate.

When using the lowest data rates, it is recommended that the

operating temperature range of the device be limited to provide

minimal offset shift across the operating temperature range.

Due to variability between parts, it is also recommended that

calibration over temperature be performed if any data rates

below 6.25 Hz are in use.

100

120

140

25 35 45 55 65 75 85

NORMALIZED OUTPUT (LSB)

TEMPERATURE (°C)

0.10Hz

0.20Hz

0.39Hz

0.78Hz

1.56Hz

3.13Hz

6.25Hz

08167-056

Figure 57. Typical X-Axis Output vs. Temperature at Lower Data Rates,

Normalized to 100 Hz Output Data Rate, VS = 2.6 V

100

120

140

25 35 45 55 65 75 85

NORMALIZED OUTPUT (LSB)

TEMPERATURE (°C)

0.10Hz

0.20Hz

0.39Hz

0.78Hz

1.56Hz

3.13Hz

6.25Hz

08167-057

Figure 58. Typical Y-Axis Output vs. Temperature at Lower Data Rates,

Normalized to 100 Hz Output Data Rate, VS = 2.6 V

–20

100

120

140

25 35 45 55 65 75 85

NORMALIZED OUTPUT (LSB)

TEMPERATURE (°C)

0.10Hz

0.20Hz

0.39Hz

0.78Hz

1.56Hz

3.13Hz

6.25Hz

08167-058

Figure 59. Typical Z-Axis Output vs. Temperature at Lower Data Rates,

Normalized to 100 Hz Output Data Rate, VS = 2.6 V

Rev. C | Page 36 of 40

Data Sheet ADXL346

AXES OF ACCELERATION SENSITIVITY

08167-042

Figure 60. Axes of Acceleration Sensitivity (Corresponding Output Increases When Accelerated Along the Sensitive Axis)

08167-043

GRAVITY

OUT

= +1g

OUT

= 0g

OUT

= 0g

OUT

= –1g

OUT

= 0g

OUT

= 0g

TOP

OUT

= 0g

OUT

= +1g

OUT

= 0g

TOP

OUT

= 0g

OUT

= –1g

OUT

= 0g

TOP

OUT

= 0g

OUT

= 0g

OUT

= +1g

OUT

= 0g

OUT

= 0g

OUT

= –1g

TOP

Figure 61. Output Response vs. Orientation to Gravity

Rev. C | Page 37 of 40

ADXL346 Data Sheet

LAYOUT AND DESIGN RECOMMENDATIONS

Figure 62 shows the recommended printed wiring board land pattern. Figure 63 and Table 27 provide details about the recommended

soldering profile.

3.3500

0.8000

0.3000

0.5000

3.3500

08167-044

Figure 62. Recommended Printed Wiring Board Land Pattern

(Dimensions shown in millimeters)

t25°C TO P E AK

PREHEAT

CRITICAL ZONE

TL TO TP

TEMPERATURE

TIME

RAMP-DOWN

RAMP-UP

TSMIN

TSMAX

08167-045

Figure 63. Recommended Soldering Profile

Table 27. Recommended Soldering Profile1, 2

Condition

Profile Feature Sn63/Pb37 Pb-Free

Average Ramp Rate from Liquid Temperature (TL) to Peak Temperature (TP) 3°C/sec max 3°C/sec max

Preheat

Minimum Temperature (TSMIN) 100°C 150°C

Maximum Temperature (TSMAX) 150°C 200°C

Time from TSMIN to TSMAX (tS) 60 sec to 120 sec 60 sec to 180 sec

TSMAX to TL Ramp-Up Rate 3°C/sec max 3°C/sec max

Liquid Temperature (TL) 183°C 217°C

Time Maintained Above T

)

60 sec to 150 sec

Peak Temperature (TP) 240 + 0/−5°C 260 + 0/−5°C

Time of Actual TP − 5°C (tP) 10 sec to 30 sec 20 sec to 40 sec

Ramp-Down Rate 6°C/sec max 6°C/sec max

Time 25°C to Peak Temperature 6 minutes max 8 minutes max

1 Based on JEDEC Standard J-STD-020D.1.

2 For best results, the soldering profile should be in accordance with the recommendations of the manufacturer of the solder paste used.

Rev. C | Page 38 of 40

Data Sheet ADXL346

OUTLINE DIMENSIONS

07-30-2012-B

TOP VI EW BOTTOM VIEW

END VIEW

SEATING

PLANE

1.00

0.95

0.85

3.10

3.00 S Q

2.90

PI N 1

CORNER

0.79

0.74

0.69

0.50

0.275

0.10 0.350

0.250

13 1614

0.50

BSC

Figure 64. 16-Terminal Land Grid Array [LGA]

(CC-16-3)

Solder Terminations Finish Is Au over Ni

Dimensions shown in millimeters

ORDERING GUIDE

Model1

Measurement

Range (g)

Specified

Voltage (V)

Temperature

Range Package Description

Package

Option

Branding

Code

ADXL346ACCZ-R2 ±2, ±4, ±8, ±16 2.6 −40°C to +85°C 16-Terminal Land Grid Array [LGA] CC-16-3 Y2Z

ADXL346ACCZ-RL ±2, ±4, ±8, ±16 2.6 −40°C to +85°C 16-Terminal Land Grid Array [LGA] CC-16-3 Y2Z

ADXL346ACCZ-RL7 ±2, ±4, ±8, ±16 2.6 −40°C to +85°C 16-Terminal Land Grid Array [LGA] CC-16-3 Y2Z

EVAL-ADXL346Z Evaluation Board

EVAL-ADXL346Z-DB Inertial Sensor Development/Data Logger

Board

EVAL-ADXL346Z-M Analog Devices Inertial Sensor Evaluation

System, Includes ADXL346 Satellite

EVAL-ADXL346Z-S ADXL346 Satellite, Standalone

1 Z = RoHS Compliant Part.

Rev. C | Page 39 of 40

ADXL346 Data Sheet

NOTES

I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).

Analog Devices offers specific products designated for automotive applications; please consult your local Analog Devices sales representative for details. Standard products sold by

Analog Devices are not designed, intended, or approved for use in life support, implantable medical devices, transportation, nuclear, safety, or other equipment where malfunction

of the product can reasonably be expected to result in personal injury, death, severe property damage, or severe environmental harm. Buyer uses or sells standard products for use

in the above critical applications at Buyer's own risk and Buyer agrees to defend, indemnify, and hold harmless Analog Devices from any and all damages, claims, suits, or expenses

resulting from such unintended use.

registered trademarks are the property of their respective owners.

D08167-0-6/15(C)

Rev. C | Page 40 of 40

Mouser Electronics

Authorized Distributor

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ADXL346ACCZ-R2