ANALOG DEVICES ADXL345 Service Manual

Three-Axis, ±2/4/8/16g

Rev.

PrA

www.BDTIC.com/ADI

Preliminary Technical Data

FEATURES

Ultra low power: 25 to 130 µA at V
Power consumption scales automatically with bandwidth
User selectable fixed 10-bit resolution or 4mg/LSB scale

factor in all g-ranges, up to 13-bit resolution at ±16 g
32 level output data FIFO minimizes host processor load
Built in motion detection functions

• Tap/Double Tap detection

• Activity/Inactivity monitoring

• Free-Fall detection

Supply and I/O voltage range: 1.8 V to 3.6 V

2

SPI (3 and 4 wire) and I

C digital interfaces

Flexible interrupt modes – Any interrupt mappable to either

interrupt pin
Measurement ranges selectable via serial command
Bandwidth selectable via serial command
Wide temperature range (-40 to +85°C)
10,000 g shock survival
Pb free/RoHS compliant
Small and thin: 3 × 5 × 1 mm LGA package

APPLICATIONS

Handsets

aming and pointing devices

G
Personal navigation devices
HDD protection
Fitness equipment
Digital cameras

= 2.5 V (typ)

S

3 AXIS

3 AXIS

SENSOR

SENSOR

FUNCTIONAL BLOCK DIAGRAM

SENSE

SENSE

ELECTRONICS

ELECTRONICS

COM CS

COM CS

igure 1. ADXL345 Simplified Block Diagram

F

CONVERTER

CONVERTER

A/D

A/D

ADXL345

ADXL345

Digital Accelerometer

ADXL345

GENERAL DESCRIPTION

The ADXL345 is a small, thin, low power, three-axis
a

ccelerometer with high resolution (13-bit) measurement up to
±16 g. Digital output data is formatted as 16-bit twos
complement and is accessible through either a SPI (3- or 4­wire) or I

The ADXL345 is well suited for mobile device applications. It
measures the static acceleration of gravity in tilt-sensing
applications, as well as dynamic acceleration resulting from
motion or shock. Its high resolution (4mg/LSB) enables
resolution of inclination changes of as little as 0.25°.

Several special sensing functions are provided. Activity and
inactivity sensing detect the presence or lack of motion and if
the acceleration on any axis exceeds a user-set level. Tap sensing
detects single and double taps. Free-Fall sensing detects if the
device is falling. These functions can be mapped to interrupt
output pins. An integrated 32 level FIFO can be used to store
data to minimize host processor intervention.

Low power modes enable intelligent motion-based power
management with threshold sensing and active acceleration
measurement at extremely low power dissipation.

The ADXL345 is supplied in a small, thin 3 mm × 5 mm ×
1 mm, 14-lead, plastic package.

DIGITAL

DIGITAL

DIGITAL

FILTER

FILTER

FILTER

2

C digital interface.

VDDI/OVs

VDDI/OVs

POWER

POWER

POWER

MANAGEMENT

MANAGEMENT

MANAGEMENT

CONTROL

CONTROL

CONTROL

AND

AND

AND

INTERRUPT

INTERRUPT

INTERRUPT

LOGIC

LOGIC

LOGIC

SERIAL I/O

SERIAL I/OSERIAL I/O

INT1

INT1

INT2

INT2

SDA/SDI/SDIO

SDA/SDI/SDIO

SDO/ALT

SDO/ALT
ADDRESS

ADDRESS

SCL/SCLK

SCL/SCLK

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] ©2008 Analog Devices, Inc. All rights reserved.

ADXL345 Preliminary Technical Data

www.BDTIC.com/ADI

TABLE OF CONTENTS

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

I2C................................................................................................. 10

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

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

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

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

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

Absolute Maximum Ratings............................................................ 4

ESD Caution.................................................................................. 4

Pin Configuration and Descriptions.............................................. 5

Typical performance characteristics .............................................. 6

Functional Description.................................................................... 7

Device Operation ......................................................................... 7

Power Sequencing ........................................................................ 7

Power Saving ................................................................................. 7

Serial Communications ................................................................... 9

SPI................................................................................................... 9

Interrupts..................................................................................... 11

FIFO ............................................................................................. 11

Self Test ........................................................................................ 12

Register Map ................................................................................... 13

Register Definitions ................................................................... 14

Application ...................................................................................... 18

Power Supply Decoupling ......................................................... 18

Mechanical Considerations for Mounting.............................. 18

Tap Detection.............................................................................. 18

Threshold .................................................................................... 19

Link Mode ................................................................................... 19

Recommended PWB Land Pattern.......................................... 20

Recommended Soldering Profile ............................................. 21

Outline Dimensions....................................................................... 22

Ordering Guide .......................................................................... 22

REVISION HISTORY

11/08—Rev. PrA - Initial Version

Rev. PrA | Page 2 of 24

Preliminary Technical Data ADXL345

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SPECIFICATIONS

TA = 25°C, VS = 2.5 V, V

Table 1. Specifications1

Parameter Conditions Min Typ Max 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 Sensitivity2 ±1 %

OUTPUT RESOLUTION Each axis

All g-ranges 10-bit mode 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 X
Scale Factor at X
Sensitivity at X
Scale Factor at X
Sensitivity at X
Scale Factor at X
Sensitivity at X
Scale Factor at X

OUT

OUT

OUT

OUT

, Y

OUT

, Y

OUT

, Y

OUT

, Y

OUT

Sensitivity Change due to Temperature ±0.02 %/°C

0 g BIAS LEVEL Each axis

0 g Output (X

OUT

, Y

OUT

0 g Offset vs. Temperature <±1 mg/°C

NOISE PERFORMANCE

Noise (x-, y-axes) Data Rate = 100 Hz, ±2 g 10-bit or Full-Res. <1 LSB RMS
Noise (z-axis) Data Rate = 100 Hz, ±2 g 10-bit or Full-Res. <1.5 LSB RMS

OUTPUT DATA RATE / BANDWIDTH User Selectable

Measurement Rate3 0.1 3200 Hz

SELF TEST

Output Change X +0.31 +1.02 g
Output Change Y -0.31 -1.02 g
Output Change Z +0.46 +1.64 g

POWER SUPPLY

Operating Voltage Range (VS) 2.0 2.5 3.6 V
Interface Voltage Range (V
Supply Current Data Rate > 100 Hz 130 150 µA
Supply Current Data Rate < 10 Hz 25 µA
Standby Mode Leakage Current 0.1 2 µA
Turn-On Time4 Data Rate = 3200 Hz 1.4 ms

TEMPERATURE

Operating Temperature Range −40 85 °C

WEIGHT

Device Weight 20 mgrams

1

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

2

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

3

Bandwidth is half the output data rate.

4

Turn-on and wake-up times are determined by the user defined bandwidth. At 100 Hz data rate the turn-on/wake-up time is approximately 11.1 ms. For additional

data rates the turn-on/wake-up time is approximately τ + 1.1 in milliseconds, where τ is 1/(Data Rate).

= 1.8 V, Acceleration = 0 g, unless otherwise noted.

DD I/O

, Z

OUT

, Y

OUT

, Y

OUT

, Y

OUT

, Y

VS = 2.5 V, ±2 g 10-bit or Full-Resolution 232 256 286 LSB/g

OUT

, Z

VS = 2.5 V, ±2 g 10-bit or Full-Resolution 3.5 3.9 4.3 mg/LSB

OUT

OUT

, Z

VS = 2.5 V, ±4 g 10-bit mode 116 128 143 LSB/g

OUT

, Z

VS = 2.5 V, ±4 g 10-bit mode 7.0 7.8 8.6 mg/LSB

OUT

OUT

, Z

VS = 2.5 V, ±8 g 10-bit mode 58 64 71 LSB/g

OUT

, Z

VS = 2.5 V, ±8 g 10-bit mode 14.0 15.6 17.2 mg/LSB

OUT

OUT

, Z

VS = 2.5 V, ±16 g 10-bit mode 29 32 36 LSB/g

OUT

, Z

VS = 2.5 V, ±16 g 10-bit mode 28.1 31.2 34.3 mg/LSB

OUT

OUT

, Z

) VS = 2.5 V, TA = 25°C -150 0 +150 mg

OUT

) 1.7 1.8 VS V

DD I/O

Rev. PrA | Page 3 of 24

ADXL345 Preliminary Technical Data

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ABSOLUTE MAXIMUM RATINGS

Table 2. Absolute Maximum Ratings

Parameter Rating

Acceleration (Any Axis, Unpowered) 10,000 g
Acceleration (Any Axis, Powered) 10,000 g
VS −0.3 V to 3.6 V
V

−0.3 V to 3.6

DD I/O

All Other Pins −0.3 V to 3.6
Output Short-Circuit Duration

(Any Pin to Ground)
Temperature Range (Powered) −40°C to +105°C
Temperature Range (Storage) −40°C to +105°C

Indefinite

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on

he human body and test equipment and can discharge without detection. Although this product features

t
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.

Rev. PrA | Page 4 of 24

Preliminary Technical Data ADXL345

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PIN CONFIGURATION AND DESCRIPTIONS

igure 2. Pin Configuration (Top View)

F

Table 3. Pin Descriptions

Pin No. Mnemonic Description

1 V
2 GND Must be connected to ground
3 Reserved Reserved, must be connected to VS or left open
4 GND Must be connected to ground
5 GND Must be connected to ground
6 VS Supply Voltage
7
8 INT1 Interrupt 1 Output
9 INT2 Interrupt 2 Output
10 GND Must be connected to ground
11 Reserved Reserved, must be connected to GND or left open
12 SDO/ALT ADDRESS Serial Data Out, Alternate I2C Address Select
13 SDA/SDI/SDIO Serial Data (I2C), Serial Data In (SPI 4-Wire), Serial Data In/Out (SPI 3-Wire)
14 SCL/SCLK Serial Communications Clock

Digital Interface Supply Voltage

DD I/O

CS

Chip Select

SDO/ALT ADDRESS

Rev. PrA | Page 5 of 24

ADXL345 Preliminary Technical Data

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TYPICAL PERFORMANCE CHARACTERISTICS

Rev. PrA | Page 6 of 24

Preliminary Technical Data ADXL345

DD I/O

Rate (Hz)

Bandwidth

(Hz)

3200

1600

1111

130

1600

800

1110

80

800

400

1101

130

400

200

1100

130

200

100

1011

130

100501010

130

50251001

80

25

12.5

1000

55

12.5

6.25

0111

37

6.25

3.125

0110

25

3.125

1.563

0101

25

1.563

0.782

0100

25

0.782

0.39

0011

25

0.39

0.195

0010

25

0.195

0.098

0001

25

Data Rate

Bandwidth

(Hz)

3200

1600

1111

130

1600

800

1110

80

800

400

1101

130

400

200

1100

80

200

100

1011

55

100501010

37

50251001

30

25

12.5

1000

25

12.5

6.25

0111

25

6.25

3.125

0110

25

3.125

1.563

0101

25

1.563

0.782

0100

25

0.782

0.39

0011

25

0.39

0.195

0010

25

0.195

0.098

0001

25

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FUNCTIONAL DESCRIPTION

DEVICE OPERATION

The ADXL345 is a complete three-axis acceleration
measurement system with a selectable measurement range of
either ±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 it 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 acceleration forces. 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 beam and unbalances the
differential capacitor, resulting in a sensor output whose
amplitude is proportional to acceleration. Phase-sensitive
demodulation is used to determine the magnitude and polarity
of the acceleration.

POWER SEQUENCING

Power may be applied to V
damaging the ADXL345. All possible power on states are
summarized in Table 4. The interface voltage level is set with
the interface supply voltage V
ensure that the ADXL345 does not create a conflict on the
communications bus. For single-supply operation, V
the same as the main supply, V
application, V
desired interface voltage. Once VS is applied, the device enters
standby state, where power consumption is minimized and the
device waits for V
measurement state (setting the MEASURE bit in the
POWER_CTL register). Clearing the MEASURE bit returns the
device to standby state.

Table 4. Power Sequencing

Condition

Power Off Off Off

Bus Enabled Off On

can differ from VS to accommodate the

DD I/O

DD I/O

VSV

or V

S

to be applied and a command to enter

Description

Completely off, potential for
communications bus conflict.
No functions available, but will not create
conflict on communications bus.

in any sequence without

DD I/O

, which must be present to

DD I/O

DD I/O

. Conversely, in a dual-supply

S

can be

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 to 400Hz data rate range
at the expense of slightly greater noise. To enter lower power
mode, set the LOW_POWER bit(D4) in the BW_RATE
register.

Table 5. Current Consumption versus Data Rate

Output Data

0.098 0.048 0000 25

The current consumption in Low Power Mode is shown in
Table 6. Cases where there is no advantage to using Low Power
Mode are shaded.

Table 6. Current Consumption versus Data Rate in Low
Power Mode

Output

Rate Code IDD (µA)

Rate Code IDD (µA)

At power up the device is in Standby mode

Standby or

Measurement

On On

awaiting a command to enter measurement
mode and all sensor functions are off. Once
instructed to enter Measurement mode, all
sensor functions are available.

POWER SAVING

Power Modes

The ADXL345 automatically modulates its power consumption
proportionally with its output data rate as shown in Table 5. If

Rev. PrA | Page 7 of 24

0.098 0.048 0000 25

ADXL345 Preliminary Technical Data

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Auto Sleep Mode

Additional power can be saved by having the ADXL345
automatically switch to sleep mode during periods of inactivity.
To enable this feature set the THRESH_INACT register to an
acceleration value that signifies no activity (this value will
depend on the application), set TIME_INACT to an
appropriate inactivity time period (again, this will depend on
the application), and set the AUTO_SLEEP bit and the LINK bit
in the POWER_CTL register. Current consumption at the sub­8Hz data rates used in this mode is typically 25 µA.

Standby Mode

For even lower power operation Standby Mode can be used. In

tandby Mode current consumption is reduced to 2µA (typical).

S
In this mode no measurements are made and communication
with the ADXL345 is limited to single-byte read or writes.
Standby Mode is entered by clearing the MEASURE bit (D3) in
the POWER_CTL register. Placing the device into Standby
Mode will preserve the contents of the FIFO.

Rev. PrA | Page 8 of 24