Datasheet

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3-Axis, ±2 g/±4 g/±8 g/±16 g

Digital Accelerometer

Data Sheet

ADXL345

FEATURES

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

0.1 µA in standby mode at V

= 2.5 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

Supply voltage range: 2.0 V to 3.6 V

I/O voltage range: 1.7 V to V

SPI (3- and 4-wire) and I

C 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 × 5 mm × 1 mm LGA package

APPLICATIONS

Handsets

Medical instrumentation

Gaming and pointing devices

Industrial instrumentation

Personal navigation devices

Hard disk drive (HDD) protection

GENERAL DESCRIPTION

The ADXL345 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 a SPI (3- or 4-wire) or I

C digital interface.

The

ADXL345 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 (3.9 mg/LSB) enables measurement

of inclination changes 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. These functions can

be mapped individually to either of two interrupt output pins.

An integrated memory management system with a 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 ADXL345 is supplied in a small, thin, 3 mm × 5 mm × 1 mm,

14-lead, plastic package.

FUNCTIONAL BLOCK DIAGRAM

3-AXIS

SENSOR

SENSE

ELECTRONICS

DIGITAL

FILTER

ADXL345

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

07925-001

Figure 1.

Rev. E

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Summary of content (40 pages)

PAGE 1
Data Sheet 3-Axis, ±2 g/±4 g/±8 g/±16 g Digital Accelerometer ADXL345 FEATURES GENERAL DESCRIPTION Ultralow power: as low as 23 µA in measurement mode and 0.1 µA in standby mode at VS = 2.
PAGE 2
ADXL345 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Self-Test ....................................................................................... 22 Applications ....................................................................................... 1 Register Map ................................................................................... 23 General Description .......................................
PAGE 3
Data Sheet ADXL345 REVISION HISTORY 6/15—Rev. D to Rev. E Changes to Features Section and General Description Section ........................................................................... 1 Change to Figure 36 ........................................................................15 Change to FIFO Section .................................................................21 2/13—Rev. C to Rev. D Changes to Figure 13, Figure 14, and Figure 15 ............................ 9 Change to Table 15 .........
PAGE 4
ADXL345 Data Sheet SPECIFICATIONS TA = 25°C, VS = 2.5 V, VDD I/O = 1.8 V, acceleration = 0 g, CS = 10 µF tantalum, CI/O = 0.1 µF, output data rate (ODR) = 800 Hz, unless otherwise noted. All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed. Table 1.
PAGE 5
Data Sheet Parameter TEMPERATURE Operating Temperature Range WEIGHT Device Weight ADXL345 Test Conditions Min Typ1 −40 30 1 Max Unit +85 °C mg 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.
PAGE 6
ADXL345 Data Sheet ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 2. All Other Pins Output Short-Circuit Duration (Any Pin to Ground) Temperature Range Powered Storage Rating Table 3. Package Characteristics 10,000 g 10,000 g −0.3 V to +3.9 V −0.3 V to +3.9 V −0.3 V to VDD I/O + 0.3 V or 3.9 V, whichever is less −0.3 V to +3.
PAGE 7
Data Sheet ADXL345 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS ADXL345 TOP VIEW (Not to Scale) SCL/SCLK VDD I/O 1 GND 2 RESERVED 3 14 13 SDA/SDI/SDIO 12 SDO/ALT ADDRESS 11 RESERVED 10 NC 9 INT2 8 INT1 +x 4 GND 5 VS 6 +y +z 7 CS NOTES 1. NC = NO INTERNAL CONNECTION. 07925-002 GND Figure 3. Pin Configuration (Top View) Table 5. Pin Function Descriptions Pin No.
PAGE 8
ADXL345 Data Sheet 20 20 18 18 16 16 PERCENT OF POPULATION (%) 14 12 10 8 6 4 2 12 10 8 6 4 –100 0 50 –50 ZERO g OFFSET (mg) 100 150 0 –150 20 20 18 18 16 14 12 10 8 6 4 14 12 10 8 6 4 100 150 0 –150 –100 –50 0 50 ZERO g OFFSET (mg) 100 150 07925-208 –50 0 50 ZERO g OFFSET (mg) 07925-205 –100 Figure 8. Y-Axis Zero g Offset at 25°C, VS = 3.
PAGE 9
ADXL345 150 25 100 20 50 0 10 –50 5 –100 0 –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 2.0 ZERO g OFFSET TEMPERATURE COEFFICIENT (mg/°C) –150 –60 100 20 50 OUTPUT (mg) 25 –50 5 –100 –1.0 –0.5 0 0.5 1.0 1.5 2.0 ZERO g OFFSET TEMPERATURE COEFFICIENT (mg/°C) 20 40 60 80 100 0 10 –150 –60 07925-211 PERCENT OF POPULATION (%) 150 –1.5 0 Figure 13. X-Axis Zero g Offset vs. Temperature— 45 Parts Soldered to PCB, VS = 2.5 V 30 0 –2.0 –20 TEMPERATURE (°C) Figure 10.
PAGE 10
ADXL345 Data Sheet 40 55 35 45 PERCENT OF POPULATION (%) 40 35 30 25 20 15 10 25 20 15 10 5 5 230 234 238 242 246 250 254 258 262 266 270 274 278 282 SENSITIVITY (LSB/g) 0 –0.02 07925-216 0 –0.01 0 0.01 0.02 SENSITIVITY TEMPERATURE COEFFICIENT (%/°C) Figure 19. X-Axis Sensitivity Temperature Coefficient, VS = 2.5 V Figure 16. X-Axis Sensitivity at 25°C, VS = 2.
PAGE 11
ADXL345 280 275 275 270 270 265 265 260 255 250 245 260 255 250 245 240 240 235 235 0 20 40 60 80 100 120 TEMPERATURE (°C) 230 –40 270 270 265 265 SENSITIVITY (LSB/g) 275 260 255 250 245 80 100 120 TEMPERATURE (°C) 230 –40 275 270 270 265 265 SENSITIVITY (LSB/g) 275 260 255 250 245 80 100 TEMPERATURE (°C) 60 80 100 120 245 235 60 40 250 240 40 20 255 235 20 0 260 240 120 07925-224 SENSITIVITY (LSB/g) 280 0 –20 Figure 26.
PAGE 12
ADXL345 Data Sheet 25 50 PERCENT OF POPULATION (%) PERCENT OF POPULATION (%) 60 40 30 20 20 15 10 5 0.2 0.5 0.8 1.1 1.4 1.7 2.0 SELF-TEST RESPONSE (g) 0 07925-228 0 100 110 120 130 140 150 160 170 180 190 200 CURRENT CONSUMPTION (µA) 07925-231 10 Figure 31. Current Consumption at 25°C, 100 Hz Output Data Rate, VS = 2.5 V Figure 28. X-Axis Self-Test Response at 25°C, VS = 2.5 V 160 60 CURRENT CONSUMPTION (µA) 40 30 20 10 100 80 60 40 –0.5 –0.8 –1.1 –1.4 –1.
PAGE 13
Data Sheet ADXL345 THEORY OF OPERATION The ADXL345 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, that 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.
PAGE 14
ADXL345 Data Sheet POWER SAVINGS Table 8. Typical Current Consumption vs. Data Rate, Low Power Mode (TA = 25°C, VS = 2.5 V, VDD I/O = 1.8 V) Power Modes The ADXL345 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.
PAGE 15
Data Sheet ADXL345 SERIAL COMMUNICATIONS I2C and SPI digital communications are available. In both cases, the ADXL345 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.
PAGE 16
ADXL345 Data Sheet CS tM tSCLK tDELAY tS tQUIET tCS,DIS SCLK tHOLD MB W SDI A5 tSDO X SDO A0 D7 ADDRESS BITS X D0 tDIS DATA BITS X X X X 07925-017 tSETUP Figure 37. SPI 4-Wire Write CS tM tSCLK tDELAY tS tCS,DIS tQUIET SCLK tHOLD R SDI MB tSDO X SDO A0 A5 X X tDIS ADDRESS BITS X X D7 X D0 07925-018 tSETUP DATA BITS Figure 38.
PAGE 17
Data Sheet ADXL345 Table 9. SPI Digital Input/Output Parameter Digital Input Low Level Input Voltage (VIL) High Level Input Voltage (VIH) Low Level Input Current (IIL) High Level Input Current (IIH) Digital Output Low Level Output Voltage (VOL) High Level Output Voltage (VOH) Low Level Output Current (IOL) High Level Output Current (IOH) Pin Capacitance 1 Test Conditions Min Limit1 Max 0.3 × VDD I/O 0.
PAGE 18
ADXL345 Data Sheet 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 maxi-mum may result in undesirable effect on the acceleration data, including missing samples or additional noise.
PAGE 19
Data Sheet ADXL345 Table 12. I2C Timing (TA = 25°C, VS = 2.5 V, VDD I/O = 1.8 V) Parameter fSCL t1 t2 t3 t4 t5 t63, 4, 5, 6 t7 t8 t9 t10 Limit1, 2 Max 400 Min 2.5 0.6 1.3 0.6 100 0 0.6 0.6 1.3 Unit kHz µs µs µs µs ns µs µs µs µs ns ns ns ns pF 0.
PAGE 20
ADXL345 Data Sheet INTERRUPTS DOUBLE_TAP The ADXL345 provides two output pins for driving interrupts: INT1 and INT2. Both interrupt pins are push-pull, low impedance pins with output specifications shown 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 in the DATA_FORMAT (Address 0x31) register.
PAGE 21
Data Sheet ADXL345 Overrun Trigger Mode 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.
PAGE 22
ADXL345 Data Sheet SELF-TEST Table 14. Self-Test Output Scale Factors for Different Supply Voltages, VS The ADXL345 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 in the DATA_FORMAT register, Address 0x31), an electrostatic force is exerted on the mechanical sensor.
PAGE 23
Data Sheet ADXL345 REGISTER MAP Table 19.
PAGE 24
ADXL345 Data Sheet Register 0x25—THRESH_INACT (Read/Write) REGISTER DEFINITIONS Register 0x00—DEVID (Read Only) D7 1 D6 1 D5 1 D4 0 D3 0 D2 1 D1 0 D0 1 The DEVID register holds a fixed device ID code of 0xE5 (345 octal). Register 0x1D—THRESH_TAP (Read/Write) The THRESH_TAP register is eight bits and holds the threshold value for tap interrupts. The data format is unsigned, therefore, the magnitude of the tap event is compared with the value in THRESH_TAP for normal tap detection.
PAGE 25
Data Sheet ADXL345 ACT_x Enable Bits and INACT_x Enable Bits Asleep Bit 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 participating axes exceeds the threshold.
PAGE 26
ADXL345 Data Sheet If the link bit is not set, the AUTO_SLEEP feature is disabled and setting the AUTO_SLEEP bit does not have an impact on device operation. Refer to the Link Bit section or the Link Mode section for more information on utilization of 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 measurement mode with a subsequent write.
PAGE 27
Data Sheet ADXL345 INT_INVERT Bit Table 22. FIFO Modes 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. Setting D7 D6 0 0 0 1 Mode Bypass FIFO 1 0 Stream 1 1 Trigger 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.
PAGE 28
ADXL345 Data Sheet APPLICATIONS INFORMATION POWER SUPPLY DECOUPLING TAP DETECTION 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 ADXL345 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.
PAGE 29
Data Sheet ADXL345 Several events can occur to invalidate the second tap of a double tap event. First, if the suppress bit in the TAP_AXES register (Address 0x2A) is set, any acceleration spike above the threshold during the latency time (set by the latent register) invalidates the double tap detection, as shown in Figure 47. TIME LIMIT FOR TAPS (DUR) LATENCY TIME (LATENT) TIME WINDOW FOR SECOND TAP (WINDOW) 07925-038 XHI BW INVALIDATES DOUBLE TAP IF SUPRESS BIT SET Figure 47.
PAGE 30
ADXL345 Data Sheet SLEEP MODE VS. LOW POWER MODE In applications where a low data rate and low power consumption is desired (at the expense of noise performance), it is recommended 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.
PAGE 31
Data Sheet ADXL345 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 4 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 ADXL345 is also necessary for an accurate self-test measurement.
PAGE 32
ADXL345 Data Sheet 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 register; and for ±16 g, Bit D3 of the DATAx0 register. This is shown in Figure 50. 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 (fullresolution or fixed 10-bit) and the selected output range.
PAGE 33
Data Sheet ADXL345 10k NOISE PERFORMANCE The trend of noise performance for both normal power and low power modes of operation of the ADXL345 is shown in Figure 51. Figure 52 shows the typical Allan deviation for the ADXL345. 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).
PAGE 34
ADXL345 Data Sheet 140 120 NORMALIZED OUTPUT (LSB) OFFSET PERFORMANCE AT LOWEST DATA RATES 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. 80 0.10Hz 0.20Hz 0.39Hz 0.78Hz 1.56Hz 3.13Hz 6.
PAGE 35
Data Sheet ADXL345 AXES OF ACCELERATION SENSITIVITY AZ AX 07925-021 AY Figure 57. Axes of Acceleration Sensitivity (Corresponding Output Voltage Increases When Accelerated Along the Sensitive Axis) XOUT = 1g YOUT = 0g ZOUT = 0g TOP TOP TOP GRAVITY XOUT = 0g YOUT = 1g ZOUT = 0g XOUT = –1g YOUT = 0g ZOUT = 0g XOUT = 0g YOUT = 0g ZOUT = 1g Figure 58. Output Response vs. Orientation to Gravity Rev.
PAGE 36
ADXL345 Data Sheet LAYOUT AND DESIGN RECOMMENDATIONS Figure 59 shows the recommended printed wiring board land pattern. Figure 60and Table 24 provide details about the recommended soldering profile. 3.3400 1.0500 0.5500 0.2500 3.0500 07925-014 5.3400 0.2500 1.1450 Figure 59. Recommended Printed Wiring Board Land Pattern (Dimensions shown in millimeters) CRITICAL ZONE TL TO TP tP TP tL TSMAX TSMIN tS RAMP-DOWN PREHEAT 07925-015 TEMPERATURE RAMP-UP TL t25°C TO PEAK TIME Figure 60.
PAGE 37
Data Sheet ADXL345 OUTLINE DIMENSIONS PAD A1 CORNER 3.00 BSC 0.49 BOTTOM VIEW 13 14 0.813 × 0.50 1 0.80 BSC 5.00 BSC 0.50 8 7 6 TOP VIEW END VIEW 0.79 0.74 0.69 1.01 0.49 1.50 03-16-2010-A PKG-003340 1.00 0.95 0.85 SEATING PLANE Figure 61.
PAGE 38
ADXL345 Data Sheet NOTES Rev.
PAGE 39
Data Sheet ADXL345 NOTES Rev.
PAGE 40
ADXL345 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.