Page 1
3-Axis, ±1.5 g/±3 g/±6 g/±12 g
VSV
FEATURES
Ultralow power: as low as 57 μA in measurement mode and
0.1 μA in standby mode at V
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 ±12 g (maintaining 2.9 mg/LSB
scale factor in all g ranges)
Embedded, patent pending FIFO technology minimizes host
processor load
Built-in motion detection functions for activity/inactivity
monitoring
Supply and I/O voltage range: 2.0 V to 3.6 V
SPI (3- and 4-wire) and I
Flexible interrupt modes mappable to either interrupt pin
Measurement ranges selectable via serial command
Bandwidth selectable via serial command
Wide temperature range (−40 to +105°C)
10,000 g shock survival
Pb free/RoHS compliant
Small and thin: 5 mm × 5 mm × 1.45 mm LFCSP package
Qualified for automotive applications
APPLICATIONS
Car alarm
Hill start aid (HSA)
Electronic parking brake
Data recorder (black box)
= 3.3 V (typical)
S
2
C digital interfaces
FUNCTIONAL BLOCK DIAGRAM
Digital Accelerometer
ADXL312
GENERAL DESCRIPTION
The ADXL312 is a small, thin, low power, 3-axis accelerometer
with high resolution (13-bit) measurement up to ±12 g. Digital
output data is formatted as 16-bit twos complement and is
accessible through either a SPI (3- or 4-wire) or I
interface.
The ADXL312 is well suited for car alarm or black box 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 (2.9 mg/LSB) enables
resolution of inclination changes of as little as 0.25°. A built-in
FIFO facilitates using oversampling techniques to improve
resolution to as little as 0.05° of inclination.
Several special sensing functions are provided. Activity and
inactivity sensing detects the presence or absence of motion and
whether the acceleration on any axis exceeds a user-set level.
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 ADXL312 is supplied in a small, thin 5 mm × 5 mm ×
1.45 mm, 32-lead, LFCSP package.
DD I/O
2
C digital
ADXL312
SENSE
3-AXIS
SENSOR
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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.
ELECTRONICS
GND
Figure 1. ADXL312 Simplified Block Diagram
ADC
DIGITAL
FILTER
32 LEVEL
FIFO
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2010 Analog Devices, Inc. All rights reserved.
POWER
MANAGEMENT
CONTROL
AND
INTERRUPT
LOGIC
SERIAL I/O
CS
INT1
INT2
SDA/SDI/SDIO
SDO/ALT
ADDRESS
SCL/SCLK
08791-001
Page 2
ADXL312
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
ESD Caution.................................................................................. 5
Pin Configuration and Function Descriptions............................. 6
Typical Performance Characteristics............................................. 7
Theory of Operation ......................................................................10
Power Sequencing ...................................................................... 10
Power Savings ............................................................................. 10
Serial Communications ................................................................. 12
SPI................................................................................................. 12
I2C................................................................................................. 15
Interrupts..................................................................................... 17
FIFO............................................................................................. 18
Self-Test ....................................................................................... 19
Register Map ................................................................................... 20
Register Definitions ................................................................... 21
Applications Information.............................................................. 25
Power Supply Decoupling......................................................... 25
Mechanical Considerations for Mounting.............................. 25
Threshold .................................................................................... 25
Link Mode................................................................................... 25
Sleep Mode vs. Low Power Mode............................................. 25
Using Self-Test ............................................................................26
Data Formatting of Upper Data Rates..................................... 27
Noise Performance .....................................................................28
Axes of Acceleration Sensitivity ...............................................29
Solder Profile................................................................................... 30
Outline Dimensions....................................................................... 31
Ordering Guide .......................................................................... 32
Automotive Products................................................................. 32
REVISION HISTORY
Revision 0: Initial Version
Rev. 0 | Page 2 of 32
Page 3
ADXL312
SPECIFICATIONS
TA = −40°C to +105°C, VS = V
Table 1. Specifications
1
Parameter Conditions Min Typ Max Unit
SENSOR INPUT Each axis
Measurement Range User selectable ±1.5, 3, 6, 12
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 Default resolution 10 Bits
±1.5 g Range Full resolution enabled 10 Bits
±3 g Range Full resolution enabled 11 Bits
±6 g Range Full resolution enabled 12 Bits
±12 g Range Full resolution enabled 13 Bits
SENSITIVITY Each axis
Scale Factor at X
Scale Factor at X
Scale Factor at X
Scale Factor at X
OUT
OUT
OUT
OUT
, Y
, Y
, Y
, Y
OUT
OUT
OUT
OUT
, Z
, Z
, Z
, Z
Sensitivity at X
Sensitivity at X
Sensitivity at X
Sensitivity at X
OUT
OUT
OUT
OUT
, Y
, Y
, Y
, Y
OUT
OUT
OUT
OUT
, Z
, Z
, Z
, Z
OUT
OUT
OUT
OUT
Sensitivity Change Due to Temperature ±0.01 %/°C
0 g BIAS LEVEL Each axis
Initial 0 g Output T = 25°C, X
Initial 0 g Output T = 25°C, Z
0 g Output over Temperature −40°C < T < 105°C, X
0 g Offset Tempco X
0 g Offset Tempco Z
NOISE PERFORMANCE
Noise Density (X-, Y-axes) 200 340 440 μg/√Hz
Noise Density (Z-axis) 200 470 595 μg/√Hz
OUTPUT DATA RATE/BANDWIDTH User selectable
Measurement Rate3 6.25 3200 Hz
SELF-TEST4 Data rate ≥ 100 Hz, 2.0 ≤ VS ≤ 3.6
Output Change in X-Axis 0.20 2.10
Output Change in Y-Axis −2.10 −0.20
Output Change in Z-Axis 0.30 3.40
POWER SUPPLY
Operating Voltage Range (VS) 2.0 3.6 V
Interface Voltage Range (V
Supply Current Data rate > 100 Hz 100 170 300 μA
Data rate < 10 Hz 30 55 110 μA
Standby Mode Leakage Current 0.1 2 μA
Turn-On (Wale-Up) Time5 1.4 ms
TEMPERATURE
Operating Temperature Range −40 +105 °C
= 3.3 V, acceleration = 0 g, unless otherwise noted.
DD I/O
g
±1.5 g, 10-bit or full resolution 2.6 2.9 3.2 mg/LSB
OUT
±3 g, 10-bit resolution 5.2 5.8 6.4 mg/LSB
OUT
±6 g, 10-bit resolution 10.4 11.6 12.8 mg/LSB
OUT
±12 g, 10-bit resolution 20.9 23.2 25.5 mg/LSB
OUT
±1.5 g, 10-bit or full resolution 312 345 385 LSB/g
±3 g, 10-bit resolution 156 172 192 LSB/g
±6 g, 10-bit resolution 78 86 96 LSB/g
±12 g, 10-bit resolution 39 43 48 LSB/g
, Y
−150 +150 mg
OUT
OUT
−250 +250 mg
OUT
, Y
, Z
OUT
, Y
±0.8 mg/°C
OUT
OUT
±1.5 mg/°C
OUT
−250 +250 mg
OUT
OUT
g
g
g
) 1.7 VS V
DD I/O
Rev. 0 | Page 3 of 32
Page 4
ADXL312
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
Self-test change is defined as the output (g) when the SELF_TEST bit = 1 (in the DATA_FORMAT register) minus the output (g) when the SELF_TEST bit = 0 (in the
DATA_FORMAT register). Due to device filtering, the output reaches its final value after 4 × τ when enabling or disabling self-test, where τ = 1/(data rate).
5
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. 0 | Page 4 of 32
Page 5
ADXL312
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 3.9 V
V
−0.3 V to 3.9 V
DD I/O
All Other Pins
Output Short-Circuit Duration
(Any Pin to Ground)
Temperature Range
Powered −40°C to +125°C
Storage −40°C to +125°C
−0.3 V to V
3.9 V, whichever is less
Indefinite
DD I/O
+ 0.3 V or
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.
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 3. Thermal Resistance
Package Type θJA θ
32-Lead LFCSP Package 27.27 30 °C/W
Unit
JC
ESD CAUTION
Rev. 0 | Page 5 of 32
Page 6
ADXL312
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
DD I/O
NC
V
NCNCNCNCSCL/SCLK
32313029282726
GND
1
GND
GND
NC
V
CS
2
3
4
5
S
6
7
8
ADXL312
TOP VIEW
(Not to S cale)
9
10111213141516
NCNCNCNCNCNCNC
RESERVED
RESERVED
NOTES
1. NC = NO CONNECT. DO NOT CONNECT TO T HIS PIN.
2. THE EXPOSED PAD MUST BE SOL DERED TO THE GROUND PL ANE.
Figure 2. Pin Configuration (Top View)
Table 4. Pin Function Descriptions
Pin No. Mnemonic Description
1 GND This pin must be connected to ground.
2 Reserved Reserved. This pin must be connected to VS or left open.
3 GND This pin must be connected to ground.
4 GND This pin must be connected to ground.
5 VS Supply Voltage.
6
CS
Chip Select.
7 Reserved Reserved. This pin must be left open.
8 to19 NC No Connect. Do not connect to this pin.
20 INT1 Interrupt 1 Output.
21 INT2 Interrupt 2 Output.
22 Reserved Reserved. This pin must be connected to GND or left open.
23 SDO/ALT ADDRESS Serial Data Out, Alternate I2C Address Select.
24 SDA/SDI/SDIO Serial Data (I2C), Serial Data In (SPI 4-Wire), Serial Data In/Out (SPI 3-Wire).
25 NC No Connect. Do not connect to this pin.
26 SCL/SCLK Serial Communications Clock.
27 to 30 NC No Connect. Do not connect to this pin.
31 V
Digital Interface Supply Voltage.
DD I/O
32 NC No Connect.
EP The exposed pad must be soldered to the ground plane.
NC
25
24 SDA/SDI/SDIO
23
SDO/ALT ADDRESS
RESERVED
22
INT2
21
20
INT1
19
NC
18
NC
17 NC
NC
08791-002
Rev. 0 | Page 6 of 32
Page 7
ADXL312
A
A
A
A
A
A
TYPICAL PERFORMANCE CHARACTERISTICS
N>1000 unless otherwise noted.
40
40
35
30
TION (%)
25
20
15
10
PERCENT OF POPUL
5
0
–150 –120 –60 –30–90 0 6030 90 120 150
Figure 3. X-Axis Zero-g Bias. 25°C, V
35
30
25
TION (%)
20
15
10
PERCENT OF PO P UL
5
ZERO g OFFSET (mg)
S
= V
DD I/O
= 3.3 V
35
30
TION (%)
25
20
15
10
PERCENT OF POPUL
5
0
–3.0
–2.5
–2.0
08791-003
–1.5
ZERO g TEMPERATURE COEFFICIENT (mg/°C)
Figure 6. X-Axis Zero-g Bias Drift, V
40
35
30
TION (%)
25
20
15
10
PERCENT OF POPUL
5
0
0.5
1.0
2.0
3.0
2.5
08791-006
S
= V
DD I/O
1.5
= 3.3 V
–1.0
–0.5
0
–150 –120 –60 –30–90 0 6030 90 120 150
Figure 4. Y Axis Zero-g Bias, 25°C, V
50
45
40
35
TION (%)
30
25
20
15
10
PERCENT OF PO P UL
5
0
–250 –200 –100 –50–150 0 10050 150 200 250
Figure 5. Z Axis Zero-g Bias, 25°C, V
ZERO
ZERO
g
OFFSET (mg)
g
OFFSET (mg)
S
S
= V
= V
DD I/O
DD I/O
= 3.3 V
= 3.3 V
08791-004
08791-005
Rev. 0 | Page 7 of 32
0
–3.0
–2.5
–2.0
–1.5
ZERO g TEMPERATURE COEFFICIENT (mg/°C)
–1.0
Figure 7. Y-Axis Zero-g Bias Drift, V
25
20
TION (%)
15
10
5
PERCENT OF POPUL
0
–3.0
–2.5
–2.0
–1.5
ZERO g TEMPERATURE COEFFICIENT (mg/°C)
–1.0
Figure 8. Z-Axis Zero-g Bias Drift, V
0
0.5
1.0
2.0
–0.5
0
–0.5
1.5
= V
= 3.3 V
S
DD I/O
0.5
1.0
1.5
= V
= 3.3 V
S
DD I/O
3.0
2.5
08791-007
2.0
3.0
2.5
08791-008
Page 8
ADXL312
A
A
A
A
A
A
70
60
50
TION (%)
40
30
20
PERCENT OF POPUL
10
0
312
318
324
Figure 9. X-Axis Sensitivity, V
70
60
50
TION (%)
40
330
336
342
SENSITIVITY (LSB/g)
348
354
360
372
384
378
08791-009
S
= V
= 3.3 V, 25°C
DD I/O
366
30
25
20
TION (%)
15
10
PERCENT OF POPUL
5
0
–0.030
–0.025
–0.020
–0.015
SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)
–0.010
–0.005
0
0.005
0.010
0.015
Figure 12. X-Axis Sensitivity Temperature Coefficient, V
35
30
25
TION (%)
20
S
0.020
= V
0.025
DD I/O
0.030
08791-012
= 3.3 V
30
20
PERCENT OF POPUL
10
0
312
318
324
330
Figure 10. Y-Axis Sensitivity, V
70
60
50
TION (%)
40
30
20
PERCENT OF POPUL
10
0
312
318
324
330
Figure 11. Z-Axis Sensitivity, V
336
342
348
354
SENSITIVITY (LSB/g)
= V
S
DD I/O
336
342
348
354
SENSITIVITY (LSB/g)
= V
S
DD I/O
360
372
366
= 3.3 V, 25°C
360
372
366
= 3.3 V, 25°C
15
10
PERCENT OF POPUL
5
0
384
378
08791-010
–0.030
–0.025
–0.020
–0.015
SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)
Figure 13. Y-Axis Sensitivity Temperature Coefficient, V
35
30
25
TION (%)
20
15
10
PERCENT OF POPUL
5
0
384
378
08791-011
–0.030
–0.025
–0.020
–0.015
SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)
Figure 14. Z-Axis Sensitivity Temperature Coefficient, V
–0.010
–0.010
–0.005
–0.005
0
0.005
0.010
0.020
0.015
= V
S
0
0.005
0.010
0.015
= V
S
0.030
0.025
08791-013
= 3.3 V
DD I/O
0.020
0.030
0.025
08791-014
= 3.3 V
DD I/O
Rev. 0 | Page 8 of 32
Page 9
ADXL312
A
A
A
A
A
80
80
70
60
TION (%)
50
40
30
20
PERCENT OF POPUL
10
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SELF-TEST RESPONSE (g)
Figure 15. X-Axis Self-Test Delta, V
70
60
50
TION (%)
40
30
20
PERCENT OF POPUL
10
S
= V
DD I/O
= 3.3 V, 25°C
70
60
TION (%)
50
40
30
20
PERCENT OF POPUL
10
0
08791-015
305070
Figure 18. Standby Mode Current Consumption, V
35
30
25
TION (%)
20
15
10
PERCENT OF POPUL
5
90
110
130
CURRENT (nA)
150
170
190
210
230
S
= V
250
270
= 3.3 V, 25°C
DD I/O
290
310
08791-018
0
–2.1
–1.9
–1.7
–1.5
–1.3
SELF-TEST RESPONSE (g)
Figure 16. Y-Axis Self-Test Delta, V
80
70
60
TION (%)
50
40
30
20
PERCENT OF POPUL
10
0
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.33.0
SELF-TEST RESPONSE (g)
Figure 17. Z-Axis Self-Test Delta, V
–1.1
= V
S
= V
S
–0.9
DD I/O
DD I/O
–0.7
–0.5
= 3.3 V, 25°C
= 3.3 V, 25°C
–0.3
08791-016
08791-017
0
100
120
140
160
180
200
220
240
260
280
CURRENT CONSUMPTION (µA)
300
8791-019
Figure 19. Current Consumption, Measurement Mode, Data Rate = 100 Hz,
V
= V
= 3.3 V, 25°C
S
DD I/O
200
150
100
SUPPLY CURRENT (µA)
50
0
2.0 2.4 2.8 3.2 3.6
SUPPLY VOLTAGE (V)
Figure 20. Supply Current vs. Supply Voltage, V
at 25°C
S
08791-233
Rev. 0 | Page 9 of 32
Page 10
ADXL312
THEORY OF OPERATION
The ADXL312 is a complete 3-axis acceleration measurement
system with a selectable measurement range of ±1.5 g, ±3 g, ±6
g, or ±12 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. Phasesensitive demodulation is used to determine the magnitude and
polarity of the acceleration.
POWER SEQUENCING
Power can be applied to VS or V
damaging the ADXL312. All possible power-on modes are
summarized in Tab le 5 . The interface voltage level is set with
the interface supply voltage, V
ensure that the ADXL312 does not create a conflict on the
communication bus. For single-supply operation, V
the same as the main supply, V
however, V
can differ from VS to accommodate the desired
DD I/O
interface voltage, as long as V
After V
is applied, the device enters standby mode, where power
S
consumption is minimized and the device waits for V
applied and for the command to enter measurement mode to be
received. (This command can be initiated by setting the measure
bit 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.
in any sequence without
DD I/O
, which must be present to
DD I/O
DD I/O
. In a dual-supply application,
S
is greater than or equal to V
S
DD I/O
can be
.
DD I/O
to be
Table 5. Power Sequencing
Condition VS V
Power Off Off Off
Bus Disabled On Off
Bus Enabled Off On
Standby or
Measurement
On On
Description
DD I/O
The device is completely off, but
there is a potential for a
communication bus conflict.
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.
No functions are available, but
the device will not create a conflict
on the communication bus.
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.
POWER SAVINGS
Power Modes
The ADXL312 automatically modulates its power consumption
in proportion to its output data rate, as outlined in Tab le 6 . 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 4) in the BW_RATE
register (Address 0x2C). The current consumption in low power
mode is shown in Tabl e 7 for cases where there is an advantage
to using low power mode. Use of low power mode for a data
rate not shown in Tab le 7 does not provide any advantage over
the same data rate in normal power mode. Therefore, it is
recommended that only data rates shown in Tab le 7 be used in
low power mode. The current consumption values shown in
Table 6 and Tab le 7 are for a V
of 3.3 V.
S
Rev. 0 | Page 10 of 32
Page 11
ADXL312
Table 6. Current Consumption vs. Data Rate
= 25°C, VS = V
(T
A
Output Data
Rate (Hz) Bandwidth (Hz) Rate Code I
3200 1600 1111 170
1600 800 1110 115
800 400 1101 170
400 200 1100 170
200 100 1011 170
100 50 1010 170
50 25 1001 115
25 12.5 1000 82
12.5 6.25 0111 65
6.25 3.125 0110 57
DD I/O
= 3.3 V)
DD
(μA)
Table 7. Current Draw vs. Data Rate, Low Power Mode
= 25°C, VS = V
(T
A
Output Data
Rate (Hz) Bandwidth (Hz) Rate Code I
400 200 1100 115
200 100 1011 82
100 50 1010 65
50 25 1001 57
25 12.5 1000 50
12.5 6.25 0111 43
DD I/O
= 3.3 V)
DD
(μA)
Autosleep Mode
Additional power savings can be had by having the ADXL312
automatically switch to sleep mode during periods of inactivity.
To enable this feature, set the THRESH_INACT register
(Address 0x25) to an acceleration threshold value. Levels of
acceleration below this threshold are regarded as no activity
levels. Set TIME_INACT (Address 0x26) to an appropriate
inactivity time period. Then set the AUTO_SLEEP bit and the
link bit in the POWER_CTL register (Address 0x2D). If the
device does not detect a level of acceleration in excess of
THRES_INACT for TIME_INACT seconds, then the device is
transitioned to sleep mode automatically. Current consumption
at the sub-8 Hz data rates used in this mode is typically 30 µA
for a V
of 3.3 V.
S
Standby Mode
For even lower power operation, standby mode can be used. In
standby mode, current consumption is reduced to 0.1µA
(typical). In this mode, no measurements are made. Standby
mode is entered by clearing the measure bit (Bit 3) in the
POWER_CTL register (Address 0x2D). Placing the device into
standby mode preserves the contents of the FIFO.
Rev. 0 | Page 11 of 32
Page 12
ADXL312
SERIAL COMMUNICATIONS
I2C and SPI digital communications are available. In both cases,
the ADXL312 operates as a slave. I
is tied high to V
V
or be driven by an external controller because there is no
DD I/O
default mode if the
. The CS pin should always be tied high to
DD I/O
CS
pin is left unconnected. Therefore, not
taking these precautions may result in an inability to communicate
with the part. In SPI mode, the
master. In both SPI and I
2
C modes of operation, data transmitted
from the ADXL312 to the master device should be ignored during
writes to the ADXL312.
SPI
For SPI, either 3- or 4-wire configuration is possible, as shown
in the connection diagrams in Figure 21 and Figure 22. Clearing
the SPI bit 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
ADXL312 before the clock polarity and phase of the host
processor are configured, the
before changing the clock polarity and phase. When using 3-wire
SPI, it is recommended that the SDO pin be either pulled up to
V
or pulled down to GND via a 10 kΩ resistor.
DD I/O
ADXL312
CS
SDIO
SDO
SCLK
Figure 21. 3-Wire SPI Connection Diagram
ADXL312
CS
SDI
SDIO
SCLK
Figure 22. 4-Wire SPI Connection Diagram
2
C mode is enabled if the CS pin
CS
pin is controlled by the bus
CS
pin should be brought high
PROCESSOR
D OUT
D IN/OUT
D OUT
PROCESSOR
D OUT
D OUT
D IN
D OUT
08791-021
08791-022
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 . SCLK is the
Figure 23
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/
Figure 23 Figure 25
(MB in to ), must be set. After the register
W
bit in the first byte transfer
addressing and the first byte of data, each subsequent set of
clock pulses (eight clock pulses) causes the ADXL312 to point
to the next register for a read or write. This shifting continues
until the clock pulses cease and
or writes on different, nonsequential registers,
CS
is deasserted. To perform reads
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 25. The 4-wire equivalents for SPI writes and reads are
shown in Figure 23 and Figure 24, respectively. For correct
operation of the part, the logic thresholds and timing
parameters in Table 8 and Table 9 must be met at all times.
Use of the 3200 Hz and 1600 Hz output data rates is only
recommended 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
below the recommended minimum may result in undesirable
effects on the acceleration data, including missing samples or
additional noise.
Rev. 0 | Page 12 of 32
Page 13
ADXL312
Table 8. SPI Digital Input/Output
Limit1
Parameter Test Conditions Min Max Unit
Digital Input
Low Level Input Voltage (VIL) 0.3 × V
High Level Input Voltage (VIH) 0.7 × V
Low Level Input Current (IIL) VIN = V
0.1 μA
DD I/O
V
DD I/O
High Level Input Current (IIH) VIN = 0 V −0.1 μA
Digital Output
Low Level Output Voltage (VOL) IOL = 10 mA 0.2 × V
High Level Output Voltage (VOH) IOH = −4 mA 0.8 × V
Low Level Output Current (IOL) VOL = V
High Level Output Current (IOH) VOH = V
10 mA
OL, max
−4 mA
OH, min
V
DD I/O
Pin Capacitance fIN = 1 MHz, VIN = 2.5 V 8 pF
1
Limits based on characterization results, not production tested.
V
DD I/O
V
DD I/O
Table 9. SPI Timing (TA = 25°C, VS = V
Limit
2, 3
= 3.3 V)1
DD I/O
Parameter Min Max Unit Description
f
5 MHz SPI clock frequency.
SCLK
t
200 ns 1/(SPI clock frequency) mark-space ratio for the SCLK input is 40/60 to 60/40.
SCLK
t
5 ns
DELAY
t
5 ns
QUIET
t
10 ns
DIS
t
150 ns
CS,DIS
tS 0.3 × t
tM 0.3 × t
t
5 ns SDI valid before SCLK rising edge.
SETUP
t
5 ns SDI valid after SCLK rising edge.
HOLD
t
40 ns SCLK falling edge to SDO/SDIO output transition.
SDO
4
t
20 ns SDO/SDIO output high to output low transition.
R
4
t
20 ns SDO/SDIO output low to output high transition.
F
1
The CS, SCLK, SDI, and SDO pins are not internally pulled up or down; they must be driven for proper operation.
2
Limits based on characterization results, characterized with f
3
The timing values are measured corresponding to the input thresholds (VIL and VIH) given in Table 8.
4
Output rise and fall times measured with capacitive load of 150 pF.
ns SCLK low pulse width (space).
SCLK
ns SCLK high pulse width (mark).
SCLK
falling edge to SCLK falling edge .
CS
SCLK rising edge to CS
rising edge to SDO disabled.
CS
deassertion between SPI communications.
CS
= 5 MHz and bus load capacitance of 100 pF; not production tested.
SCLK
rising edge.
Rev. 0 | Page 13 of 32
Page 14
ADXL312
SCLK
K
K
CS
t
DELAY
t
SCLK
t
MtS
t
QUIET
t
CS,DIS
SDI
SDO
t
SETUP
W
XXX
t
HOLD
MB A5 A0 D7 D0
t
SDO
ADDRESS BITS DATA BITS
XX X
t
,
t
R
F
Figure 23. SPI 4-Wire Write
t
DIS
08791-129
CS
SCL
SDI
SDO
t
SETUP
t
t
t
HOLD
SDO
SCLK
ADDRESS BITS
t
DELAY
RMBA5
XXX
t
t
M
S
A0
t
,
t
R
F
X
D7
DATA BITS
t
QUIET
X
t
DIS
D0X
t
CS,DIS
08791-130
Figure 24. SPI 4-Wire Read
CS
t
DELAY
SCL
t
SETUP
SDIO
SDO
NOTES
1.
t
IS ONLY P RE S E NT DURI NG READS.
SDO
t
t
SCLK
t
HOLD
R/W MB A5 A0 D7 D0
ADDRESS BITS DATA BITS
t
,
R
t
M
S
t
t
F
SDO
t
QUIET
Figure 25. SPI 3-Wire Read/Write
t
CS,DIS
08791-131
Rev. 0 | Page 14 of 32
Page 15
ADXL312
V
R
DD I/O
P
R
P
PROCESSOR
D IN/OUT
D OUT
08791-032
DD I/O
, are necessary
P
I2C
With CS tied high to V
requiring a simple 2-wire connection as shown in .
The ADXL312 conforms to the UM10204 I
and User Manual, Rev. 03—19 June 2007, available from NXP
Semiconductor. It supports standard (100 kHz) and fast (400 kHz)
data transfer modes if the bus parameters given in and
Table 11
are met. Single- or multiple-byte reads/writes are
supported, as shown in . With the ALT ADDRESS pin
high, the 7-bit I
W
R/
bit. This translates to 0x3A for a write and 0x3B for a read. An
alternate I
2
C address for the device is 0x1D, followed by the
2
C address of 0x53 (followed by the R/W bit) can be
chosen by grounding the ALT ADDRESS pin (Pin 7). This
translates to 0xA6 for a write and 0xA7 for a read.
, the ADXL312 is in I2C mode,
DD I/O
2
C-Bus Specification
Figure 27
Figure 26
Table 10
ADXL312
CS
SDA
ALT ADDRESS
SCL
Figure 26. I
2
C 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 V
by more than 0.3 V. External pull-up resistors, R
for proper I
2
C 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.
2
Table 10. I
C Digital Input/Output
Limit1
Parameter Test Conditions Min Max Unit
Digital Input
Low Level Input Voltage (VIL) 0.3 × V
High Level Input Voltage (VIH) 0.7 × V
Low Level Input Current (IIL) VIN = V
0.1 μA
DD I/O
V
DD I/O
V
DD I/O
High Level Input Current (IIH) VIN = 0 V −0.1 μA
Digital Output
Low Level Output Voltage (VOL) V
V
Low Level Output Current (IOL) VOL = V
< 2 V, IOL = 3 mA 0.2 × V
DD I/O
≥ 2 V, IOL = 3 mA 400 mV
DD I/O
3 mA
OL, max
DD I/O
V
Pin Capacitance fIN = 1 MHz, VIN = 2.5 V 8 pF
1
Limits based on characterization results; not production tested.
SINGLE-BYTE W RITE
MASTER START SLAVE ADDRESS + WRI T E REGISTER ADDRESS
SLAVE ACK ACK ACK
MULTIPLE-BYTE WRI TE
MASTER START SLAVE ADDRESS + WRI T E REGISTER ADDRESS
SLAVE ACK ACK ACK ACK
SINGLE- BYTE READ
MASTER START SLAVE ADDRESS + WRI T E REGISTER ADDRESS STOP
SLAVE ACK ACK
MULTIPLE- BY TE RE AD
MASTER START
SLAVE ACK ACK
NOTES
1. THIS START IS EITHER A RESTART OR A STOP FOLLOWED BY A START.
2. THE SHADED AREAS RE P RE S E NT WHEN THE DEV ICE IS LISTENING .
SLAVE ADDRESS + WRI T E REGISTER ADDRESS NACK STOP
Figure 27. I
START
START
1
1
DATA
DATA
SLAVE ADDRESS + READ
SLAVE ADDRESS + READ
2
C Device Addressing
STOP
ACK
ACK
DATA
DATA
DATA
STOP
NACK
ACK
DATA
08791-033
Rev. 0 | Page 15 of 32
Page 16
ADXL312
S
Table 11. I2C Timing (TA = 25°C, VS = V
Limit
Parameter Min Max Unit Description
f
400 kHz SCL clock frequency
SCL
t1 2.5 μs SCL cycle time
t2 0.6 μs t
t3 1.3 μs t
t4 0.6 μs t
t5 100 ns t
3, 4, 5, 6
t
0 0.9 μs t
6
t7 0.6 μs t
t8 0.6 μs t
t9 1.3 μs t
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 250 ns tF, fall time of SDA when receiving
300 ns tF, fall time of both SCL and SDA when transmitting
20 + 0.1 C
7
ns tF, fall time of both SCL and SDA when transmitting or receiving
b
Cb 400 pF Capacitive load for each bus line
1
Limits based on characterization results, with f
2
All values referred to the VIH and the VIL levels given in Table 10.
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 V
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 (t
t
= t3 − t10 − t
6(max)
7
C
is the total capacitance of one bus line in picofarads.
b
5(min)
.
= 3.3 V)
DD I/O
1, 2
, SCL high time
HIGH
, SCL low time
LOW
, start/repeated start condition hold time
HD, STA
, data setup time
SU, DAT
, data hold time
HD, DAT
, setup time for repeated start
SU, STA
, stop condition setup time
SU, STO
, bus-free time between a stop condition and a start condition
BUF
= 400 kHz and a 3 mA sink current; not production tested.
SCL
of the SCL signal) to bridge the
IH(min)
). This value is calculated as
5(min)
DA
SCL
t
9
t
4
START
CONDITION
t
3
t
10
t
6
t
Figure 28. I
2
2
t
11
t
5
C Timing Diagram
REPEATED
CONDITION
t
7
START
t
4
t
1
t
8
STOP
CONDITION
08791-034
Rev. 0 | Page 16 of 32
Page 17
ADXL312
INTERRUPTS
The ADXL312 provides two output pins for driving interrupts:
INT1 and INT2. Both interrupt pins are push-pull, low impedance
pins with output specifications shown in Tabl e 12 . 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. 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
register (Address 0x2F). When initially configuring the interrupt
pins, it is recommended that the functions and interrupt mapping
be done before enabling the interrupts. When changing the configuration 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 desired.
The interrupt functions are latched and cleared by either reading
the data 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 register (Address 0x30) for the
remaining interrupts. This section describes the interrupts that
can be set in the INT_ENABLE register and monitored in the
INT_SOURCE register.
Table 12. Interrupt Pin Digital Output
Limit1
Parameter Test Conditions Min Max Unit
Digital Output
Low Level Output Voltage (VOL) IOL = 300 μA 0.2 × V
High Level Output Voltage (VOH) IOH = −150 μA 0.8 × V
Low Level Output Current (IOL) VOL = V
High Level Output Current (IOH) VOH = V
Pin Capacitance fIN = 1 MHz, VIN = 2.5 V 8 pF
Rise/Fall Time
Rise Time (tR)2 C
Fall Time (tF)3 C
1
Limits based on characterization results, not production tested.
2
Rise time is measured as the transition time from V
3
Fall time is measured as the transition time from V
OL, max
OH, min
to V
to V
LOAD
LOAD
OH, min
OL, max
300 μA
OL, max
OH, min
= 150 pF 210 ns
= 150 pF
of the interrupt pin.
of the interrupt pin.
DATA_READY
The DATA_READY bit is set when new data is available and is
cleared when no new data is available.
Activity
The activity bit is set when acceleration greater than the value stored
in the THRESH_ACT register (Address 0x24) is experienced.
Inactivity
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
register (Address 0x26). The maximum value for TIME_INACT is
255 sec.
Watermark
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.
Overrun
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.
V
DD I/O
V
DD I/O
−150 μA
150 ns
Rev. 0 | Page 17 of 32
Page 18
ADXL312
FIFO
The ADXL312 contains patent pending 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 2 1).
Each mode is selected by the settings of the FIFO_MODE bits
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
register (Address 0x38), the watermark interrupt is set. FIFO
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 activity 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 zaxes are stored in FIFO. When the number of samples in FIFO
equals the level specified in the samples bits of the FIFO_CTL
register (Address 0x38), the watermark interrupt is set. FIFO
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 s 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 is
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 s 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
from Register 0x37 to Register 0x38 or by the
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
delay of 5 s; otherwise, the delay will not be sufficient. The total
delay necessary for 5 MHz operation is at most 3.4 s. This is
not a concern when using I
rate is low enough to ensure a sufficient delay between FIFO reads.
2
C mode because the communication
CS
pin going high.
CS
pin to ensure a total
Rev. 0 | Page 18 of 32
Page 19
ADXL312
SELF-TEST
The ADXL312 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. This electrostatic force
moves the mechanical sensing element in the same manner as
acceleration, 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 V
effect is shown in Figure 29. The scale factors shown in Table 13
can be used to adjust the expected self-test output limits for
different supply voltages, V
also exhibits a bimodal behavior. However, the limits shown in
Table 1 and Tab le 14 to Tabl e 17 are valid for both potential selftest values due to bimodality. 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 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.
6
4
2
2
, the output change varies with VS. This
S
. The self-test feature of the ADXL312
S
Table 13. Self-Test Output Scale Factors for Different Supply
Voltages, V
S
Supply Voltage, VS X-, Y-Axes Z-Axis
2.00 V 0.64 0.8
2.50 V 1.00 1.00
3.00 V 1.77 1.47
3.30 V 2.11 1.69
Table 14. Self-Test Output in LSB for ±1.5 g, 10-Bit or Full
Resolution (T
= 25°C, VS = V
A
DD I/O
= 2.5 V)
Axis Min Max Unit
X 65 725 LSB
Y −725 −65 LSB
Z 100 1175 LSB
Table 15. Self-Test Output in LSB for ±3 g, 10-Bit Resolution
= 25°C, VS = V
(T
A
DD I/O
= 2.5 V)
Axis Min Max Unit
X 32 362 LSB
Y −362 −32 LSB
Z 50 588 LSB
Table 16. Self-Test Output in LSB for ±6 g, 10-Bit Resolution
(T
= 25°C, VS = V
A
DD I/O
= 2.5 V)
Axis Min Max Unit
X 16 181 LSB
Y −181 −16 LSB
Z 25 294 LSB
0
–2
SELF-TEST SHIFT LIMIT (g)
X HIGH
X LOW
Y HIGH
–4
Y LOW
Z HIGH
Z LOW
–6
2.0 2.5 3.3 3.6
(V)
V
S
Figure 29. Self-Test Output Change Limits vs. Supply Voltage
Table 17. Self-Test Output in LSB for ±12 g, 10-Bit
Resolution (T
= 25°C, VS = V
A
DD I/O
= 2.5 V)
Axis Min Max Unit
X 8 90 LSB
Y −90 −8 LSB
Z 12 147 LSB
08791-242
Rev. 0 | Page 19 of 32
Page 20
ADXL312
REGISTER MAP
Table 18. Register Map
Address
Hex Dec Name Type Reset Value Description
0x00 0 DEVID R 11100101 Device ID.
0x01 to 0x1D 1 to 29 Reserved Reserved. Do not access.
0x1E 30 OFSX
0x1F 31 OFSY
0x20 32 OFSZ
0x21 33 Reserved Reserved. Do not access.
0x22 34 Reserved Reserved. Do not access.
0x23 35 Reserved Reserved. Do not access.
0x24 36 THRESH_ACT
0x25 37 THRESH_INACT
0x26 38 TIME_INACT
0x27 39 ACT_INACT_CTL
0x28 40 Reserved Reserved. Do not access.
0x29 41 Reserved Reserved. Do not access.
0x2A 42 Reserved Reserved. Do not access.
0x2B 43 Reserved Reserved. Do not access.
0x2C 44 BW_RATE
0x2D 45 POWER_CTL
0x2E 46 INT_ENABLE
0x2F 47 INT_MAP
0x30 48 INT_SOURCE R 00000010 Source of interrupts.
0x31 49 DATA_FORMAT
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
0x39 57 FIFO_STATUS R 00000000 FIFO status.
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
00000000 X-axis offset.
00000000 Y-axis offset.
00000000 Z-axis offset.
00000000 Activity threshold.
00000000 Inactivity threshold.
00000000 Inactivity time.
00000000 Axis enable control for activity and inactivity detection.
00001010 Data rate and power mode control.
00000000 Power-saving features control.
00000000 Interrupt enable control.
00000000 Interrupt mapping control.
00000000 Data format control.
00000000 FIFO control.
Rev. 0 | Page 20 of 32
Page 21
ADXL312
REGISTER DEFINITIONS
Register 0x00—DEVID (Read Only)
D7 D6 D5 D4 D3 D2 D1 D0
1 1 1 0 0 1 0 1
The DEVID register holds a fixed device ID code of 0xE5.
Register 0x1E, Register 0x1F, Register 0x20—OFSX, 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 11.6 mg/LSB (that is, 0x7F = +1.5 g). The
value stored in the offset registers is automatically added to the
acceleration data, and the resulting value is stored in the output
data registers.
Register 0x24—THRESH_ACT (Read/Write)
The THRESH_ACT register is eight bits and holds the threshold
value for detecting activity. The data format is unsigned;
therefore, the magnitude of the activity event is compared with
the value in the THRESH_ACT register. The scale factor is
46.4 mg/LSB.
A value of 0 may result in undesirable behavior if the activity
interrupt is enabled.
Register 0x25—THRESH_INACT (Read/Write)
The THRESH_INACT register is eight bits and holds the threshold
value for detecting inactivity. The data format is unsigned;
therefore, the magnitude of the inactivity event is compared
with the value in the THRESH_INACT register. The scale factor is
46.4 mg/LSB. A value of 0 may result in undesirable behavior if
the inactivity interrupt is enabled.
Register 0x26—TIME_INACT (Read/Write)
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.
Register 0x27—ACT_INACT_CTL (Read/Write)
D7 D6 D5 D4
ACT ac/dc ACT_X enable ACT_Y enable ACT_Z enable
D3 D2 D1 D0
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.
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 participating 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.
Register 0x2C—BW_RATE (Read/Write)
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 has
somewhat higher noise (see the Power Modes section for details).
Rate Bits
These bits select the device bandwidth and output data rate (see
Table 6 and Tabl e 7 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 communica-tion
protocol and frequency selected. Selecting too high of an output
data rate with a low communication speed results in samples
being discarded.
Register 0x2D—POWER_CTL (Read/Write)
D7 D6 D5 D4 D3 D2 D1 D0
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,
Rev. 0 | Page 21 of 32
Page 22
ADXL312
the inactivity and activity functions are concurrent. Additional
information can be found in the Link Mode section.
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 sets
the ADXL312 to switch to sleep mode when inactivity is detected
(that is, when acceleration has been below the THRESH_INACT
value for at least the time indicated by TIME_INACT). A setting
of 0 disables automatic switching to sleep mode. See the description
of the sleep bit in this section for more information.
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. 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
ADXL312 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 (see Register 0x2E, Register
0x2F, and Register 0x30), stops transmission of data to FIFO, and
switches the sampling rate to one specified by the wake-up bits.
In sleep mode, only the activity function can be used.
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.
Wak e- U p Bi t s
These bits control the frequency of readings in sleep mode as
described in Table 19.
Table 19. Frequency of Readings in Sleep Mode
Setting
D1 D0 Frequency (Hz)
0 0 8
0 1 4
1 0 2
1 1 1
Register 0x2E—INT_ENABLE (Read/Write)
D7 D6 D5 D4
DATA_READY N/A N/A Activity
D3 D2 D1 D0
Inactivity N/A Watermark Overrun
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 bits enable only the interrupt output;
the functions are always enabled. It is recommended that interrupts
be configured before enabling their outputs.
Register 0x2F—INT_MAP (Read/Write)
D7 D6 D5 D4
DATA_READY N/A N/A Activity
D3 D2 D1 D0
Inactivity N/A Watermark Overrun
Any 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.
Register 0x30—INT_SOURCE (Read Only)
D7 D6 D5 D4
DATA_READY N/A N/A Activity
D3 D2 D1 D0
Inactivity N/A Watermark Overrun
Bits set to 1 in this register indicate that their respective functions
have triggered an event, whereas a value of 0 indicates that the
corresponding event has not occurred. The DATA_READY,
watermark, and overrun bits are always set if the corresponding
events occur, regardless of the INT_ENABLE register settings,
and are cleared by reading data from the 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,
are cleared by reading the INT_SOURCE register.
Rev. 0 | Page 22 of 32
Page 23
ADXL312
Register 0x31—DATA_FORMAT (Read/Write)
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 ±12 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 2.9 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 (MSB) justified mode,
and a setting of 0 selects right justified mode with sign extension.
Range Bits
These bits set the g range as described in Tabl e 20 .
Table 20. g Range Setting
Setting
D1 D0 g Range
0 0 ±1.5 g
0 1 ±3 g
1 0 ±6 g
1 1 ±12 g
Register 0x32 to Register 0x37—DATAX0, DATAX1, 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
Register 0x33 hold the output data for the x-axis, Register 0x34 and
Register 0x35 hold the output data for the y-axis, and Register 0x36
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
represent 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.
Register 0x38—FIFO_CTL (Read/Write)
D7 D6 D5 D4 D3 D2 D1 D0
FIFO_MODE Trigger Samples
FIFO_MODE Bits
These bits set the FIFO mode, as described in Tabl e 21.
Table 21. FIFO Modes
Setting
D7 D6 Mode Function
0 0 Bypass FIFO is bypassed.
0 1 FIFO
1 0 Stream
1 1 Trigger
FIFO collects up to 32 values and then
stops collecting data, collecting new data
only when FIFO is not full.
FIFO holds the last 32 data values. When
FIFO is full, the oldest data is overwritten
with newer data.
When triggered by the trigger bit, FIFO
holds the last data samples before the
trigger event and then continues to collect
data until 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
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 22). Entering a value of 0 in the samples bits
immediately sets the watermark status bit in the INT_SOURCE
register, 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 22. Samples Bits Functions
FIFO Mode Samples Bits Function
Bypass None.
FIFO
Stream
Trigger
Specifies how many FIFO entries are needed to
trigger a watermark interrupt.
Specifies how many FIFO entries are needed to
trigger a watermark interrupt.
Specifies how many FIFO samples are retained in
the FIFO buffer before a trigger event.
Rev. 0 | Page 23 of 32
Page 24
ADXL312
0x39—FIFO_STATUS (Read Only)
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.
Rev. 0 | Page 24 of 32
Page 25
ADXL312
V
V
APPLICATIONS INFORMATION
POWER SUPPLY DECOUPLING
A 1 F tantalum capacitor (CS) at VS and a 0.1 F ceramic capacitor
(C
I/O
) at V
placed close to the ADXL312 supply pins is
DD I/O
recommended to adequately decouple the accelerometer from
noise on the power supply. If additional decoupling is necessary,
a resistor or ferrite bead, no larger than 100 Ω, in series with V
may be helpful. Additionally, increasing the bypass capacitance
on V
to a 10 F tantalum capacitor in parallel with a 0.1 F
S
ceramic capacitor may also improve noise.
Care should be taken to ensure that the connection from the
ADXL312 ground to the power supply ground has low impedance
because noise transmitted through ground has an effect similar
to noise transmitted through V
be separate supplies to minimize digital clocking noise
V
DD I/O
on the V
supply. If this is not possible, additional filtering of
S
. It is recommended that VS and
S
the supplies as previously mentioned may be necessary.
INTERRUPT
CONTROL
S
C
S
V
S
ADXL312
SDO/ALT ADDRES S
INT1
INT2
Figure 30. Application Diagram
DD I/O
V
DD I/O
SDA/SDI/SDIO
SCL/SCLK
GND
CS
C
I/O
3-WIRE OR
4-WIRE SPI
2
OR I
C
INTERFACE
08791-035
MECHANICAL CONSIDERATIONS FOR MOUNTING
The ADXL312 should be mounted on the PCB in a location
close to a hard mounting point of the PCB to the case. Mounting
the ADXL312 at an unsupported PCB location, as shown in
Figure 31, 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.
ACCELEROMETERS
PCB
S
THRESHOLD
The lower output data rates are achieved by decimating a
common sampling frequency inside the device. The activity
detection function is performed using undecimated data.
Because 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 are used to determine
activity 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.
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
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.
However, when sleep mode is used in conjunction with the
autosleep 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 ADXL312 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.
MOUNTING POINT S
Figure 31. Incorrectly Placed Accelerometers
08791-036
Rev. 0 | Page 25 of 32
Page 26
ADXL312
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 ADXL312 is also necessary for an
accurate self-test measurement. The part should be set with a
data rate greater than or equal to 100 Hz. This is done by
ensuring that a value greater than or equal to 0x0A is written
into the rate bits (Bit D3 through Bit D0) in the BW_RATE
register (Address 0x2C). The part also must be placed into
normal power operation by ensuring the LOW_POWER bit 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, 12 g mode to ensure that there is
sufficient dynamic range for the entire self-test shift. This is done
by setting Bit D3 of the DATA_FORMAT register (Address 0x31)
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 2.9 mg/LSB scale factor.
After the part is configured for accurate self-test measurement,
several samples of x-, y-, and z-axis acceleration data 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, which corresponds
to 10 samples at 100 Hz data rate. The averaged values should
be stored and labeled appropriately as the self-test disabled data,
that is, X
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 after enabling self-test.
After allowing the output to settle, several samples of the x-, y-,
and z-axis acceleration data should be taken again and averaged. It
ST_OFF
, Y
ST_OFF
, and Z
ST_OFF
.
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 selftest enabled, that is, X
ST_ON
, Y
ST_ON
, and Z
. Self-test can then
ST_ON
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:
X
= X
ST
Y
= Y
ST
Z
= Z
ST
ST_ON
ST_ON
ST_ON
− X
− Y
− Z
ST_OFF
ST_OFF
ST_OFF
Because the measured output for each axis is expressed in LSBs,
X
, YST, and ZST are also expressed in LSBs. These values can be
ST
converted to g’s of acceleration by multiplying each value by the
2.9 mg/LSB scale factor, if configured for full-resolution mode.
Additionally, Table 14 through Table 17 correspond to the selftest range converted to LSBs and can be compared with the
measured self-test change when operating at a V
of 3.3 V. For
S
other voltages, the minimum and maximum self-test output
values should be adjusted based on (multiplied by) the scale
factors shown in Table 13. If the part was placed into ±1.5 g,
10-bit or full-resolution mode, the values listed in Table 14 should
be used. Although the fixed 10-bit mode or a range other than
12 g can be used, a different set of values, as indicated in Table 15
through Tabl e 17 , must be used. Using a range below 6 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.
Rev. 0 | Page 26 of 32
Page 27
ADXL312
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.
When in full-resolution or ±1.5 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 32. When data is left justified and the part is operating in
±1.5 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 ±1.5 g, the LSB is Bit D6 of
DATAx1 REGIS TER DATAx0 REGISTER
D0D1D2D3D4D5D6D7
D0D1D2D3D4D5D6D7
the DATAx0 register; for ±3 g, Bit D5 of the DATAx0 register;
for ±6 g, Bit D4 of the DATAx0 register; and for ±12 g, Bit D3
of the DATAx0 register. This is shown in Figure 33.
The use of 3200 Hz and 1600 Hz output data rates for fixed 10-bit
operation in the ±3 g, ±6 g, and ±12 g output ranges provides an
LSB that is valid and that changes according to the applied acceleration. 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 changes according to the applied acceleration.
D0D1D2D3D4D5D6D7
0D1D2D3D4D5D6D7
OUTPUT DAT A-WORD FOR
±12g, FULL-RESOLUTION MODE.
THE ±3g AND ±6g FULL-RESOLUTION MODE S HAV E THE SAME LSB LOCATION AS THE±1.5g
AND ±12g FUL L-RESOLUTION MODE S , BUT THE MSB LOCATIO N CHANGES TO BI T D2 AND
BIT D3 OF THE DATAx1 REGI S TER FOR ±3g AND ±6 g, RESPECTIVELY.
OUTPUT DAT A-WORD FOR ±1.5g, 10-BIT
AND ±1.5g, FULL-RESOLUTIO N MODES.
8791-145
Figure 32. Data Formatting of Full-Resolution and ±1.5 g, 10-Bit Modes of Operation When Output Data Is Right Justified
DATAx1 REGIS TER DATAx0 REGI S TER
D0D1D2D3D4D5D6D7
D0D1D2D3D4D5D6D7
LSB FOR ±1. 5g, FULL-RESOLUTION
MSB FOR ALL MODES
OF OPERATION WHEN
LEFT JUSTIFIED.
FOR 3200Hz AND 1600Hz O UTPUT DATA RAT E S , THE LSB IN THESE MODES IS AL WAYS 0.
ADDITIONALLY, ANY BI TS TO T HE RIGHT OF THE LSB ARE ALWAYS 0 WHEN T HE OUTPUT
DATA IS LEFT JUSTI FIED.
AND ±1.5g, 10-BIT MODES.
LSB FOR ±3g, FULL-RESOLUT I ON MODE.
LSB FOR ±6g, FULL-RESOLUT I ON MODE.
LSB FOR ±12g, FULL-RESOL UT ION MODE.
D0D1D2D3D4D5D6D7
0D1D2D3D4D5D6D7
08791-146
Figure 33. Data Formatting of Full-Resolution and ±1.5 g, 10-Bit Modes of Operation When Output Data Is Left Justified
Rev. 0 | Page 27 of 32
Page 28
ADXL312
A
NOISE PERFORMANCE
The specification of noise shown in Table 1 corresponds to the
best case noise of the ADXL312 in normal power operation
(LOW_POWER bit = 0 in BW_RATE register, Address 0x2C).
For normal power operation at data rates below 100 Hz, the
noise of the ADXL312 is equivalent to the noise at 100 Hz ODR
in LSBs. For data rates greater than 100 Hz, the noise increases
roughly 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 2.0 LSB rms and the noise on the z-axis is
typically less than 3.0 LSB rms.
For low power operation (LOW_POWER bit = 1 in BW_RATE
register, Address 0x2C) the noise of the ADXL312 is constant
for all valid data rates shown in Tabl e 7. This value is typically
less than 2.4 LSB rms for the x- and y-axes and typically less
than 3.5 LSB rms for the z-axis.
Figure 34 shows the typical Allan deviation for the ADXL312.
The 1/f corner of the device, as shown in this figure, is very low,
allowing absolute resolution of approximately 100 µg (assuming
there is sufficient integration time). The figure also shows that the
noise density is 340 µg/√Hz for the x- and y-axes and 470 µg/√Hz
for the z-axis.
10k
X-AXIS
Y-AXIS
Z-AXIS
1k
TION (µg)
100
ALLAN DEVI
10
0.01 0.1 1 10 100 1k 10k
AVERAGING PERIOD, (s)
Figure 34. Root Allan Deviation
130
120
110
100
90
X-AXIS
Y-AXIS
Z-AXIS
08791-251
80
PERCENTAGE OF NORMALIZED NO ISE (%)
70
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
SUPPLY VOLTAGE, V
(V)
S
Figure 35. Normalized Noise vs. Supply Voltage, V
08791-252
S
Rev. 0 | Page 28 of 32
Page 29
ADXL312
A
AXES OF ACCELERATION SENSITIVITY
Z
A
Y
A
X
08791-042
Figure 36. Axes of Acceleration Sensitivity (Corresponding Output Voltage Increases When Accelerated Along the Sensitive Axis)
X
= +1g
OUT
Y
= 0g
OUT
Z
= 0g
OUT
TOP
GRAVITY
X
X
= 0g
OUT
Y
= –1g
OUT
Z
= 0g
OUT
TOP
TOP
X
= –1g
OUT
Y
= 0g
OUT
Z
= 0g
OUT
TOP
= 0g
OUT
Y
= +1g
OUT
Z
= 0g
OUT
X
= 0g
OUT
Y
= 0g
OUT
Z
= +1g
OUT
X
= 0g
OUT
Y
= 0g
OUT
Z
= –1g
OUT
08791-043
Figure 37. Output Response vs. Orientation to Gravity
Rev. 0 | Page 29 of 32
Page 30
ADXL312
A
E
SOLDER PROFILE
TUR
TEMPER
SUPPLIER TP ≥ T
SUPPLIER
T
P
MAXIMUM RAM P UP RATE = 3°C/s
MAXIMUM RAMP DOWN RATE = 6°C/s
T
L
T
T
SMAX
SMIN
PREHEATAREA
C
T
C
TC –5°C
t
P
t
S
USER TP ≤ T
USER
t
P
t
L
C
t
P
–5°C
T
C
25
Table 23: Recommended Soldering Profile
TIME 25°C TO PEAK
TIME
Figure 38: Recommended Soldering Profile
1, 2
08791-038
Condition
Profile Feature
Sn63/Pb37 Pb-Free
Average Ramp Rate (TL to TP) 3°C/second maximum
Preheat
Minimum Temperature (T
Maximum Temperature (T
Time (T
T
to TL
SMAX
SMIN
to T
) (tS) 60 to 120 seconds 60 to 180 seconds
SMAX
) 100°C 150°C
SMIN
) 150°C 200°C
SMAX
Ramp-Up Rate 3°C/second
Time Maintained Above Liquidous (TL)
Liquidous Temperature (TL) 183°C 217°C
Time (tL) 60 to 150 seconds 60 to 150 seconds
Peak Temperature (TP) 240°C + 0°C/−5°C 260°C + 0°C/−5°C
Time Within 5°C of Actual Peak Temperature (tP) 10 to 30 seconds 20 to 40 seconds
Ramp-Down Rate 6°C/second maximum
Time 25°C to Peak Temperature 6 minutes maximum 8 minutes maximum
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. 0 | Page 30 of 32
Page 31
ADXL312
OUTLINE DIMENSIONS
PIN 1
INDICATOR
5.10
5.00 SQ
4.90
0.50
BSC
24
0.30
0.25
0.18
25
EXPOSED
PAD
N
I
1
32
P
R
O
T
N
D
C
I
A
I
1
3.70
3.60 SQ
3.50
1.55
1.45
1.35
SEATING
PLANE
0.05
17
BOTTOM VIEWTOP VIEW
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
0.45
0.40
0.35
0.05 MAX
0.02 NOM
COPLANARITY
0.20 REF
COMPLIANT TO JEDEC STANDARDS MO-254-LJJD.
Figure 39. 32-Lead Lead Frame Chip Scale Package [LFCSP_LQ]
5 mm × 5 mm Body, Thick Quad
(CP-32-17)
Dimensions shown in millimeters
5.34 mm
0.57 mm
3.60 mm
8
916
0.30 mm
0.20 MIN
12-03-2010-B
0.30 mm
0.50 mm
0.30 mm
Figure 40. Sample Solder Pad Layout (Land Pattern)
Rev. 0 | Page 31 of 32
08791-038
Page 32
ADXL312
ORDERING GUIDE
1, 2
Model
ADXL312WACPZ
Measurement
Range
±1.5 g, ±3 g, ±6 g,
±12 g
ADXL312WACPZ-RL
±1.5 g, ±3 g, ±6 g,
±12 g
ADXL312ACPZ
±1.5 g, ±3 g, ±6 g,
±12 g
ADXL312ACPZ-RL
±1.5 g, ±3 g, ±6 g,
±12 g
EVAL-ADXL312Z Evaluation Board
EVAL-ADXL312Z-M Evaluation Board
EVAL-ADXL312Z-S Evaluation Board
1
Z = RoHS Compliant Part
2
W = Qualified for Automotive Applications
AUTOMOTIVE PRODUCTS
The ADXL312W models are available with controlled manufacturing to support the quality and reliability requirements of automotive
applications. Note that these automotive models may have specifications that differ from the commercial models; therefore, designers
should review the Specifications section of this data sheet carefully. Only the automotive grade products shown are available for use in
automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to
obtain the specific Automotive Reliability reports for these models.
I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).
Specified
Voltage (V)
Te mp e ra tu r e
Range Package Description
3.3 −40°C to +105°C
3.3 −40°C to +105°C
3.3 −40°C to +105°C
3.3 −40°C to +105°C
32-Lead Lead Frame Chip Scale Package
[LFCSP_LQ]
32-Lead Lead Frame Chip Scale Package
[LFCSP_LQ]
32-Lead Lead Frame Chip Scale Package
[LFCSP_LQ]
32-Lead Lead Frame Chip Scale Package
[LFCSP_LQ]
Package
Option
CP-32-17
CP-32-17
CP-32-17
CP-32-17
©2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08791-0-12/10(0)
Rev. 0 | Page 32 of 32
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