3-Axis, ±1.5 g/±3 g/±6 g/±12 g
Digital Accelerometer
Data Sheet ADXL312
Rev. A Document Feedback
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FEATURES
Ultralow power: as low as 57 μA in measurement mode and
0.1 μA in standby mode at VS = 3.3 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 ±12 g (maintaining 2.9 mg/LSB
scale factor in all g ranges)
Embedded 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 I2C digital interfaces
Flexible interrupt modes mappable to either interrupt pin
Measurement ranges selectable via serial command
Bandwidth selectable via serial command
Wide temperature range (−40 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)
GENERAL DESCRIPTION
The ADXL3121 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 serial port interface (SPI) (3- or 4-wire)
or I2C digital interface.
The ADXL312 is well suited for car alarm or black box applica-
tions. 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 facili-
tates 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.
FUNCTIONAL BLOCK DIAGRAM
3-AXIS
SENSOR
SENSE
ELECTRONICS DIGITAL
FILTER
ADXL312 POWER
MANAGEMENT
CONTROL
AND
INTERRUPT
LOGIC
SERIAL I/O
INT1
V
S
V
DD I/O
INT2
SDA/SDI/SDIO
SDO/ALT
ADDRESS
SCL/SCLK
GND
ADC
32 LEVEL
FIFO
CS
08791-001
Figure 1. ADXL312 Simplified Block Diagram
1 Protected by U.S. Patent 8,156,264B2.
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DOCUMENTATION
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•ADXL312: 3-Axis, ±1.5
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/±3
g
/±6
g
/±12
g
Digital
Accelerometer Data Sheet
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ADXL312 Data Sheet
Rev. A | Page 2 of 32
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
7/15—Rev. 0 to Rev. A
Changes to Features Section............................................................ 1
Changes to Pin 22 Description, Table 4 ......................................... 6
Changes to Serial Communications Section, SPI Section,
Figure 21, and Figure 22 ................................................................ 12
Added Serial Port I/O Default States Section ............................. 12
Added Preventing Bus Traffic Errors Section and Figure 23;
Renumbered Sequentially ............................................................. 13
Changes to FIFO Section ............................................................... 18
Changes to Figure 41 ...................................................................... 31
12/10—Revision 0: Initial Version
Data Sheet ADXL312
Rev. A | Page 3 of 32
SPECIFICATIONS
TA = −40°C to +105°C, VS = VDD I/O = 3.3 V, acceleration = 0 g, unless otherwise noted.
Table 1. Specifications1
Parameter Test Conditions/Comments Min Typ Max Unit
SENSOR INPUT Each axis
Measurement Range User selectable ±1.5, 3, 6, 12 g
Nonlinearity Percentage of full scale ±0.5 %
Inter-Axis Alignment Error ±0.1 Degrees
Cross-Axis Sensitivity2 ±1 %
OUTPUT RESOLUTION Each axis
All g Ranges 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
OUT
, Y
OUT
, Z
OUT
±1.5 g, 10-bit or full resolution 2.6 2.9 3.2 mg/LSB
Scale Factor at X
OUT
, Y
OUT
, Z
OUT
±3 g, 10-bit resolution 5.2 5.8 6.4 mg/LSB
Scale Factor at X
OUT
, Y
OUT
, Z
OUT
±6 g, 10-bit resolution 10.4 11.6 12.8 mg/LSB
Scale Factor at X
OUT
, Y
OUT
, Z
OUT
±12 g, 10-bit resolution 20.9 23.2 25.5 mg/LSB
Sensitivity at XOUT, YOUT, ZOUT
±1.5
g
, 10-bit or full resolution
312
345
385
LSB/
g
Sensitivity at X
OUT
, Y
OUT
, Z
OUT
±3 g, 10-bit resolution 156 172 192 LSB/g
Sensitivity at X
OUT
, Y
OUT
, Z
OUT
±6 g, 10-bit resolution 78 86 96 LSB/g
Sensitivity at X
OUT
, Y
OUT
, Z
OUT
±12 g, 10-bit resolution 39 43 48 LSB/g
Sensitivity Change Due to Temperature ±0.01 %/°C
0 g BIAS LEVEL Each axis
Initial 0 g Output T = 25°C, X
OUT
, Y
OUT
−150 +150 mg
Initial 0 g Output T = 25°C, Z
OUT
−250 +250 mg
0 g Output over Temperature −40°C < T < 105°C, X
OUT
, Y
OUT
, Z
OUT
−250 +250 mg
0 g Offset Tempco X
OUT
, Y
OUT
±0.8 mg/°C
0 g Offset Tempco Z
OUT
±1.5 mg/°C
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 ≤ V
S
≤ 3.6
Output Change in X-Axis
0.20
2.10
g
Output Change in Y-Axis −2.10 −0.20 g
Output Change in Z-Axis 0.30 3.40 g
POWER SUPPLY
Operating Voltage Range (V
S
) 2.0 3.6 V
Interface Voltage Range (V
DD I/O
) 1.7 V
S
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
ADXL312 Data Sheet
Rev. A | Page 4 of 32
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).
Data Sheet ADXL312
Rev. A | Page 5 of 32
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Acceleration
Any Axis, Unpowered 10,000 g
Any Axis, Powered 10,000 g
V
S
−0.3 V to 3.9 V
V
DD I/O
−0.3 V to 3.9 V
All Other Pins −0.3 V to VDD I/O + 0.3 V or
3.9 V, whichever is less
Output Short-Circuit Duration
(Any Pin to Ground)
Indefinite
Temperature Range
Powered −40°C to +125°C
Storage −40°C to +125°C
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
THERMAL RESISTANCE
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 θ
JA
θ
JC
Unit
32-Lead LFCSP Package 27.27 30 °C/W
ESD CAUTION
ADXL312 Data Sheet
Rev. A | Page 6 of 32
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
NOTES
1. NC = NO CO NNE C T. DO NOT CONNECT TO THIS PIN.
2. THE EXPOSED PAD MUST BE SOL DE RE D TO THE GROUND P LANE.
24 SDA/SDI/SDIO
23 SDO/ALTADDRESS
22 RESERVED
21 INT2
20 INT1
19 NC
18 NC
17 NC
1
2
3
4
5
6
7
8
GND
RESERVED
GND
GND
VS
CS
RESERVED
NC
9
10
11
12
13
14
15
16
NC
NC
NC
NC
NC
NC
NC
NC
32
31
30
29
28
27
26
25
NC
VDD I/O
NC
NC
NC
NC
SCL/SCLK
NC
TOP VIEW
(No t t o Scal e)
ADXL312
08791-002
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 V
S
or left open.
3
GND
This pin must be connected to ground.
4 GND This pin must be connected to ground.
5 V
S
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.
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
DD I/O
Digital Interface Supply Voltage.
32 NC No Connect.
EP
The exposed pad must be soldered to the ground plane.
Data Sheet ADXL312
Rev. A | Page 7 of 32
TYPICAL PERFORMANCE CHARACTERISTICS
N > 1000, unless otherwise noted.
0
5
10
15
20
25
30
35
40
–150 –120 –60 –30–90 06030 90 120 150
ZERO g OFFSET (mg)
PERCENT OF POPULATION (%)
08791-003
Figure 3. X-Axis Zero-g Bias. 25°C, VS = VDD I/O = 3.3 V
0
5
10
15
20
25
30
35
–150 –120 –60 –30–90 06030 90 120 150
ZERO g OFFSET (mg)
PERCENT OF POPULATION (%)
08791-004
Figure 4. Y Axis Zero-g Bias, 25°C, VS = VDD I/O = 3.3 V
0
5
10
15
20
25
30
35
40
45
50
–250 –200 –100 –50–150 010050 150 200 250
ZERO g OFFSET (mg)
PERCENT OF POPULATION (%)
08791-005
Figure 5. Z Axis Zero-g Bias, 25°C, VS = VDD I/O = 3.3 V
0
5
10
15
20
25
30
35
40
–3.0
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
2.0
3.0
1.5
2.5
ZERO g T EMPERATURE COEFFICIENT (mg/°C)
PERCENT OF POPULATION (%)
08791-006
Figure 6. X-Axis Zero-g Bias Drift, VS = VDD I/O = 3.3 V
0
5
10
15
20
25
30
35
40
–3.0
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
2.0
3.0
1.5
2.5
ZERO g T EMPERATURE COEFFICIENT (mg/°C)
PERCENT OF POPULATION (%)
08791-007
Figure 7. Y-Axis Zero-g Bias Drift, VS = VDD I/O = 3.3 V
0
5
10
15
20
25
–3.0
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
2.0
3.0
1.5
2.5
ZERO g T EMPERATURE COEFFICIENT (mg/°C)
PERCENT OF POPULATION (%)
08791-008
Figure 8. Z-Axis Zero-g Bias Drift, VS = VDD I/O = 3.3 V
ADXL312 Data Sheet
Rev. A | Page 8 of 32
0
10
20
40
60
30
50
70
312
318
324
330
336
342
348
354
360
372
384
366
378
SENSITIVITY (LSB/g)
PERCENT OF POPULATION (%)
08791-009
Figure 9. X-Axis Sensitivity, VS = VDD I/O = 3.3 V, 25°C
0
10
20
40
60
30
50
70
312
318
324
330
336
342
348
354
360
372
384
366
378
SENSITIVITY (LSB/g)
PERCENT OF POPULATION (%)
08791-010
Figure 10. Y-Axis Sensitivity, VS = VDD I/O = 3.3 V, 25°C
0
10
20
40
60
30
50
70
312
318
324
330
336
342
348
354
360
372
384
366
378
SENSITIVITY (LSB/g)
PERCENT OF POPULATION (%)
08791-011
Figure 11. Z-Axis Sensitivity, VS = VDD I/O = 3.3 V, 25°C
0
5
10
20
15
25
30
–0.030
–0.025
–0.020
–0.015
–0.010
–0.005
0
0.005
0.010
0.020
0.030
0.015
0.025
SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)
PERCENT OF POPULATION (%)
08791-012
Figure 12. X-Axis Sensitivity Temperature Coefficient, VS = VDD I/O = 3.3 V
0
5
10
20
15
25
35
30
–0.030
–0.025
–0.020
–0.015
–0.010
–0.005
0
0.005
0.010
0.020
0.030
0.015
0.025
SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)
PERCENT OF POPULATION (%)
08791-013
Figure 13. Y-Axis Sensitivity Temperature Coefficient, VS = VDD I/O = 3.3 V
0
5
10
20
15
25
35
30
–0.030
–0.025
–0.020
–0.015
–0.010
–0.005
0
0.005
0.010
0.020
0.030
0.015
0.025
SENSITIVITY TEMPERATURE COEFFICIENT (%/°C)
PERCENT OF POPULATION (%)
08791-014
Figure 14. Z-Axis Sensitivity Temperature Coefficient, VS = VDD I/O = 3.3 V
Data Sheet ADXL312
Rev. A | Page 9 of 32
0
10
20
40
30
50
80
70
60
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SELF-T EST RESPONSE (g)
PERCENT OF POPULATION (%)
08791-015
Figure 15. X-Axis Self-Test Delta, VS = VDD I/O = 3.3 V, 25°C
0
10
20
40
30
50
70
60
–2.1
–1.9
–1.7
–1.5
–1.3
–1.1
–0.9
–0.7
–0.5
–0.3
SELF-T EST RESPONSE (g)
PERCENT OF POPULATION (%)
08791-016
Figure 16. Y-Axis Self-Test Delta, VS = VDD I/O = 3.3 V, 25°C
0
10
20
40
30
50
80
70
60
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.33.0
SELF-T EST RESPONSE (g)
PERCENT OF POPULATION (%)
08791-017
Figure 17. Z-Axis Self-Test Delta, VS = VDD I/O = 3.3 V, 25°C
0
10
20
40
30
50
80
70
60
30
50
70
90
110
130
150
170
190
210
230
250
270
290
310
CURRENT (nA)
PERCENT OF POPULATION (%)
08791-018
Figure 18. Standby Mode Current Consumption, VS = VDD I/O = 3.3 V, 25°C
0
5
10
20
15
25
35
30
100
120
140
160
180
200
220
240
260
280
300
CURRENT CONSUM P TION (µA)
PERCENT OF POPULATION (%)
08791-019
Figure 19. Current Consumption, Measurement Mode, Data Rate = 100 Hz,
VS = VDD I/O = 3.3 V, 25°C
0
50
100
150
200
2.0 2.4 2.8 3.2 3.6
SUPPLY
VOLTAGE (V)
SUPPLY CURRENT ( µA)
08791-233
Figure 20. Supply Current vs. Supply Voltage, VS at 25°C
ADXL312 Data Sheet
Rev. A | Page 10 of 32
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. Phase-
sensitive demodulation is used to determine the magnitude and
polarity of the acceleration.
POWER SEQUENCING
Power can be applied to VS or VDD I/O in any sequence without
damaging the ADXL312. All possible power-on modes are
summarized in Table 5. The interface voltage level is set with
the interface supply voltage, VDD I/O, which must be present to
ensure that the ADXL312 does not create a conflict on the
communication bus. For single-supply operation, VDD I/O can be
the same as the main supply, VS. In a dual-supply application,
however, VDD I/O can differ from VS to accommodate the desired
interface voltage, as long as VS is greater than or equal to VDD I/O.
After VS is applied, the device enters standby mode, where power
consumption is minimized and the device waits for VDD I/O to be
applied and for the command to enter measurement mode to be
received. (This command can be initiated by setting the measure
bit in the POWER_CTL register (Address 0x2D).) In addition, any
register can be written to or read from to configure the part while
the device is in standby mode. It is recommended to configure the
device in standby mode and then to enable measurement mode.
Clearing the measure bit returns the device to the standby mode.
Table 5. Power Sequencing
Condition V
S
V
DD I/O
Description
Power Off Off Off The device is completely off, but
there is a potential for a
communication bus conflict.
Bus Disabled On Off The device is on in standby mode,
but communication is unavailable
and creates a conflict on the
communication bus. The duration
of this state should be minimized
during power-up to prevent a
conflict.
Bus Enabled Off On No functions are available, but
the device will not create a conflict
on the communication bus.
Standby or
Measurement
On On 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 Table 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 Table 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 Table 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 Table 7 be used in
low power mode. The current consumption values shown in
Table 6 and Table 7 are for a VS of 3.3 V.
Data Sheet ADXL312
Rev. A | Page 11 of 32
Table 6. Current Consumption vs. Data Rate
(TA = 25°C, VS = VDD I/O = 3.3 V)
Output Data
Rate (Hz) Bandwidth (Hz) Rate Code I
DD
(µA)
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
Table 7. Current Draw vs. Data Rate, Low Power Mode
(TA = 25°C, VS = VDD I/O = 3.3 V)
Output Data
Rate (Hz) Bandwidth (Hz) Rate Code I
DD
(µA)
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
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 VS of 3.3 V.
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.
ADXL312 Data Sheet
Rev. A | Page 12 of 32
SERIAL COMMUNICATIONS
The ADXL312 can communicate via I2C and SPI digital
communications interfaces. In both cases, the ADXL312 operates
as a slave. If I2C is the desired interface for the application, tie
the CS pin directly to VDD I/O as shown in Figure 27. If SPI is the
desired interface for the application, drive the CS pin with an
external controller, as demonstrated in Figure 21 and Figure 22.
Because the I2C interface is enabled any time the CS pin is brought
up to VDD I/O, there is a potential for bus conflicts to occur when the
ADXL312 is implemented into a SPI network. Refer to the
Preventing Bus Traffic Errors section for information on how to
avoid such conditions. In both SPI and I2C modes of operation,
ignore data transmitted from the ADXL312 to the master device
during writes to the ADXL312.
Note that throughout this section, multifunction pins, such as
SDA/SDI/SDIO, are referred to either by the entire pin name or
by a single function of the pin, for example, SDA, when only
that function is relevant.
SERIAL PORT I/O DEFAULT STATES
Ensure that all serial port I/Os are in a defined state and that no
pin is allowed to float when not in use. This is applicable to all
serial port I/Os, regardless of SPI or I2C operation.
For I2C applications, always tie the CS pin high to VDD I/O.
Connect the SCL and SDA pins to an external controller, with
pull-up resistors implemented according to the UM10204 I2C-
Bus Specification and User Manual, Rev. 03—19 June 2007,
available from NXP Semiconductor. The ALT ADDRESS pin
must be tied to either VDD I/O or ground, thereby selecting the
desired I2C address for the ADXL312.
If SPI is the intended communications interface, drive the CS
pin with an external controller, as shown in Figure 21 and
Figure 22. When communications with the ADXL312 are
suspended (CS = VDD I/O), ensure that the SCLK, SDI/SDIO, and
SDO pins are not floating.
For either SPI or I2C operation, not taking these precautions may
result in an inability to communicate with the device or excessive
current consumption.
SPI
For the 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, bring the CS pin high before changing
the clock polarity and phase. When using 3-wire SPI, pull the
SDO pin up to VDD I/O or down to ground via a 10 kΩ resistor, as
shown in Figure 21.
CS is the serial port enable line and is controlled by the SPI master.
This line must go low at the start of a transmission and high at
the end of a transmission, as shown in Figure 24. SCLK is the
serial port clock and is supplied by the SPI master. SDI and
SDO are the serial data input and output, respectively.
08791-044
ADXL312
PROCESSOR
CS
SDIO
SDO
SCLK
D_OUT
D_IN/OUT
D_OUT
R
PD
Figure 21. 3-Wire SPI Connection Diagram
08791-045
ADXL312
PROCESSOR
CS
SDI
SDO
SCLK
D_OUT
D_OUT
D_IN
D_OUT
Figure 22. 4-Wire SPI Connection Diagram
To read or write multiple bytes in a single transmission, the
multiple-byte bit, located after the R/W bit in the first byte transfer
(MB in Figure 24 to Figure 26), must be set. After the register
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 CS is deasserted. To perform reads
or writes on different nonsequential registers, CS must be
deasserted between transmissions, and the new register must be
addressed separately.
The timing diagram for 3-wire SPI reads or writes is shown in
Figure 26. The 4-wire equivalents for SPI writes and reads are
shown in Figure 24 and Figure 25, respectively. For correct opera-
tion of the device, 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.
Data Sheet ADXL312
Rev. A | Page 13 of 32
Preventing Bus Traffic Errors
The ADXL312 CS pin initiates SPI transactions and enables I2C
mode. When the ADXL312 is used on a SPI bus with multiple
devices, its CS pin is held high while the master communicates
with the other devices. There may be conditions where a SPI
command transmitted to another device looks like a valid I2C
command. In this case, the ADXL312 interprets this as an
attempt to communicate in I2C mode and may interfere with
other bus traffic. Unless bus traffic can be adequately controlled
to ensure such a condition never occurs, it is recommended to
add a logic gate in front of the SDI pin, as shown in Figure 23.
This OR gate holds the SDA line high when CS is high to
prevent bus traffic at the ADXL312 from appearing as an I2C
start command.
08791-046
ADXL312
PROCESSOR
CS
SDI
SDO
SCLK
D_OUT
D_OUT
D_IN
D_OUT
Figure 23. Recommended SPI Connection Diagram when Using Multiple SPI
Devices on a Single Bus
Table 8. SPI Digital Input/Output
Limit1
Parameter Test Conditions Min Max Unit
Digital Input
Low Level Input Voltage (V
IL
) 0.3 × V
DD I/O
V
High Level Input Voltage (V
IH
) 0.7 × V
DD I/O
V
Low Level Input Current (I
IL
) V
IN
= V
DD I/O
0.1 µA
High Level Input Current (I
IH
) V
IN
= 0 V −0.1 µA
Digital Output
Low Level Output Voltage (V
OL
) I
OL
= 10 mA 0.2 × V
DD I/O
V
High Level Output Voltage (V
OH
) I
OH
= −4 mA 0.8 × V
DD I/O
V
Low Level Output Current (I
OL
) V
OL
= V
OL, max
10 mA
High Level Output Current (I
OH
) V
OH
= V
OH, min
−4 mA
Pin Capacitance f
IN
= 1 MHz, V
IN
= 2.5 V 8 pF
1 Limits based on characterization results, not production tested.
Table 9. SPI Timing (TA = 25°C, VS = VDD I/O = 3.3 V)1
Limit2, 3
Parameter
Min
Max
Unit
Description
f
SCLK
5 MHz SPI clock frequency.
tSCLK
200
ns
1/(SPI clock frequency) mark-space ratio for the SCLK input is 40/60 to 60/40.
tDELAY 5 ns CS falling edge to SCLK falling edge .
tQUIET 5 ns SCLK rising edge to CS rising edge.
tDIS 10 ns CS rising edge to SDO disabled.
t
CS,DIS
150 ns CS deassertion between SPI communications.
t
S
0.3 × t
SCLK
ns SCLK low pulse width (space).
t
M
0.3 × t
SCLK
ns SCLK high pulse width (mark).
t
SETUP
5 ns SDI valid before SCLK rising edge.
t
HOLD
5 ns SDI valid after SCLK rising edge.
t
SDO
40 ns SCLK falling edge to SDO/SDIO output transition.
t
R
4 20 ns SDO/SDIO output high to output low transition.
tF4
20
ns
SDO/SDIO output low to output high transition.
1 The CS, SCLK, SDI, and SDO pins are not internally pulled up or down; they must be driven for proper operation.
2 Limits based on characterization results, characterized with fSCLK = 5 MHz and bus load capacitance of 100 pF; not production tested.
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.
ADXL312 Data Sheet
Rev. A | Page 14 of 32
t
DELAY
t
SETUP
t
HOLD
t
SDO
t
R
,
t
F
XXX
WMB A5 A0 D7 D0
XX X
ADDRESS BITS DATA BITS
t
SCLK
t
M
t
S
t
QUIET
t
DIS
t
CS,DIS
S
CL
K
SDI
SDO
CS
08791-129
Figure 24. SPI 4-Wire Write
CS
XXX
RMBA5 A0
D7 D0X
XX
ADDRESS BITS
DATA BITS
t
DIS
SCL
K
SDI
SDO
t
QUIET
t
SDO
t
SETUP
t
DELAY
t
SCLK
t
M
t
S
t
R
,
t
F
t
HOLD
t
CS,DIS
08791-130
Figure 25. SPI 4-Wire Read
CS
t
DELAY
t
SETUP
t
HOLD
t
SDO
R/W MB A5 A0 D7 D0
ADDRESS BITS DATA BITS
t
SCLK
t
M
t
S
t
QUIET
SCLK
SDIO
SDO
NOTES
1. t
SDO
IS ONLY PRESENT DURING READS.
t
R
,t
F
t
CS,DIS
08791-131
Figure 26. SPI 3-Wire Read/Write
Data Sheet ADXL312
Rev. A | Page 15 of 32
I2C
With CS tied high to VDD I/O, the ADXL312 is in I2C mode,
requiring a simple 2-wire connection as shown in Figure 27.
The ADXL312 conforms to the UM10204 I2C-Bus Specification
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 Table 10 and
Table 11 are met. Single- or multiple-byte reads/writes are
supported, as shown in Figure 28. With the ALT ADDRESS pin
high, the 7-bit I2C address for the device is 0x1D, followed by the
R/W bit. This translates to 0x3A for a write and 0x3B for a read. An
alternate I2C address of 0x53 (followed by the R/W bit) can be
chosen by grounding the ALT ADDRESS pin (Pin 7). This
translates to 0xA6 for a write and 0xA7 for a read.
PROCESSOR
D IN/ OUT
D OUT
RP
VDD I/O
RP
ADXL312
CS
SDA
ALT ADDRESS
SCL
08791-032
Figure 27. I2C Connection Diagram (Address 0x53)
If other devices are connected to the same I2C bus, the nominal
operating voltage level of these other devices cannot exceed VDD I/O
by more than 0.3 V. External pull-up resistors, RP, are necessary
for proper I2C operation. Refer to the UM10204 I2C-Bus
Specification and User Manual, Rev. 03—19 June 2007, when
selecting pull-up resistor values to ensure proper operation.
Table 10. I2C Digital Input/Output
Limit1
Parameter Test Conditions Min Max Unit
Digital Input
Low Level Input Voltage (V
IL
) 0.3 × V
DD I/O
V
High Level Input Voltage (V
IH
) 0.7 × V
DD I/O
V
Low Level Input Current (I
IL
) V
IN
= V
DD I/O
0.1 µA
High Level Input Current (I
IH
) V
IN
= 0 V −0.1 µA
Digital Output
Low Level Output Voltage (V
OL
) V
DD I/O
< 2 V, I
OL
= 3 mA 0.2 × V
DD I/O
V
V
DD I/O
≥ 2 V, I
OL
= 3 mA 400 mV
Low Level Output Current (I
OL
) V
OL
= V
OL, max
3 mA
Pin Capacitance f
IN
= 1 MHz, V
IN
= 2.5 V 8 pF
1 Limits based on characterization results; not production tested.
NOTES
1. THIS START IS EITHER A RESTART OR A STOP FOLLOWED BY A START.
2. T HE S HADE D ARE AS RE P RE S E NT W HE N THE DEV ICE IS L ISTENI NG.
08791-033
MASTER START SLAVE ADDRESS + WRIT E REGIS TER ADDRE SS
SLAVE ACK ACK ACK
MASTER START SLAVE ADDRESS + WRIT E REGIS TER ADDRE SS
SLAVE ACK ACK ACK ACK
MASTER START SLAVE ADDRESS + WRIT E REGIS TER ADDRE SS STOP
SLAVE ACK ACK
MASTER START
START
1
START
1
SLAVE ADDRESS + WRI T E REGIS TE R ADDRESS NACK STOP
SLAVE ACK ACK DATA
STOP
ACK
SINGLE-BYTE W RI T E
MULTIPLE- BYTE WRI TE
DATA
DATA
MULTIPLE-BYTE READ
SLAVE ADDRESS + READ
SLAVE ADDRESS + READ
ACK
DATA
DATA
DATA
STOP
NACK
ACK
SINGLE-BYTE READ
Figure 28. I2C Device Addressing
ADXL312 Data Sheet
Rev. A | Page 16 of 32
Table 11. I2C Timing (TA = 25°C, VS = VDD I/O = 3.3 V)
Limit1, 2
Parameter Min Max Unit Description
f
SCL
400 kHz SCL clock frequency
t
1
2.5 µs SCL cycle time
t
2
0.6 µs t
HIGH
, SCL high time
t
3
1.3 µs t
LOW
, SCL low time
t
4
0.6 µs t
HD, STA
, start/repeated start condition hold time
t
5
100 ns t
SU, DAT
, data setup time
t
6
3, 4, 5, 6 0 0.9 µs t
HD, DAT
, data hold time
t
7
0.6 µs t
SU, STA
, setup time for repeated start
t
8
0.6 µs t
SU, STO
, stop condition setup time
t
9
1.3 µs t
BUF
, bus-free time between a stop condition and a start condition
t
10
300 ns t
R
, rise time of both SCL and SDA when receiving
0 ns t
R
, 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
b7
ns t
F
, fall time of both SCL and SDA when transmitting or receiving
C
b
400 pF Capacitive load for each bus line
1 Limits based on characterization results, with fSCL = 400 kHz and a 3 mA sink current; not production tested.
2 All values referred to the VIH and the VIL levels given in Table 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 VIH(min) of the SCL signal) to bridge the
undefined region of the falling edge of SCL.
5 The maximum t6 value must be met only if the device does not stretch the low period (t3) of the SCL signal.
6 The maximum value for t6 is a function of the clock low time (t3), the clock rise time (t10), and the minimum data setup time (t5(min)). This value is calculated as
t6(max) = t3 − t10 − t5(min).
7 Cb is the total capacitance of one bus line in picofarads.
SDA
t9
SCL
t3t10 t11 t4
t4t6t2t5t7t1t8
START
CONDITION REPEATED
START
CONDITION
STOP
CONDITION
08791-034
Figure 29. I2C Timing Diagram
Data Sheet ADXL312
Rev. A | Page 17 of 32
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 Table 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 con-
figuration of an interrupt, it is recommended that the interrupt be
disabled first, by clearing the bit corresponding to that function in
the INT_ENABLE register, and then the function be reconfigured
before enabling the interrupt again. Configuration of the functions
while the interrupts are disabled helps to prevent the accidental
generation of an interrupt before desired.
The interrupt functions are latched and cleared by either reading
the data registers (Address 0x32 to Address 0x37) until the inter-
rupt 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.
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.
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 × VDD I/O V
High Level Output Voltage (VOH) IOH = −150 μA 0.8 × VDD I/O V
Low Level Output Current (IOL) VOL = VOL, max 300 μA
High Level Output Current (IOH) VOH = VOH, min −150 μA
Pin Capacitance fIN = 1 MHz, VIN = 2.5 V 8 pF
Rise/Fall Time
Rise Time (tR)2 C
LOAD = 150 pF 210 ns
Fall Time (tF)3 C
LOAD = 150 pF 150 ns
1 Limits based on characterization results, not production tested.
2 Rise time is measured as the transition time from VOL, max to VOH, min of the interrupt pin.
3 Fall time is measured as the transition time from VOH, min to VOL, max of the interrupt pin.
ADXL312 Data Sheet
Rev. A | Page 18 of 32
FIFO
The ADXL312 contains technology for an embedded memory
management system with 32-level FIFO that can be used to
minimize host processor burden. This buffer has four modes:
bypass, FIFO, stream, and trigger (see Table 21). 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 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 and holds the latest 32 samples
from measurements of the x-, y-, and z-axes, discarding older
data as new data arrives. The watermark interrupt continues
occurring until the number of samples in FIFO is less than the
value stored in the samples bits of the FIFO_CTL register.
Trigger Mode
In trigger mode, FIFO accumulates samples, holding the latest
32 samples from measurements of the x-, y-, and z-axes. After
a trigger event occurs and an interrupt is sent to the INT1 or
INT2 pin (determined by the trigger bit in the FIFO_CTL register),
FIFO keeps the last n samples (where n is the value specified by
the samples bits in the FIFO_CTL register) and then operates in
FIFO mode, collecting new samples only when FIFO is not full.
A delay of at least 5 μs should be present between the trigger event
occurring and the start of reading data from the FIFO to allow
the FIFO to discard and retain the necessary samples. Additional
trigger events cannot be recognized until the trigger mode is
reset. To reset the trigger mode, set the device to bypass mode
and then set the device back to trigger mode. Note that the FIFO
data should be read first because placing the device into bypass
mode clears FIFO.
Retrieving Data from FIFO
The FIFO data is read through the DATAX, DATAY, and DATAZ
registers (Address 0x32 to Address 0x37). When the FIFO is in
FIFO, stream, or trigger mode, reads to the DATAX, DATAY,
and DATAZ registers read data stored in the FIFO. Each time
data is read from the FIFO, the oldest x-, y-, and z-axes data 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 μs between the
end of reading the data registers and the start of a new read of
the FIFO or a read of the FIFO_STATUS register (Address 0x39).
The end of reading a data register is signified by the transition
from Register 0x37 to Register 0x38 or by the CS pin going high.
For SPI operation at 1.6 MHz or less, the register addressing
portion of the transmission is a sufficient delay to ensure that
the FIFO has completely popped. For SPI operation greater than
1.6 MHz, it is necessary to deassert the CS pin to ensure a total
delay of 5 μs; otherwise, the delay will not be sufficient. The total
delay necessary for 5 MHz operation is at most 3.4 μs. This is
not a concern when using I2C mode because the communication
rate is low enough to ensure a sufficient delay between FIFO reads.
Data Sheet ADXL312
Rev. A | Page 19 of 32
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 VS2, the output change varies with VS. This
effect is shown in Figure 30. The scale factors shown in Table 13
can be used to adjust the expected self-test output limits for
different supply voltages, VS. The self-test feature of the
ADXL312 also exhibits a bimodal behavior. However, the limits
shown in Table 1 and Table 14 to Table 17 are valid for both
potential self-test 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
0
2
4
6
2.0 2.5 3.3 3.6
VS (V)
SELF-TEST SHIFT LIMIT (g)
X HIGH
X LO W
Y HIG H
Y LOW
Z HIGH
Z LOW
08791-242
Figure 30. Self-Test Output Change Limits vs. Supply Voltage
Table 13. Self-Test Output Scale Factors for Different Supply
Voltages, VS
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 (TA = 25°C, VS = VDD 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
(TA = 25°C, VS = VDD 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
(TA = 25°C, VS = VDD I/O = 2.5 V)
Axis Min Max Unit
X 16 181 LSB
Y −181 −16 LSB
Z 25 294 LSB
Table 17. Self-Test Output in LSB for ±12 g, 10-Bit
Resolution (TA = 25°C, VS = VDD I/O = 2.5 V)
Axis Min Max Unit
X 8 90 LSB
Y −90 −8 LSB
Z 12 147 LSB
ADXL312 Data Sheet
Rev. A | Page 20 of 32
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 R/W 00000000 X-axis offset.
0x1F 31 OFSY R/W 00000000 Y-axis offset.
0x20 32 OFSZ R/W 00000000 Z-axis offset.
0x21 33 Reserved Reserved. Do not access.
0x22 34 Reserved Reserved. Do not access.
0x23 35 Reserved Reserved. Do not access.
0x24
36
THRESH_ACT
R/
W
00000000
Activity threshold.
0x25 37 THRESH_INACT R/W 00000000 Inactivity threshold.
0x26 38 TIME_INACT R/W 00000000 Inactivity time.
0x27 39 ACT_INACT_CTL R/W 00000000 Axis enable control for activity and inactivity detection.
0x28 40 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 R/W 00001010 Data rate and power mode control.
0x2D 45 POWER_CTL R/W 00000000 Power-saving features control.
0x2E 46 INT_ENABLE R/W 00000000 Interrupt enable control.
0x2F
47
INT_MAP
R/
W
00000000
Interrupt mapping control.
0x30 48 INT_SOURCE R 00000010 Source of interrupts.
0x31 49 DATA_FORMAT R/W 00000000 Data format control.
0x32 50 DATAX0 R 00000000 X-Axis Data 0.
0x33 51 DATAX1 R 00000000 X-Axis Data 1.
0x34 52 DATAY0 R 00000000 Y-Axis Data 0.
0x35
53
DATAY1
R
00000000
Y-Axis Data 1.
0x36 54 DATAZ0 R 00000000 Z-Axis Data 0.
0x37 55 DATAZ1 R 00000000 Z-Axis Data 1.
0x38 56 FIFO_CTL R/W 00000000 FIFO control.
0x39 57 FIFO_STATUS R 00000000 FIFO status.
Data Sheet ADXL312
Rev. A | Page 21 of 32
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 inactiv-
ity 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 Table 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 communication
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,
ADXL312 Data Sheet
Rev. A | Page 22 of 32
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 measure-
ment mode with a subsequent write. This is done to ensure that
the device is properly biased if sleep mode is manually disabled;
otherwise, the first few samples of data after the AUTO_SLEEP
bit is cleared may have additional noise, especially if the device
was asleep when the bit was cleared.
Measure Bit
A setting of 0 in the measure bit places the part into standby mode,
and a setting of 1 places the part into measurement mode. The
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.
Wake-Up Bits
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.
Data Sheet ADXL312
Rev. A | Page 23 of 32
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 Table 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 Table 21.
Table 21. FIFO Modes
Setting
D7 D6 Mode Function
0 0 Bypass FIFO is bypassed.
0 1 FIFO FIFO collects up to 32 values and then
stops collecting data, collecting new data
only when FIFO is not full.
1 0 Stream FIFO holds the last 32 data values. When
FIFO is full, the oldest data is overwritten
with newer data.
1 1 Trigger When triggered by the trigger bit, FIFO
holds the last data samples before the
trigger event and then continues to collect
data until 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 Specifies how many FIFO entries are needed to
trigger a watermark interrupt.
Stream Specifies how many FIFO entries are needed to
trigger a watermark interrupt.
Trigger Specifies how many FIFO samples are retained in
the FIFO buffer before a trigger event.
ADXL312 Data Sheet
Rev. A | Page 24 of 32
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.
Data Sheet ADXL312
Rev. A | Page 25 of 32
APPLICATIONS INFORMATION
POWER SUPPLY DECOUPLING
A 1 μF tantalum capacitor (CS) at VS and a 0.1 μF ceramic capacitor
(CI/O) at VDD I/O placed close to the ADXL312 supply pins is
recommended to adequately decouple the accelerometer from
noise on the power supply. If additional decoupling is necessary,
a resistor or ferrite bead, no larger than 100 Ω, in series with VS
may be helpful. Additionally, increasing the bypass capacitance
on VS to a 10 μF tantalum capacitor in parallel with a 0.1 μF
ceramic capacitor may also improve noise.
Care should be taken to ensure that the connection from the
ADXL312 ground to the power supply ground has low impedance
because noise transmitted through ground has an effect similar
to noise transmitted through VS. It is recommended that VS and
VDD I/O be separate supplies to minimize digital clocking noise
on the VS supply. If this is not possible, additional filtering of
the supplies as previously mentioned may be necessary.
ADXL312
GND
INT1
INT2 CS
SCL/SCLK
SDO/AL T ADDRESS
SDA/SDI/SDIO 3-W IRE O R
4-WIRE SPI
OR I2C
INTERFACE
VS
VS
CS
VDD I/O
VDD I/O
CI/O
INTERRUPT
CONTROL
08791-035
Figure 31. Application Diagram
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 32, may result in large, apparent measurement errors due
to undampened PCB vibration. Locating the accelerometer near
a hard mounting point ensures that any PCB vibration at the
accelerometer is above the accelerometer’s mechanical sensor
resonant frequency and, therefore, effectively invisible to the
accelerometer. Multiple mounting points, close to the sensor,
and/or a thicker PCB also help to reduce the effect of system
resonance on the performance of the sensor.
MOUNTING POINTS
PCB
ACCELEROMETERS
08791-036
Figure 32. Incorrectly Placed Accelerometers
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.
ADXL312 Data Sheet
Rev. A | Page 26 of 32
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 recom-
mended 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, XST_OFF, YST_OFF, and ZST_OFF.
Next, self-test should be enabled by setting Bit D7 of the
DATA_FORMAT register (Address 0x31). The output needs
some time (about four samples) to settle 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
is recommended that the same number of samples be taken for
this average as was previously taken. These averaged values should
again be stored and labeled appropriately as the value with self-
test enabled, that is, XST_ON, YST_ON, and ZST_ON. Self-test can then
be disabled by clearing Bit D7 of the DATA_FORMAT register
(Address 0x31).
With the stored values for self-test enabled and disabled, the
self-test change is as follows:
XST = XST_ON − XST_OFF
YST = YST_ON − YST_OFF
ZST = ZST_ON − ZST_OFF
Because the measured output for each axis is expressed in LSBs,
XST, YST, and ZST are also expressed in LSBs. These values can be
converted to g’s of acceleration by multiplying each value by the
2.9 mg/LSB scale factor, if configured for full-resolution mode.
Additionally, Table 14 through Table 17 correspond to the self-
test range converted to LSBs and can be compared with the
measured self-test change when operating at a VS of 3.3 V. For
other voltages, the minimum and maximum self-test output
values should be adjusted based on (multiplied by) the scale
factors shown in Table 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 Table 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.
Data Sheet ADXL312
Rev. A | Page 27 of 32
DATA FORMATTING OF UPPER DATA RATES
Formatting of output data at the 3200 Hz and 1600 Hz output
data rates changes depending on the mode of operation (full-
resolution or fixed 10-bit) and the selected output range.
When 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 33. 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
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 34.
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 accel-
eration. Therefore, in these modes of operation, Bit D0 is not
always 0 when output data is right justified, and Bit D6 is not
always 0 when output data is left justified. Operation at any data
rate of 800 Hz or lower also provides a valid LSB in all ranges and
modes that changes according to the applied acceleration.
0D1D2D3
D4D5D6
D7
D0
D1D2
D3
D4
D5
D6
D7
D0D1D2
D3
D4
D5
D6
D7
D0
D1D2D3D4D5D6D7
DATAx1 REGI S TER DATAx0 REGI S TER
OUT P UT DAT A- WO RD FOR
±12g, FULL-RESOLUTION MODE. OUT P UT DAT A- WO RD FOR ± 1. 5g, 10- BIT
AND ±1.5g,FULL-RESOLUTION MODES.
THE ± 3g AND ± 6g FULL-RESOLUTION MODES HAVE THE SAME LSB LOCATION AS THE±1.5g
AND ±12g FULL-RESOLUTION MODES, BUT THE MSB LOCATION CHANGES TO BIT D2 AND
BIT D3 OF THE DAT Ax1 RE GI S TER F OR ±3gAND ±6g, RESPECTIVELY.
08791-145
Figure 33. Data Formatting of Full-Resolution and ±1.5 g, 10-Bit Modes of Operation When Output Data Is Right Justified
0D1D2D3
D4D5
D6
D7
D0D1D2
D3D4
D5D6
D7
D0D1D2D3D4
D5D6
D7
D0D1D2D3
D4
D5D6
D7
DATAx1 REGI S TER DATAx0 REGI S TER
MSB FOR ALL MODES
OF OPERATION WHEN
LEFT JUSTIFIED.
LSB FOR ±1.5g, FULL-RESOLUTION
AND ±1.5g, 10-BIT M ODES .
LSB FOR ±3g, FULL-RESOLUTION MODE.
LSB FOR ±6g, FULL-RESOLUTION MODE.
LSB FO R ±12g, FULL-RESOLUTION MODE.
FO R 3200Hz AND 1600Hz OUT P UT DAT A RATES, T HE LSB I N THESE M ODES IS AL WAYS 0.
ADDIT IO NALL Y, ANY BITS TO THE RI GHT OF THE LSB ARE ALW AY S 0 WHEN THE O UTPUT
DATA IS LEFT JUSTIFIED.
08791-146
Figure 34. Data Formatting of Full-Resolution and ±1.5 g, 10-Bit Modes of Operation When Output Data Is Left Justified
ADXL312 Data Sheet
Rev. A | Page 28 of 32
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 Table 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 35 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.
0.01 0.1
110 100 1k 10k
10
100
1k
10k
AV E RAGING PE RIOD, (s)
ALLAN DEVIATION (µg)
X-AXIS
Y-AXIS
Z-AXIS
08791-251
Figure 35. Root Allan Deviation
70
80
90
100
110
120
130
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
SUPPLY VOLTAGE, V
S
(V)
PERCENTAGE OF NORMALIZED NOISE (%)
X-AXIS
Y-AXIS
Z-AXIS
08791-252
Figure 36. Normalized Noise vs. Supply Voltage, VS
Data Sheet ADXL312
Rev. A | Page 29 of 32
AXES OF ACCELERATION SENSITIVITY
A
Z
A
Y
A
X
08791-042
Figure 37. Axes of Acceleration Sensitivity (Corresponding Output Voltage Increases When Accelerated Along the Sensitive Axis)
GRAVITY
X
OUT
= +1g
Y
OUT
= 0g
Z
OUT
= 0g
XOUT = –1g
YOUT = 0g
ZOUT = 0g
TOP
XOUT = 0g
YOUT = +1g
ZOUT = 0g
TOP
XOUT = 0g
YOUT = –1g
ZOUT = 0g
TOP
XOUT = 0g
YOUT = 0g
ZOUT = +1g
XOUT = 0g
YOUT = 0g
ZOUT = –1g
TOP
08791-043
Figure 38. Output Response vs. Orientation to Gravity
ADXL312 Data Sheet
Rev. A | Page 30 of 32
SOLDER PROFILE
SUPPLIER T
P
≥T
C
MAXIMUM RAMP UP RATE = 3°C/s
MAXIMUM RAMP DOWN RATE = 6°C/s
PREHEAT AREA
T
C
T
C
–5°C
T
C
–5°C
T
SMAX
T
L
T
P
t
P
t
L
t
S
USER T
P
≤T
C
SUPPLIER
t
P
USER
t
P
TEMPERATURE
TIME
TIME 25°C TO PEAK
25
T
SMIN
08791-300
Figure 39: Recommended Soldering Profile
Table 23: Recommended Soldering Profile1, 2
Profile Feature
Condition
Sn63/Pb37 Pb-Free
Average Ramp Rate (TL to TP) 3°C/second maximum
Preheat
Minimum Temperature (TSMIN) 100°C 150°C
Maximum Temperature (TSMAX) 150°C 200°C
Time (TSMIN to TSMAX) (tS) 60 to 120 seconds 60 to 180 seconds
TSMAX to TL
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.
Data Sheet ADXL312
Rev. A | Page 31 of 32
OUTLINE DIMENSIONS
1
0.50
BSC
BOTTOM VIEWTOP VIEW
PIN 1
INDICATOR
32
9
16
17
2425
8
EXPOSED
PAD
PIN 1
INDICATOR
SEATING
PLANE
0.05 M AX
0.02 NO M
0.20 REF
COPLANARITY
0.05
0.30
0.25
0.18
5.10
5.00 SQ
4.90
1.55
1.45
1.35
FOR PRO P E R CONNECT IO N OF
THE EXPOSED PAD, REFER TO
THE PIN CO NFI G URATI ON AND
FUNCTION DES CRIPT IO NS
SECTION OF THIS DATA SHEET.
0.45
0.40
0.35
0.20 M IN
3.70
3.60 SQ
3.50
COM P LIANT T O JEDEC S TANDARDS M O-254-LJJD.
05-29-2012-B
Figure 40. 32-Lead Lead Frame Chip Scale Package [LFCSP_LQ]
5 mm × 5 mm Body, Thick Quad
(CP-32-17)
Dimensions shown in millimeters
08791-038
0.30 mm
0.30 mm
0.30 mm 0. 50 mm
3.60 mm
5.34 mm
0.57 mm
TOP VIEW
Figure 41. Sample Solder Pad Layout (Land Pattern)
ADXL312 Data Sheet
Rev. A | Page 32 of 32
ORDERING GUIDE
Model1, 2 Measurement Range
Specified
Voltage (V)
Temperature
Range Package Description
Package
Option
ADXL312WACPZ ±1.5 g, ±3 g, ±6 g, ±12 g 3.3 −40°C to +105°C 32-Lead LFCSP_LQ CP-32-17
ADXL312WACPZ-RL ±1.5 g, ±3 g, ±6 g, ±12 g 3.3 −40°C to +105°C 32-Lead LFCSP_LQ CP-32-17
ADXL312ACPZ ±1.5 g, ±3 g, ±6 g, ±12 g 3.3 −40°C to +105°C 32-Lead LFCSP_LQ CP-32-17
ADXL312ACPZ-RL ±1.5 g, ±3 g, ±6 g, ±12 g 3.3 −40°C to +105°C 32-Lead LFCSP_LQ CP-32-17
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).
©2010–2015 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08791-0-7/15(A)
