Dual-Axis, 60
to 480
Sensor
with SPI and PSI5
Data Sheet
ADXL251
Rev. SpB Document Feedback
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FEATURES
User selectable sensor g ranges: ±60 g, ±120 g, ±240 g, ±480 g
Dual x-axis and y-axis sensor
Compliant to PSI5 Version 2.1 airbag substandard
Synchronous operation
PSI5-P10P-500/3L and others
Daisy-chain operation with bidirectional communication
Application level serial peripheral interface (SPI)
communication
Selectable 16-bit or 10-bit sensor data
Independently programmable g range and time slot for each
axis
Independent fault discrimination for each axis
Fully differential analog signal chain
0.25 μs data interpolation routine
User selectable, continuous auto-zero operation
High resistance to electromagnetic interference (EMI) and
radio frequency interference (RFI)
SPI mode supply voltage: 3.3 V and 5 V, +5%
PSI5 mode supply voltage range: 4.5 V to 11.0 V
Qualified for automotive applications
APPLICATIONS
Front impact crash sensing
Side impact crash sensing
GENERAL DESCRIPTION
The ADXL251 is a dual-axis, integrated satellite sensor with
user selectable g ranges, compliant to the PSI5 Version 2.1 airbag
substandard, and backwards compliant to PSI5 Version 1.3.
The ADXL251 (x-axis/y-axis) enables low cost solutions for
front impact and side impact airbags, as well as satellite sensor
and electronic control unit (ECU) main sensor applications.
Acceleration data is sent to the control module via a digital,
2-wire current loop PSI5 bus. Communication via the SPI bus
is also available for ECU applications.
The device uses an ECC protected one time programmable
(OTP) memory. The sensor g range is configurable to provide
full-scale measurement of ±60 g, ±120 g, ±240 g, or ±480 g
acceleration. The user can program each axis independently
with multiple g ranges in different time slots. In PSI5 mode,
there are four programmable time slots available. The device
transmits 16-bit or 10-bit acceleration data to the control
module, and can be configured to include either a 1-bit parity
check, or a 3-bit cyclic redundancy check (CRC).
The ADXL251 is available in a 4 mm × 4 mm LFCSP package
and is specified to operate over the full automotive temperature
range, −40°C to +125°C.
FUNCTIONAL BLOCK DIAGRAM
SENSOR ANALOG FRONT END (SAFE)
DEMOD
DIGITAL
FILTER
–3dB AT
400Hz
OFFSET/
SENSITIVITY
CALIBRATION
TIMING
GENERATOR
AUTO-
ZERO
SERIAL
PORT
MASTER
STATE
MACHINE
REGISTER
FILE
ECC
NVM
REPAIR
NVM
CONTROL
POR
TEST MUX
CLOCK
V
DD
MONITOR
SPI
DLL
PSI5
DLL
SPI
PHY
MISO
MOSI
SCLK
CS
PSI5
PHY
V
DD
REG
OFFSET
OVER-
RANGE
SELF
TEST
CHECK
OFFSET
OVR
ERROR
FLAG
OUTPUT
DATA
REGISTER
g RANGE
SENSOR DIGITAL SIGNAL PROCESSING COMMUNICATIONS INTERFACE
SELF
TEST
ERROR
FLAG
SELF
TEST
Σ-∆ MOD
SENSOR
DRIVERS
DUAL-AXIS
ACCELERATION
SENSOR DIE
X-AXIS
STATE
MACHINE
ERROR
HANDLER
OTP NVM
(eFuse)
V
DDIO
I
DATA
V
BP
TP1
DCC/TP2
V
BN
V
DD
AC
AMP
CAP
DETECT
SENSOR ANALOG FRONT END (SAFE)
DEMOD
DIGITAL
FILTER
–3dB AT
400Hz
OFFSET/
SENSITIVITY
CALIBRATION
TIMING
GENERATOR
AUTO-
ZERO
OFFSET
OVER-
RANGE
SELF
TEST
CHECK
OFFSET
OVR
ERROR
FLAG
OUTPUT
DATA
REGISTER
g RANGE
SENSOR DIGITAL SIGNAL PROCESSING
SELF
TEST
ERROR
FLAG
SELF
TEST
Σ-∆ MOD
SENSOR
DRIVERS
Y-AXIS
STATE
MACHINE
AC
AMP
Y-AXIS ONLY
Y-AXIS ONLY
Y-AXIS ONLY
X-AXIS ONLY
X-AXIS ONLY
X-AXIS ONLY
X-AXIS/Y-AXIS
15454-001
Figure 1.
For more information about the ADXL251, contact the Analog Devices, Inc., Customer Interaction Center at
http://www.analog.com/technical_support to connect with a technical support specialist.
