Low Cost
±5
g Dual-Axis Accelerometer
with SPI Interface
Automotive Grade
FEATURES
Dual axis accelerometer fabricated on a single CMOS IC
Monolithic design with mixed mode signal processing
Zero-g temperature stability better than ±30mg from –40C to
105C
Sensitivity temperature compensation better that ±3% from
-40C to 105C
± 5g dynamic range, 800LSB/g sensitivity
29Hz bandwidth
On Demand Self Test
>50,000 g shock survival rating
4.50V to 5.25V single supply operation
Small surface mount package, 5.5mm x 5.5mm x 2.7mm
XZ or XY mounting
RoHS compliant
FM
Control
Register
CLK
Heater
Control
MXP7205VW
VDA
TEMP
Internal
Oscillator
CLK
Coarse
Gain Adj.
Reference
Voltage
Vref
Fine Gain
Adj.
Low Pass
Filter
CLK
SPI
Interface
Low Pass
Filter
CLK
SSB
SCK
MOSI
MISO
Temperature
Sensor
TEMP
X axis
CLK
VDD
Coarse
Gain Adj.
Y axis
Acceleration
Sensor
CLK
Temp
Comp.
A/D
CLK TEMP CLK
Fine Gain
Adj.
Temp
Comp.
A/D
CLKTEMP CLK
GND
•
Vehicle Stability Control
•
Roll Over Detection
•
Electronic Parking Break – Hill Start Assist
•
Headlight Leveling and Steering
GENERAL DESCRIPTION
The MXP7205VW is a low cost, dual axis accelerometer
built on a standard, submicron CMOS process. It measures
acceleration with a full-scale range of
±5g
and a sensitivity
of 800LSB/g with 14bits operation mode and 50LSB/g with
10bits operation mode.
The MXP7205VW provides an SPI interface.
The typical noise floor is 0.6mg /
Hz
, allowing signals
below 1mg to be resolved at 1Hz bandwidth. The inherent
3dB roll off of the device is 29Hz providing immunity to
and attenuation of higher frequency vibrations present in
automotive applications.
The MXP7205VW is packaged in a hermetically sealed
LCC surface mount package (5.5 mm x 5.5 mm x 2.7 mm
height), and the package can be used for either XY and XZ
sensing, its operation temperature is -40°C to +105°C.
AUTOMOTIVE APPLICATIONS
MXP7205VW FUNCTIONAL BLOCK DIAGRAM
MEMSIC’s accelerometer technology allows for designs
from
±1
g to
±70
g with custom versions available above
±70
g. It can measure both dynamic acceleration (e.g.,
vibration) and static acceleration (e.g., gravity).
The design is based on heat convection and requires no
solid proof mass. This eliminates stiction, particle, and
inherent resonant frequency problems associated with
competitive devices and provides shock survivability to
greater that 50,000g, leading to significantly lower failure
rates and lower loss due to handling during assembly and at
customer field application.
Due to the standard CMOS structure of the MXP7205VW,
additional circuitry can easily be incorporated into custom
versions for high volume applications. Contact MEMSIC’s
local office for more information.
Information furnished by MEMSIC is believed to be accurate and reliable.
However, no responsibility is assumed by MEMSIC for its use, nor for any
infringements of patents or other rights of third parties, which may result from
its use. No license is granted by implication or otherwise under any patent or
patent rights of MEMSIC.
©MEMSIC,
Inc.
One Technology Drive, Suite 325, Andover, MA01810, USA
Tel: +1 978 738 0900
Fax: +1 978 738 0196
www.MEMSIC.com
MEMSIC MXP7205VW Rev.C
Page 1 of 11
8/2/2011
MXP7205VW SPECIFICATIONS
(Measurements
@ 25°C, 14bits operation mode, Acceleration = 0 g unless
otherwise noted; V
DD
= V
DA
=5.0V unless otherwise specified)
PARAMETER
Full scale ranges
Nominal Sensitivity
Initial @ 25°C
Sensitivity drift
Sensitivity drift
Cross Axis Sensitivity
Non-Linearity (best straight line)
Zero g Output Offset
Initial @ 25°C
Zero g Output Temperature Drift
Zero g Output Temperature Drift
Total Offset Drift Due to
Temperature
1
Conditions
14bits operation mode
10bits operation mode
Initial -40°C to +105°C
Include Aging
-40°C to +105°C
FSR=10g
2's complement output
Initial -40°C to +105°C
Include Aging
-40°C to +105°C
-40°C to +105°C with
2.5°C/min Temp Ramp
(max-min)
-20°C to +80°C with
2.5°C/min Temp Ramp
(max-min)
0°C to +60°C with
2.5°C/min Temp Ramp
(max-min)
X-axis
Y/Z-axis
25°C
-40°C to +105°C
-40°C to +105°C, include
aging
-60
-30
-60
-3
-3
-4
MIN
-5
TYP
800
50
0
0
MAX
5
UNITS
g
LSB/g
LSB/g
%
%
%
%
%FSR
LSB
mg
mg
mg/°C
mg
mg
+3
+3
+4
2.0
1.0
0
0
0
+60
+30
1.0
+60
80
40
mg
50
mg
Selftest Signal
Selftest Signal Tolerance
Selftest Signal Drift (0g input)
+2.5
-2.5
-5
-5
-8
+5
+5
+8
20
32
12
2
10
1.5
5.5
11
300
5.25
4.5
105
g
g
%
%
%
mS
Hz
mS
mS
mS
mg/sqrtHz
mg RMS
mg RMS
mS
V
mA
°C
Selftest Signal Rise/Fall Time
Frequency Response
Phase Delay
Recover Time From Overload Input
Input Referred Noise Density
RMS
Output Noise
Power up time
2
Operation Power Supply Range
Power consumption
Operation Temperature Range
26
0 to 1KHz
10g, 1mS shock
10000g, 0.5mS half sine
shock
-40°C to +105°C, within
29Hz
No external filtering, 25°C
No external filtering
-40°C to +105°C
4.5
@5V
-40
29
10
0.5
3.5
200
5.0
3.5
Note:
1
: Requirements can be met by characterization of 3lots x 30 parts per lot, not 100% test in production.
2
: Output settled to within +/-17mg of the final value.
MEMSIC MXP7205VW Rev.C
Page 2 of 12
8/2/2011
DIGITAL INTERFACE
SYMBOL
VIH
VIL
Vhys
VOH
VOL
Rin1
Rin2
IPU
CL
SYMBOL
PARAMETER
High Level Input Voltage
Low Level Input Voltage
Hysteresis (SCK, SSB, DI/MOSI)
High Level Output (MISO)
Low Level Output (MISO)
Pull-down resistance
(SCK, DI/MOSI)
Pull-down resistance (FM)
Pull-up Current (SSB)
(SPI mode)
Load Capacitance (MISO)
PARAMETER
SPI Operating Frequency
Data Register Update Rate
SPI Communication Startup Time
SCK High Time
SCK Low Time
SCK Period
SCK Rise/Fall Time
Data Input (MOSI) Setup Time
Data Input (MOSI) Hold Time
Data Out (MISO) Access Time
Data Out(MISO) Valid After SCK
Data Output (MISO) Lag Time
Data Output (MISO) Disable Time
Enable (SSB) Lead Time
Enable (SSB) Lag Time
Sequential Transfer Delay
CONDITIONS
MIN
0.7 x VDD
0.1
VDD-0.4
100
30
10
MAX
0.3 x VDD
0.4
0.4
200
50
50
80
CONDITIONS
MIN
TYP
800
1
.5 x td3 - 13
.5 x td3 - 13
123.7
0.1xVDD -
0.9xVDD
37
49
43
30
0
750
.5 x td3
.5 x td3
1.5 x td3
13
MAX
8.08
UNITS
V
V
V
V
V
kΩ
kΩ
μA
pF
UNITS
MHz
KHz
ms
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Iout = 0.2mA
Iout =
─0.5mA
VDD=4.5-5.5V
td1
td2
td3
tr, tf
td4
td5
td6
td7
td8
td9
td10
td11
td12
SPI Timing
MEMSIC MXP7205VW Rev.C
Page 3 of 12
8/2/2011
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage (V
DD
, V
DA
) ¹ ……………...-0.5 to +7.0V
Storage Temperature ……….…………-55°C to +150°C
Storage Pressure…………………………………1,378 kPa
Acceleration (any axis, Un-powered for 0.5 msec)..50,000 g
Acceleration (any axis, Powered for 0.5 msec)… 10,000 g
Output Short Circuit Duration, any pin to common…….Indefinite
*Stresses above those listed under Absolute Maximum Ratings may cause permanent
damage to the device. This is a stress rating only; the functional operation of the
device at these or any other conditions above those indicated in the operational
sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
Note:
The MEMSIC logo’s arrow indicates the +Z sensing
direction of the device.
Small circle indicates pin one (7).
ESD Compliance:
The MXP7205VW sensor is in compliance with the following
ESD standards:
HBM class H2 per AEC-Q100-002 Rev. E
MM class M2 per AEC-Q100-003 Rev. E
XY Sensing:
7
6
¹
Exposure for up to 60 minutes to absolute maximum ratings for supply
voltages will not affect device reliability.
Ordering Guide
Model
MXP7205VW
Package Style
LCC-8 SMD*
+Z
8
5
* Parts are shipped in tape and reel packaging.
Pin Description: LCC Package
Pin
1
2
3
4
5/J
6/M
7/L
8/K
Name
MISO
V
DA
V
DD
FM
SCK
SSB
VSS
MOSI
Description
Master In - Slave Out
Analog Supply
Digital Supply, V
DA
and V
DD
must be the same voltage
Factory mode (for factory test
only). Connect to VSS
Clock Input
Slave Select Bar (active low)
Ground
Master Out - Slave In
1
2
+X
3
4
(Top View, do not scale)
Note:
Small circle indicates pin seven (7).
XZ Sensing
:
M
L
K
J
Caution
ESD (electrostatic discharge) sensitive device.
X=0
Z=800
1
2
+X
3
4
(Bottom View, do not scale)
X=800
Z=0
TOP VIEW
(Not to Scale)
X=-800
Z=0
X=0
Z=0
EARTH’S SURFACE
X=0
Z=-800
MEMSIC MXP7205VW Rev.C
Page 4 of 12
8/2/2011
THEORY OF OPERATION
The MEMSIC device is a complete dual-axis acceleration
measurement system fabricated on a monolithic CMOS IC
process. The device operation is based on heat transfer by
natural convection and operates like other accelerometers
having a proof mass except it is a gas in the MEMSIC
sensor.
A single heat source, centered in the silicon chip is
suspended across a cavity. Equally spaced
aluminum/polysilicon thermopiles (groups of
thermocouples) are located equidistantly on all four sides of
the heat source (dual axis). Under zero acceleration, a
temperature gradient is symmetrical about the heat source,
so that the temperature is the same at all four thermopiles,
causing them to output the same voltage.
Acceleration in any direction will disturb the temperature
profile, due to free convection heat transfer, causing it to be
asymmetrical. The temperature, and hence voltage output
of the four thermopiles will then be different. The
differential voltage at the thermopile outputs is directly
proportional to the acceleration. There are two identical
acceleration signal paths on the MXP7205VF, one to
measure acceleration in the x-axis and one to measure
acceleration in the y/z-axis. For more details visit the
MEMSIC website at www.MEMSIC.com for a
picture/graphic description of the free convection heat
transfer principle.
MOSI
– This pin serves as the Master Out Slave In (MOSI)
SPI function. The MOSI signal is the serial input data to
the MXP7205VW from the external SPI controller, such as
SPI control register load commands or requests for output
data. .
SCK
– This pin is the SPI clock signal and is used to
transfer data between the MXP7205VW and an external
controller via the MOSI and MISO pins.
SIGNAL PATH FREQUENCY RESPONSE
The frequency response of the MXP7205VW is primarily
determined by the thermal sensor characteristics and a
digital lowpass filter included in the signal path to eliminate
quantization noise and limit thermal noise bandwidth. The
sensor is modelled as a two pole lowpass filter, with real
poles located nominally at 40 Hz and 85 Hz. The lowpass
filter is a second order Butterworth filter with a 3 dB cutoff
frequency of nominally 44 Hz. Sensor poles have a
tolerance of approximately ±10%, and the Butterworth filter
cutoff frequency has a tolerance of approximately ±5%.
The nominal complex transfer function of the signal path is
given by:
H
(
f
)
=
1
•
⎛
f
⎞
1
+
j
⎜ ⎟
1
+
⎝
40
⎠
1
1
•
2
⎛
f
⎞
⎛
f
⎞
j
⎜ ⎟
1
− ⎜ ⎟ +
j
2
⎛
f
⎞
⎜ ⎟
⎝
85
⎠
44
⎠
⎝
⎝
44
⎠
PIN DESCRIPTIONS
V
DD
– This is the digital power supply for the
MXP7205VW. This pin supplies current to the heater
element and digital circuitry. The DC voltage should be
between 4.5V and 5.25V.
V
DA
– This is the analog power supply. This pin supplies
current to the analog circuitry. The DC voltage should be
equal to the voltage supplied to the V
DD
pin.
VSS
– This is the ground pin for the MXP7205VW.
FM
– Factory Mode for factory use only, connect to VSS.
MISO
– This pin serves as the Master In Slave Out (MISO)
SPI function. The MISO signal is the serial output data sent
from the MXP7205VW to the external SPI controller, such
as acceleration output data and status information.
SSB
– This pin serves as the Slave Select Bar (SSB) SPI
function. When SSB is high, communication with the SPI
is disabled; when SSB is low, communication is enabled,
and data can be exchanged between the MXP7205VW and
the external SPI controller.
MEMSIC MXP7205VW Rev.C
Plots of the amplitude (in dB, relative to DC sensitivity)
and phase response (in degrees) of the signal path for
typical, minimum, and maximum sensor and filter pole
frequencies are shown below.
Signal Path Amplitude Response
Page 5 of 12
8/2/2011
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