Improved Low Cost
±5
g Dual-Axis
Accelerometer with
Ratiometric Analog Outputs
MXR7305VF
FEATURES
Dual axis accelerometer fabricated on a single CMOS IC
Monolithic design with mixed mode signal processing
RoHS compliant
On-chip sensitivity compensation for temperature
variations
On Demand Self Test
± 5g dynamic range, 250mV/g sensitivity
Independent axis programmability (special order)
Resolution better than 1mg
Zero-g Output Temperature drift, better than ±80mg
over –40~95degC range
27Hz bandwidth
>50,000 g shock survival rating
4.50V to 5.25V single supply operation
Small surface mount package, 5mm x 5mm x 2mm
Improved thermal gradient performance
APPLICATION
Automotive –
Roll over sensing, VSC/EPB application
GENERAL DESCRIPTION
The MXR7305VF 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 250mV/g.
The MXR7305VF provides a g-proportional ratiometric
analog output above/below the zero-g point at 50% of the
supply voltage.
(Ref. other MEMSIC data sheets for absolute analog or
digital outputs).
The typical noise floor is 0.6mg /
Hz
, allowing signals
below 1mg to be resolved at 1Hz bandwidth. The 3dB roll-
off of the device occurs at 27Hz.
The MXR7305V is available in a low profile LCC surface
mount package (5mm x 5mm 2mm). It is hermetically
sealed and operational over a -40°C to +95°C temperature
range.
MXR7305V 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 and particle
problems associated with competitive devices and provide
shock survival greater than 50,000 g, 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 MXR7305V,
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 MXR7305V Rev.A
Page 1 of 6
6/18/2009
MXR7305VF SPECIFICATIONS
(Measurements
@ 25°C, Acceleration = 0 g unless otherwise noted; V
DD
= 5.0V
unless otherwise specified)
Parameter
SENSOR INPUT
Measurement Range
1
No linearity
Conditions
Each Axis
Best fit straight line
±1g
input range, least squares fit
Min
±5.0
0.5
±0.2
±0.5
1.0
20
±2.0
MXR7305V
Typ
Max
Units
g
% of FS
mg
degrees
%
Alignment Error
2
Transverse Sensitivity
3
SENSITIVITY
Each Axis
Sensitivity, Analog Outputs at pins
Xout and Yout
4
@5.0V supply
Sensitivity Ratiometricity
5V+/-5%
6
Change over Temperature
Δ
from 25°C –40°C to +95°C
nd
6
Change over Temperature with 2 Temp Comp
Change over Temperature with aging
Change over Temperature with 2
nd
Temp Comp and
aging
6,8
ZERO g BIAS LEVEL
Each Axis
0 g Offset
0 g Voltage
0 g Offset Ratiometricity
5V+/-5%
0 g Offset over Temperature
Δ
from 25°C, based on 250mV/g
With 2
nd
Temp Comp
0g Offset over Temp with aging
6,
Δ
from 25°C, based on 250mV/g
With 2
nd
Temp Comp
0g
Δ
Offset over Temp
6,7
max-min from -20°C to +80°C
max-min from 0°C to 60°C
NOISE PERFORMANCE
–40°C to +95°C
Noise Density, rms
FREQUENCY RESPONSE
3dB Bandwidth
Phase delay
at 5Hz
SELF TEST
Delta Output changes at Xout, Yout
at 25°C, 0g input
235
-6
-3
-6
-4
250
1.0
265
2.0
+3
+3
+4
+4
mV/g
%
%
%
%
%
-0.20
2.45
-80
-40
-120
-80
0
0
0.00
2.5
+0.20
2.55
1.0
80
40
120
80
60
50
1.5
30
g
V
%
mg
mg
mg
mg
mg
mg
mg/
Hz
Hz
deg
mV
mV
mV
mV
mV
mV
V
V
mS
Kohms
0.6
24
27
-18
-830
-850
-900
at 25°C, 1g input
at 25°C, -1g input
-40
°C~95°C,
0g input
-40
°C~95°C,
1g input
-40
°C~95°C,
-1g input
Selftest Input Voltage
Selftest Response Time
Self Test Pin Pull-Down Resistor (Internal)
Xout and Yout OUTPUTS
Normal Output Range
(Guaranteed symmetric clipping)
Current
Resistance
Capacitance
Turn-On Time
POWER SUPPLY
Operating Voltage Range
Supply Current
5
TEMPERATURE RANGE
Operating Range
PRESSURE RANGE
Operating Range
High
Low
-650
-700
-600
-600
-500
-600
4.0
20
-1000
-1050
-1100
-1100
-1500
-1600
1.0
30
25
50
0.5
Source or sink, @ 4.5V-5.25V
supply
4.5
100
100
100
200
5.25
5.0
+95
300
V
μA
ohm
pF
mS
V
mA
°C
KPa.
@5.0V Supply
4.5
3.2
-40
40
80
5.0
4.1
@ 5.0V RMS
MEMSIC MXR7305VF Rev.A
Page 2 of 6
6/18/2009
X=2.25V
Y=2.50V
NOTES
Guaranteed by measurement of initial offset and sensitivity.
Alignment error is specified as the angle between the true and indicated
axis of sensitivity.
3
Transverse sensitivity is the algebraic sum of the alignment and the
inherent sensitivity errors.
4
The device operates over a 4.5V to 5.25V supply range. The output zero
g reference voltage scales 50% of the supply voltage. Sensitivity has a
linear scale over the supply range of 4.5 to 5.25 volts according to the ratio
(Vdd/5.0 volts) x (250mV/g).
recommended to filter with a minimum of 200Hz low pass filter.
5
Note that the accelerometer has a constant heater power control circuit
thereby requiring higher supply current at lower operating voltage
6
Based on characterization data of 3lotsx30 parts per lot
7
Calculated by MAX-MIN
8
Pending for qualification data
2
1
X=2.50V
Y=2.75V
TOP VIEW
(Not to Scale)
X=2.50V
Y=2.25V
X=2.50V
Y=2.50V
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage (V
DD
, V
DA
) ¹ ……………...-0.5 to +7.0V
Storage Temperature ……….…………-70°C to +150°C
Storage Pressure…………………………………1,378 kPa
Acceleration (any axis, Un-powered for 0.5 msec)..50,000 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.
X=2.75V
Y=2.50V
EARTH’S SURFACE
Note:
The MEMSIC logo’s arrow indicates the -X sensing
direction of the device.
The +Y sensing direction is rotated 90° away from the
+X direction.
Small circle indicates pin one (1).
Pin Description: LCC-8 Package
Pin
1
2
3
4
5
6
7
8
Name
ST
IN
CLK
COM
NC
NC
Y
OUT
X
OUT
V
DD
Description
Self -Test Input
To be grounded.
(Optional Serial Clock Input)
Ground
No Connect
No Connect
Y-Channel Ratiometric Output
X-Channel Ratiometric Output
Supply Voltage 4.5 to 5.25 V
¹
Exposure for up to 60 minutes to absolute maximum ratings for supply
voltages will not affect device reliability.
Package Characteristics
Package
θ
JC
θ
JA
LCC-8
110°C/W
22°C/W
Device Weight
< 1 gram
Ordering Guide
Model
MXR7305VF
Package Style
LCC-8 SMD*
* Parts are shipped in tape and reel packaging.
Caution
ESD (electrostatic discharge) sensitive device.
ESD Compliance:
The MXR7305V sensor is in compliance with the following ESD
standards:
Human Body and 2500V per AEC-Q100-002 Rev. E
Machine Model and 250V per AEC-Q100-003 Rev. E
Mounting Orientation:
The package orientation of the MXR7305V does not affect the
performance of the sensor. The specifications as stated in page 2
remain the same.
Thus, if the sensor is installed with one of its axis of sensitivity in
the vertical plane, it detects accelerations in the Z-axis.
MEMSIC MXR7305VF Rev.A
Page 3 of 6
6/18/2009
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 MXR7305V, one to
measure acceleration in the x-axis and one to measure
acceleration in the Y-axis. For more details visit the
MEMSIC website at www.memsic.com for a
picture/graphic description of the free convection heat
transfer principle.
Y
OUT
– (pin 6)
Y-axis acceleration signal output.
It is capable of sinking or sourcing up to 100μA. The user
should ensure the load impedance is sufficiently high as to
not source/sink >100μA. While the sensitivity of this axis
has been programmed at the factory to be the same as the
sensitivity for the X-axis, the MXR7305V can be
programmed for non-equal sensitivities on the X- and Y-
axes.
Contact Memsic’s local office for additional information.
NC
– (pin 5, 4) No connect. These pins can be tied to
common if the application does not allow pins to remain
unconnected.
COM
– (pin 3) This is the ground pin for the MXR7305V
CLK
– (pin 2) This is an optional serial clock input. The
standard product is delivered with an internal clock (1000
kHz. However, an external clock between 400 kHz and 1.6
MHz can be used as an option, if the sensor is programmed
from the factory to run in external clock mode.
This pin is grounded internally with a 50 Kohm resistor if
an external clock is used it should be able to drive this load.
But if external clock is not used, in order to minimize noise
and ESD this pin should be grounded externally as well.
ST
IN
–
(pin 1) Self –Test Input
This pin controls the self-test function of the sensor
.
Bringing ST
IN
high will cause a negative deflection around
830mV to the Xout and Yout from the 0g value
.
PIN DESCRIPTIONS
V
DD
– (pin 8). Supply voltage input for digital and analog
circuits.
For proper operation
V
DD
must be between 4.50 and 5.25
volts. Refer to the section on PCB layout and fabrication
suggestions for guidance on external parts and connections
recommended.
X
OUT
– (pin 7). X-axis acceleration signal output
It is capable of sinking or sourcing up to 100μA. The user
should ensure the load impedance is sufficiently high as to
not source/sink >100μA. While the sensitivity of this axis
has been programmed at the factory to be the same as the
sensitivity for the Y-axis, the MXR7305V can be
programmed for non-equal sensitivities on the x- and y-
axes.
Contact Memsic’s local office for additional information.
AOU
Xout
T
Y
–
AOUT
Yout
X
Self
Test
0 10 20 30 40 50 60 70 80 90 100110
Time - millisec
MEMSIC MXR7305VF Rev.A
Page 4 of 6
6/18/2009
SELF-TEST DESCRIPTION
When Self-test is enabled the sensitivity compensation is
turned off (disabled). With the sensitivity compensation
disabled, the sensitivity will change according to the
equation below:
S
i
x T
i2.8
= k x S
f
x T
f2.8
sensitive to sensor structure defect and damage. As long as
initial offset is within specification the sensor is functioning
correctly.
The sensor structure for the Thermal technology is
guaranteed to fall outside the specified initial zero g offset
parameters if the sensor is damaged or thermopile is failing.
In most cases this will result in the output voltage hitting
the rail at 5.0 volts.
PCB LAYOUT AND FABRICATION SUGGESTIONS
Reference figure and the notes below for recommendations
on connecting a power source to the MEMSIC device and
PCB fabrication.
ST OFF
X=2.50V
Y=2.50V
ST ON
X=1.70V
Y=1.70V
EARTH’S SURFACE
where S
i
is the sensitivity at any initial temperature T
i
, and
S
f
is the sensitivity at any other final temperature T
f
with
the temperature values in
°C,
k is the ratio between
uncompensated sensitivity and compensated sensitivity at
25°C.
2.5
Sensitivity (normalized)
2.0
1.5
1.0
0.5
0.0
-40
-20
0
20
40
60
80
100
Temperature (C)
PCB Layout
Thermal Accelerometer Sensitivity
.
Accelerometer Position Relative to Gravity
Note1: When the temperature compensation is disabled and
self-test is enabled. Self-test follows different gas law from
sensitivity temperature dependence. It changes much
smaller than sensitivity; this is why the temperature
compensation is not done on self-test conditions.
Note2: Initial offset monitoring is a much better and
reliable method to ensure sensor integrity, since it is ultra
MEMSIC MXR7305VF Rev.A
Page 5 of 6
Notes:
1. C
1
= 1.0μF
2. The capacitor should be located as close as possible to
the device supply pin V
DD
, since the internal heater is
in PWM (1MHz) control mode, with all V
DD
on the
heater at some portion of the time, by using larger
value capacitor can minimize the induced noise on the
outputs.
3. The CLK is grounded internally with a 50 kOhm
resistor, however, in order to minimize noise and ESD
this pin should be grounded externally as well.
4. Robust low inductance ground wiring should be used.
5. Care should be taken (like isolated rings and planes,
signal route out perpendicular to the external thermal
gradient) to ensure there is “thermal symmetry” on the
PCB immediately surrounding the MEMSIC device
and that there is no significant heat source nearby since
it may cause a temperature gradient (“thermal
gradient”) across MEMSIC device, thus result in
performance change (additional initial offset and offset
drift).
6/18/2009
MEMSIC
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