Low Profile, Low Consumption
±0.5
g
Dual Axis Accelerometer with
Absolute Analog Outputs
MXA6500E
FEATURES
Low power consumption: typical 2mA@3V
Resolution better than 1 milli-g
Dual axis accelerometer fabricated on a monolithic
CMOS IC
On chip mixed signal processing
No moving parts
No loose particle issues
>50,000
g
shock survival rating
5mm X 5mm X 1.55mm LCC package
2.7V to 3.6V single supply continuous operation
Ultra low initial Zero-g Offset
No adjustment needed outside
TEMP
TP
Internal
Oscillator
VREF
Temperature
Sensor
TEMP
CLK
PD
CLK
Heater
Control
Coarse
Gain Adj.
Fine Gain
Adj.
No
Connection
Vref
Low Pass Buf.
Filter
CLK
No
Connection
VDD
X aixs
CLK
Coarse
Gain Adj.
Temp
Comp.
A/D
D/A
CLK
Vref
Xout
CLK TEMP CLK
Fine Gain
Adj.
Temp
Comp.
Y aixs
Acceleration
Sensor
CLK
A/D
CLK
D/A
CLK
Low Pass Buf.
Filter
CLK
Yout
CLKTEMP
GND
APPLICATIONS
Tilt and motion sensing in cost-sensitive applications
Smart handheld devices
Computer security
Input devices
Pedometers and activity monitors
Gaming controllers
Toys and entertainment products
GENERAL DESCRIPTION
The MXA6500E is a low cost; dual axis accelerometer
fabricated on a standard, submicron CMOS process. It is a
complete sensing system with on-chip mixed signal
processing. The MXA6500E measures acceleration with a
full-scale range of
±0.5
g
and a sensitivity of 500mV/g @3V
at 25
°C
. It can measure both dynamic acceleration (e.g.
vibration) and static acceleration (e.g. gravity). The
MXA6500E design is based on heat convection and requires
no solid proof mass. This eliminates stiction and particle
problems associated with competitive devices and provides
shock survival greater than 50,000
g,
leading to significantly
lower failure rate and lower loss due to handling during
assembly and at customer field application.
MXA6500E FUNCTIONAL BLOCK DIAGRAM
The max noise floor is 1 mg/
Hz
allowing signals below
1 milli-g to be resolved at 1 Hz bandwidth.
The
MXA6500E is packaged in a hermetically sealed lowprofile
LCC surface mount package (5 mm x 5 mm x 1.55 mm
height)
.
It is operational over a -40°C to +85°C temperature
range.
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.
800 Turnpike St., Suite 202, North Andover, MA 01845
Tel: 978.738.0900
Fax: 978.738.0196
www.memsic.com
MEMSIC MXA6500E Rev.B
Page 1 of 6
3/22/2005
MXA6500E SPECIFICATIONS
(Measurements @ 25°C, Acceleration = 0
g
unless otherwise noted; V
DD
= 3.0V unless otherwise
specified)
MXA6500E
Parameter
SENSOR INPUT
Measurement Range
1
Nonlinearity
Alignment Error
2
Alignment Error
Cross Axis Sensitivity
3
SENSITIVITY
Sensitivity,
Sensitivity Change over
Temperature
4
ZERO
g
BIAS LEVEL
0
g
Offset
0 g Offset
0
g
Offset vs. Temperature
4
NOISE PERFORMANCE
Noise Density, rms
FREQUENCY RESPONSE
3dB Bandwidth
POWER SUPPLY
Operating Voltage Range
Quiescent Supply Current
OUTPUTS PERFORMANCE
Output High Voltage
Output Low Voltage
Current
Turn-On Time
5
TEMPERATURE RANGE
Operating Range
NOTES
1
2
Conditions
Each Axis
Min
±0.5
Typ
Max
Units
g
0.5
±1.0
0.01
±2
1.0
% of FS
degrees
degrees
%
mV/g
%
Best fit straight line
X Sensor to Y Sensor
Each Axis
V
DD
= 3.0V
Delta from 25°C at -40°C
Delta from 25°C at +85°C
Each Axis
VDD = 3.0V
Delta from 25°C
@25°C
15
2.7
@3.0V supply
@3.0V supply
Source or sink @ 3.0V-3.6V Supply
@3.0V supply
-40
2.30
475
500
525
155
-50
1.20
-0.10
1.25
0.00
0.5
0.4
17
1.30
0.10
V
g
mg/°C
mg/
Hz
Hz
V
mA
V
V
uA
mS
+85
°C
1.0
19
3.6
2.0
0.20
100
75
Guaranteed by measurement of initial offset and sensitivity.
Alignment error is specified as the angle between the true and indicated axis of
sensitivity.
3
Cross axis sensitivity is the algebraic sum of the alignment and the inherent
sensitivity errors.
Defined as the output change from ambient to maximum temperature or ambient to
minimum temperature.
5
Output settled to within
±17mg.
4
MEMSIC MXA6500E
Rev.B
Page 2 of 6
3/22/2005
ABSOLUTE MAXIMUM RATINGS*
………………...-0.5 to +7.0V
Supply Voltage (V
DD
)
Storage Temperature ……….…………-65°C to +150°C
Acceleration ……………………………………..50,000
g
*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.
Pin Description: LCC-8 Package
Pin
Name
Description
1
PD
Power Down Control
2
TP
Connect to ground
3
COM
Common
4
NC
Do Not Connect
5
NC
Do Not Connect
6
Yout
Y Channel Output
7
Xout
X Channel Output
8
V
DD
2.7V to 3.6V
Ordering Guide
Model
Package Style
LCC8
MXA6500EP
RoHS compliant
LCC8, Pb-free
MXA6500EB
Temperature Range
-40 to 85°C
-40 to 85°C
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. The proof mass in the MEMSIC
sensor is a gas.
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 accelerometer, one to
measure acceleration in the x-axis and one to measure
acceleration in the y-axis. Please visit the MEMSIC
website at www.memsic.com for a picture/graphic
description of the free convection heat transfer principle.
All parts are shipped in tape and reel packaging.
Caution:
ESD (electrostatic discharge) sensitive device.
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 following the right-hand rule. Small
circle indicates pin one(1)
MEMSIC MXA6500E
Rev.B
Page 3 of 6
3/22/2005
Sensitivity (normalized)
PIN DESCRIPTIONS
V
DD
– This is the supply input for the circuits and the
sensor heater in the
accelerometer
. The DC voltage should
be between 2.7 and 3.6 volts. Refer to the section on PCB
layout and fabrication suggestions for guidance on external
parts and connections recommended.
COM–
This is the ground pin for the
accelerometer
.
TP-
This pin should be connected to the ground.
Xout
– This pin is the output of the x-axis acceleration
sensor. 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
accelerometer
can be programmed for non-equal sensitivities
on the x- and y-axes. Contact the factory for additional
information.
Yout
–
This pin is the output of the y-axis acceleration
2.5
2.0
1.5
1.0
0.5
0.0
-40
-20
0
20
40
60
80
100
Temperature (C)
Thermal Accelerometer Sensitivity
In gaming applications where the game or controller is
typically used in a constant temperature environment,
sensitivity might not need to be compensated in hardware
or software. Any compensation for this effect could be
done instinctively by the game player.
For applications where sensitivity changes of a few percent
are acceptable, the above equation can be approximated
with a linear function. Using a linear approximation, an
external circuit that provides a gain adjustment of –1.1%/°C
would keep the sensitivity within 10% of its room
temperature value over a 0°C to +50°C range.
For applications that demand high performance, a low cost
micro-controller can be used to implement the above
equation. A reference design using a Microchip MCU (p/n
16F873/04-SO) and MEMSIC developed firmware is
available by contacting the factory. With this reference
design, the sensitivity variation over the full temperature
range (-40°C to +85°C) can be kept below 3%. Please visit
the MEMSIC web site at
www.memsic.com
for reference
design information on circuits and programs including look
up tables for easily incorporating sensitivity compensation.
DISCUSSION OF TILT APPLICATIONS AND
RESOLUTION
Tilt Applications:
One of the most popular applications of
the MEMSIC accelerometer product line is in
tilt/inclination measurement. An accelerometer uses the
force of gravity as an input to determine the inclination
angle of an object.
A MEMSIC accelerometer is most sensitive to changes in
position, or tilt, when the accelerometer’s sensitive axis is
perpendicular to the force of gravity, or parallel to the
Earth’s surface. Similarly, when the accelerometer’s axis is
parallel to the force of gravity (perpendicular to the Earth’s
surface), it is least sensitive to changes in tilt.
Following table and figure help illustrate the output
changes in the X- and Y-axes as the unit is tilted from +90°
to 0°. Notice that when one axis has a small change in
output per degree of tilt (in mg), the second axis has a large
change in output per degree of tilt. The complementary
nature of these two signals permits low cost accurate tilt
sensor. 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
accelerometer
can be programmed for non-equal
sensitivities on the x- and y-axes. Contact the factory for
additional information.
PD
–
Pin 1 is the power down control pin. Pull this pin HIGH
will put the accelerometer into power down mode. When the part
goes into power down mode, the total current will be smaller than
0.1uA at 3V.
In normal operation mode, this pin should be connected to
Ground.
COMPENSATION FOR THE CHANGE IN
SENSITIVITY OVER TEMPERATURE
All thermal accelerometers display the same sensitivity
change with temperature. The sensitivity change depends
on variations in heat transfer that are governed by the laws
of physics. The sensitivity change is governed by the
following equation (and shown in following figure in
°C):
S
i
x T
i3.40
= S
f
x T
f3.40
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
°K.
MEMSIC MXA6500E
Rev.B
Page 4 of 6
3/22/2005
sensing to be achieved with the MEMSIC device (reference
application note AN-00MX-007).
Accelerometer Position Relative to Gravity
MEMSIC
POWER SUPPLY NOISE REJECTION
One capacitor is recommended for best rejection of power
supply noise (reference figure below). The capacitor should
be located as close as possible to the device supply pin
(V
DD
). The capacitor lead length should be as short as
possible, and surface mount capacitor is preferred. For
typical applications, the capacitor can be ceramic 0.1 µF.
X-Axis
X-Axis
Orientation
To Earth’s
Surface
(deg.)
90
85
80
70
60
45
30
20
10
5
0
Y-Axis
Change
per deg.
of tilt
(mg)
17.45
17.37
17.16
16.35
15.04
12.23
8.59
5.86
2.88
1.37
0.15
Power Supply Noise Rejection
X Output
(g)
Change
per deg.
of tilt
(mg)
Y Output
(g)
1.000
0.15
0.000
0.996
1.37
0.087
0.985
2.88
0.174
0.940
5.86
0.342
0.866
8.59
0.500
0.707
12.23
0.707
0.500
15.04
0.866
0.342
16.35
0.940
0.174
17.16
0.985
0.087
17.37
0.996
0.000
17.45
1.000
Changes in Tilt for X- and Y-Axes
PCB LAYOUT AND FABRICATION SUGGESTIONS
1.
2.
3.
It is best to solder a 0.1uF capacitor directly across V
DD
and COM pin.
Robust low inductance ground wiring should be used.
Care should be taken to ensure there is “thermal
symmetry” on the PCB immediately surrounding the
MEMSIC device and that there is no significant heat
source nearby.
A metal ground plane should be added directly beneath
the MEMSIC device. The size of the plane should be
similar to the MEMSIC device’s footprint and be as
thick as possible.
Vias can be added symmetrically around the ground
plane. Vias increase thermal isolation of the device
from the rest of the PCB.
Resolution:
The accelerometer resolution is limited by
noise. The output noise will vary with the measurement
bandwidth. With the reduction of the bandwidth, by
applying an external low pass filter, the output noise drops.
Reduction of bandwidth will improve the signal to noise
ratio and the resolution. The output noise scales directly
with the square root of the measurement bandwidth. The
maximum amplitude of the noise, its peak- to- peak value,
approximately defines the worst case resolution of the
measurement. With a simple RC low pass filter, the rms
noise is calculated as follows:
Noise (mg rms) = Noise(mg/
Hz
) *
(
Bandwidth
(
Hz
) *1.6)
The peak-to-peak noise is approximately equal to 6.6 times
the rms value (for an average uncertainty of 0.1%).
4.
5.
MEMSIC MXA6500E
Rev.B
Page 5 of 6
3/22/2005
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