MXA2500U [ETC]
Ultra Low Noise, 1g Dual Axis Accelerometer with Analog Outputs; 超低噪声，1G双轴加速度计，提供模拟输出
| 型号： | MXA2500U |
| 厂家： | 
ETC |
| 描述： | Ultra Low Noise, 1g Dual Axis Accelerometer with Analog Outputs |
| 文件： | 总8页 (文件大小：322K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Ultra Low Noise, ±1 g Dual Axis
Accelerometer with Analog Outputs
MXA2500U
FEATURES
Better than 1 milli-g resolution
Dual axis accelerometer fabricated on a monolithic
CMOS IC
On-chip mixed mode signal processing
No moving parts
Sck
Internal
Temperature
Sensor
TOUT
Oscillator
(optional)
Voltage
VREF
Reference
CLK
Continous
Self Test
Heater
Control
50,000 g shock survival rating
25 Hz bandwidth expandable to >160 Hz
2.70V to 5.25V single supply continuous operation
Small (5mm x 5mm x 2mm) surface mount package
Continuous self test
Low Pass
X axis
AOUTX
Filter
Factory Adjust
Offset & Gain
Custom programmable specifications
Independent axis programmability (special order)
Low Pass
Filter
Y axis
AOUTY
2-AXIS
SENSOR
APPLICATIONS
Automotive – Vehicle Security/Active Suspension/ABS
Headlight Angle Control/Tilt Sensing
VDD
Gnd
VDA
Security – Gas Line/Elevator/Fatigue Sensing
Office Equipment – Computer Peripherals/PDA’s/Mouse
Smart Pens/Cell Phones
MXA2500U FUNCTIONAL BLOCK DIAGRAM
Gaming – Joystick/RF Interface/Menu Selection/Tilt Sensing
White Goods – Spin/Vibration Control
GENERAL DESCRIPTION
The MXA2500U provides an absolute analog output The
typical noise floor is 0.2 mg/ Hz allowing signals below
1 milli-g to be resolved at 1 Hz bandwidth. The 3dB
rolloff of the device occurs at 25 Hz but is expandable to
>160 Hz (ref. Application Note AN-00MX-003). The
MXA2500U is available in a low profile LCC surface
mount package (5 mm x 5 mm x 2 mm). It is hermetically
sealed and is operational over a -40°C to +105°C
The MXA2500U is an ultra low noise and low cost, dual
axis accelerometer fabricated on a standard, submicron
CMOS process. It is a complete sensing system with on-
chip mixed mode signal processing. The MXA2500U
measures acceleration with a full-scale range of ±1 g and a
sensitivity of 500mV/g at 25°C. (The MEMSIC
accelerometer product line extends from ±1 g to ±10 g with
custom versions available above ±10 g.) It can measure
both dynamic acceleration (e.g., vibration) and static
acceleration (e.g., gravity). The MXA2500U 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 of
50,000 g, leading to significantly lower failure rates and
lower loss due to handling during assembly.
temperature range. It also contains an on-chip temperature
sensor and a bandgap voltage reference.
Due to the standard CMOS structure of the MXA2500U,
additional circuitry can easily be incorporated into custom
versions for high volume applications. Contact the factory
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.
800 Turnpike Street, Suite 202 , North Andover, MA 01845
Tel: 978.738.0900
www.memsic.com
Fax: 978.738.0196
MEMSIC MXA2500U Rev A
Page 1 of 8
5/02
MXA2500U SPECIFICATIONS (Measurements @ 25°C, Acceleration = 0 g unless otherwise noted; VDD, VDA = 5.0V
unless otherwise specified)
MXA2500U
Parameter
Conditions
Min
Typ
Max
Units
SENSOR INPUT
Measurement Range1
Nonlinearity
Each Axis
g
±1.0
Best fit straight line
Each Axis
0.5
±1.0
±2.0
1.0
% of FS
degree
%
Alignment Error2
Transverse Sensitivity3
SENSITIVITY
Sensitivity, Analog Outputs at pins
6
A
OUTX and AOUTY
475
-50
500
525
mV/g
%
%
%
Change over Temperature (uncompensated)4
+100
∆ from 25°C, at –40°C
∆ from 25°C, at +105°C
∆ from 25°C, –40°C to +105°C
Each Axis
Change over Temperature (compensated) 4
<3.0
ZERO g BIAS LEVEL
0 g Offset6
-0.1
0.00
1.25
±0.75
±0.375
+0.1
1.30
g
0 g Voltage6
1.20
V
0 g Offset over Temperature
∆ from 25°C
∆ from 25°C, based on 500mV/g
mg/°C
mV/°C
NOISE PERFORMANCE
Noise Density, rms
Without frequency compensation
0.2
0.4
mg/ Hz
FREQUENCY RESPONSE
3dB Bandwidth - uncompensated
3dB Bandwidth - compensated5
TEMPERATURE OUTPUT
Tout Voltage
25
Hz
Hz
>160
1.23
4.6
1.25
5.0
1.27
5.4
V
mV/°C
Sensitivity
VOLTAGE REFERENCE
VRef
@2.7V-5.25V supply
Source
2.4
2.5
0.1
2.65
100
V
mV/°C
µA
Change over Temperature
Current Drive Capability
SELF TEST
Continuous Voltage at AOUTX, AOUTY under
Failure
@5.0V Supply, output rails to
supply voltage
5.0
2.7
V
V
Continuous Voltage at AOUTX, AOUTY under
Failure
@2.7V Supply, output rails to
supply voltage
AOUTX and AOUTY OUTPUTS
Normal Output Range
@5.0V Supply
@2.7V Supply
0.1
0.1
4.9
2.6
V
V
Current
Turn-On Time
Source or sink, @ 2.7V-5.0V supply
@5.0V Supply
100
100
40
µA
mS
mS
@2.7V Supply
POWER SUPPLY
Operating Voltage Range
Supply Current
2.7
3.0
4.0
5.25
4.2
V
@ 5.0V
@ 2.7V
3.6
4.9
mA
mA
Supply Current6,7
5.8
TEMPERATURE RANGE
Operating Range
-40
+105
°C
NOTES
6
1
The device operates over a 2.7V to 5.25V supply range. Please note that
sensitivity and zero g bias level will be slightly different at 2.7V operation.
For devices to be operated at 2.7V/3.0V in production, they can be
trimmed at the factory specifically for this lower supply voltage operation,
in which case the sensitivity and zero g bias level specifications on this
page will be met. Please contact the factory for specially trimmed devices
for low supply voltage operation.
Guaranteed by measurement of initial offset and sensitivity.
2
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 sensitivity change over temperature for thermal accelerometers is
based on variations in heat transfer that are governed by the laws of
physics and it is highly consistent from device to device. Please refer to
the section in this data sheet titled “Compensation for the Change of
Sensitivity over Temperature” for more information.
7
Note that the accelerometer has a constant heater power control circuit
thereby requiring higher supply current at lower operating voltage.
5
External circuitry is required to extend the 3dB bandwidth. (ref.
Application Note: AN-00MX-003).
MEMSIC MXA2500U Rev A
Page 2 of 8
05/02
8
4
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage (VDD, VDA) ………………...-0.5 to +7.0V
Storage Temperature ……….…………-65°C to +150°C
Acceleration ……………………………………..50,000 g
1
2
3
7
6
5
X +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.
Y +g
Top View
Package Characteristics
Package
Device Weight
< 1 gram
θJA
θJC
22°C/W
LCC-8
110°C/W
Pin Description: LCC-8 Package
Pin
1
Name
TOUT
AOUTY
Gnd
Description
Temperature (Analog Voltage)
Y-Axis Acceleration Signal
Ground
2
3
4
VDA
Analog Supply Voltage
X-Axis Acceleration Signal
2.5V Reference
Optional External Clock
Digital Supply Voltage
5
AOUTX
Vref
Sck
VDD
6
7
8
Ordering Guide
Model
Package Style
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.
A2500UL
LCC-8 SMD*
*LCC parts are shipped in tape and reel packaging.
Caution
ESD (electrostatic discharge) sensitive device.
MEMSIC MXA2500U Rev A
Page 3 of 8
05/02
sensitivities on the x- and y-axes. Contact the factory for
additional information on this feature.
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 stationary element, or ‘proof
mass’, in the MEMSIC sensor is a gas.
TOUT – This pin is the buffered output of the temperature
sensor. The analog voltage at TOUT is an indication of the
die temperature. This voltage is useful as a differential
measurement of temperature from ambient and not as an
absolute measurement of temperature. After correlating the
voltage at TOUT to 25°C ambient, the change in this voltage
due to changes in the ambient temperature can be used to
compensate for the change over temperature of the
accelerometer offset and sensitivity. Please refer to the
section on Compensation for the Change in Sensitivity
Over Temperature for more information.
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.
Sck – The standard product is delivered with an internal
clock option (800kHz). This pin should be grounded
when operating with the internal clock. An external
clock option can be special ordered from the factory
allowing the user to input a clock signal between 400kHz
and 1.6MHz.
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.
V
ref – A reference voltage is available from this pin. It is
set at 2.50V typical and has 100µA of drive capability.
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. Manufacturing variations do not influence the
sensitivity change, so there are no unit-to-unit differences
in sensitivity change. The sensitivity change is governed
by the following equation (and shown in Figure 1 in °C):
PIN DESCRIPTIONS
V
DD – This is the supply input for the digital circuits and
the sensor heater in the accelerometer. The DC voltage
should be between 2.70 and 5.25 volts. Refer to the section
on PCB layout and fabrication suggestions for guidance on
external parts and connections recommended.
Si x Ti2.81 = Sf x Tf2.81
V
DA – This is the power supply input for the analog
amplifiers in the accelerometer. Refer to the section on
PCB layout and fabrication suggestions for guidance on
external parts and connections recommended.
where Si is the sensitivity at any initial temperature Ti, and
Sf is the sensitivity at any other final temperature Tf with
the temperature values in °K.
Gnd – This is the ground pin for the accelerometer.
2.0
1.5
1.0
0.5
0.0
A
OUTX – 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 on this feature.
-40
-20
0
20
40
60
80
100
Temperature (C)
A
OUTY – This pin is the output of the y-axis acceleration
Figure 1: Thermal Accelerometer Sensitivity
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
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
MEMSIC MXA2500U Rev A
Page 4 of 8
05/02
or software. Any compensation for this effect could be
done instinctively by the game player.
X-Axis
Change
Y-Axis
Change
X-Axis
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 –0.9%/°C
would keep the sensitivity within 10% of its room
temperature value over a 0°C to +50°C range.
Orientatio
n
X Output per deg. Y Output per deg.
To Earth’s
(g)
of tilt
(g)
of tilt
Surface
(deg.)
90
(mg)
(mg)
1.000
0.996
0.985
0.940
0.866
0.707
0.500
0.342
0.174
0.087
0.000
0.15
1.37
0.000
0.087
0.174
0.342
0.500
0.707
0.866
0.940
0.985
0.996
1.000
17.45
17.37
17.16
16.35
15.04
12.23
8.59
85
80
2.88
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 +105°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.
70
5.86
60
8.59
45
12.23
15.04
16.35
17.16
17.37
17.45
30
20
5.86
10
2.88
5
1.37
0
0.15
Table 1: Changes in Tilt for X- and Y-Axes
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:
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.
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%).
Table 1 and Figure 2 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 sensing to
be achieved with the MEMSIC device (reference
application note AN-00MX-007).
EXTERNAL FILTERS
AC Coupling: For applications where only dynamic
accelerations (vibration) are to be measured, it is
recommended to ac couple the accelerometer output as
shown in Figure 3. The advantage of ac coupling is that
variations from part to part of zero g offset and zero g
offset versus temperature can be eliminated. Figure 3 is a
HPF (high pass filter) with a –3dB breakpoint given by the
1
equation: f =
. In many applications it may be
X
2πRC
+900
desirable to have the HPF –3dB point at a very low
frequency in order to detect very low frequency
accelerations. Sometimes the implementation of this HPF
may result in unreasonably large capacitors, and the
designer must turn to digital implementations of HPFs
where very low frequency –3dB breakpoints can be
achieved.
gravity
00
Y
Top View
Figure 2: Accelerometer Position Relative to Gravity
MEMSIC MXA2500U Rev A
Page 5 of 8
05/02
COMPENSATION FOR EXTENDING THE
FREQUENCY RESPONSE
C
C
AOUTX
Filtered
Output
AOUTX
The response of the thermal accelerometer is a function of
the internal gas physical properties, the natural convection
mechanism and the sensor electronics. Since the gas
properties of MEMSIC's mass produced accelerometer are
uniform, a simple circuit can be used to equally compensate
all sensors. For most applications, the compensating circuit
does not require adjustment for individual units.
R
R
AOUTY
AOUTY
Filtered
Output
A simple compensating network comprising two
operational amplifiers and a few resistors and capacitors
provides increasing gain with increasing frequency (see
Figure 5). The circuit shown is for an absolute output
accelerometer operating at 5 V supply. It provides a DC
gain of X2, so the offset at the output is 2.5V and the
sensitivity is doubled. The 14.3 KΩ and the 5.9KΩ
resistors along with the non-polarized 0.82µF capacitors
tune the gain of the network to compensate for the output
attenuation at the higher frequencies. The resistors and the
capacitors provide noise reduction and stability.
Figure 3: High Pass Filter
Low Pass Filter: An external low pass filter is useful in
low frequency applications such as tilt or inclination. The
low pass filter limits the noise floor and improves the
resolution of the accelerometer. The low pass filter shown
in Figure 4 has a –3dB breakpoint given by the equation:
1
f =
. For the 200 Hz ratiometric output device
2πRC
14.3K
5.9K
filter, C=0.1µF and R=8kΩ, ±5%, 1/8W.
1.5uF
0.01uF
R
AOUTX
Filtered
Output
AOUTX
UA
-
Aout X or Y
C
8.06K
160K
+
R
AOUTY
Filtered
Output
0.047uF
0.0022uF
AOUTY
C
14.3K
1.5uF
5.9K
0.01uF
Figure 4: Low Pass Filter
USING THE ACCELEROMETER IN VERY LOW
POWER APPLICATIONS (BATTERY OPERATION)
In applications with power limitations, power cycling can
be used to extend the battery operating life. One important
consideration when power cycling is that the accelerometer
turn on time limits the frequency bandwidth of the
accelerations to be measured. For example, operating at
2.7V the turn on time is 40mS. To double the operating
time, a particular application may cycle power ON for
40mS, then OFF for 40mS, resulting in a measurement
period of 80mS, or a frequency of 12.5Hz. With a
frequency of measurements of 12.5Hz, accelerations
changes as high as 6.25Hz can be detected.
UB
-
Freq. Comp. Output
8.06K
+
0.047uF
Figure 5: Frequency Response Extension Circuit
The accelerometer response (bottom trace), the network
response (top trace) and the compensated response (middle
trace) are shown in Figure 6. The amplitude remains above
–3db beyond 100 Hz, and there is useable signal well
after this frequency.
Power cycling can be used effectively in many inclinometry
applications, where inclination changes can be slow and
infrequent.
MEMSIC MXA2500U Rev A
Page 6 of 8
05/02
Various digital compensation techniques can be applied
using a similar concept. Digital techniques can provide
better compensation because they can compensate for non-
linear zero g offset vs. temperature. A micro-controller or
micro-processor would perform the compensation. The
acceleration signal and the temperature signal would be
digitized using an analog to digital converter. Like in the
analog compensation, the first step is to test and
characterize the zero g change. The purpose of the
characterization is to create a look up table or to estimate a
mathematical representation of the change. For example,
the change could be characterized by an equation of the
form:
60
45
30
15
0
-15
-30
-45
-60
10
100
1000
Frequency - Hz
Change = a * Temperature 2 + b * Temperature + c
Figure 6: Amplitude Frequency Response
where a,b,care unique constants for each accelerometer.
In normal operation the processor calculates the output:
Compensated Output = Acceleration – Change.
COMPENSATION FOR ZERO G OFFSET CHANGE
OVER TEMPERATURE
For a more detail discussion of temperature compensation
reference MEMSIC application note #AN-00MX-002.
In applications where a stable zero g offset is required, and
where the AC coupling external filter described earlier can
not be used, analog or digital temperature compensation
can be applied. The compensation requires individual
calibration because the magnitude of the zero g offset
change over temperature is different for each unit. To
compensate the change, a calibrated temperature dependent
signal equal in magnitude but with opposite polarity is
added to the accelerometer output. The circuit in Figure 7
shows a circuit example applying an analog linear
compensation technique. In this circuit the accelerometer
temperature sensor output is added to or subtracted from
the accelerometer output. The calibration sequence is: start
at room temperature with the 100K pot set so that its wiper
is at Vref. Next, soak the accelerometer at the expected
extreme temperature and observe the direction of the
change. Then set the switch to the non-inverting input if the
change is negative or vice versa. Finally, adjust the 100K
pot while monitoring the circuit output, until the zero g
offset change is removed.
TEMPERATURE OUTPUT NOISE REDUCTION
It is recommended that a simple RC low pass filter is used
when measuring the temperature output. Temperature
output is typically a very slow changing signal, so a very
low frequency filter eliminates erroneous readings that may
result from the presence of higher frequency noise. A
simple filter is shown in Figure 8.
8.2K
TOUT
Filtered TOUT
MEMSIC
Accel.
0.1uF
Figure 8: Temperature Output Noise Reduction
Vref
+5V
10K
100K
100K
10K
Aoutx or y
zero drift
compensated
g
SW SPDT
+
-
100K
100K
Tout
10K
Aoutx or y
100K
100K
Figure 7: Zero g Offset Temperature Compensation Circuit
MEMSIC MXA2500U Rev A
Page 7 of 8
05/02
POWER SUPPLY NOISE REJECTION
PCB LAYOUT AND FABRICATION SUGGESTIONS
1. The Sck pin should be grounded to minimize noise.
2. Liberal use of ceramic bypass capacitors is
recommended.
Two capacitors and a resistor are recommended for best
rejection of power supply noise (reference Figure 9 below).
The capacitors should be located as close as possible to the
device supply pins (VDA, VDD). The capacitor lead length
should be as short as possible, and surface mount capacitors
are preferred. For typical applications, capacitors C1 and
C2 can be ceramic 0.1 µF, and the resistor R can be 10 Ω.
In 5V applications where power consumption is not a
concern, maximum supply noise rejection can be obtained
by significantly increasing the values of C1, C2 and R. For
example, C1 = C2 = 0.47 µF and R = 270 Ω will virtually
eliminate power supply noise effects.
3. Robust low inductance ground wiring should be used.
4. 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.
5. A metal ground plane should be added directly beneath
the MEMSIC device. The size of the ground plane
should be similar to the MEMSIC device’s footprint
and be as thick as possible.
6. Vias can be added symmetrically around the ground
plane. Vias increase thermal isolation of the device
from the rest of the PCB.
V SUPPLY
C1
R
C2
VDA
MEMSIC
VDD
Accelerometer
Figure 9: Power Supply Noise Rejection
PACKAGE DRAWING
Fig 10: Hermetically Sealed Package Outline
MEMSIC MXA2500U Rev A
Page 8 of 8
05/02
相关型号：
MXA6500EP
Low Profile, Low Consumption 0.5 g Dual Axis Accelerometer with Absolute Analog Outputs
ETC
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