MXD6125QB [ETC]
Ultra High Performance ±1g Dual Axis Accelerometer with Digital Outputs;
| 型号： | MXD6125QB |
| 厂家： | 
ETC |
| 描述： | Ultra High Performance ±1g Dual Axis Accelerometer with Digital Outputs |
| 文件： | 总6页 (文件大小：100K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Ultra High Performance
±1g Dual Axis Accelerometer with
Digital Outputs
MXD6125Q
FEATURES
Ultra Low Noise 0.13 mg/ Hz typical
Ultra Low Offset Drift 0.1 mg/°C typical
Resolution better than 1 mg
Monolithic CMOS IC
On chip mixed signal processing
50,000 g shock survival rating
Low profile LCC package
2.7V to 3.6V single supply
No adjustment needed outside
APPLICATIONS
Automotive – Vehicle Security/Active Suspension/ABS
Headlight Angle Control/Tilt Sensing
Security – Gas Line/Elevator/Fatigue Sensing
Office Equipment – Computer Peripherals/PDA’s/Mouse
Smart Pens/Cell Phones
MXD6125Q FUNCTIONAL BLOCK DIAGRAM
Gaming – Joystick/RF Interface/Menu Selection/Tilt Sensing
GENERAL DESCRIPTION
The MXD6125Q is a low noise, low profile, dual axis
accelerometer fabricated on a standard CMOS process. It is
a complete sensing system with on-chip mixed mode signal
processing. The MXD6125Q measures acceleration with a
full-scale range of ±1 g and a sensitivity of 12.5%/g @3V at
25°C. It can measure both dynamic acceleration (e.g.,
vibration) and static acceleration (e.g., gravity). The
MXD6125Q design is based on heat convection and requires
no solid proof mass. This eliminates stiction and particle
issues normally found with capacitive based technology, and
significantly lowers field failure rate and in-line loss due to
handling during assembly.
The MXD6125Q provides two ratiometric analog outputs.
The maximum noise floor is 0.18 mg/ Hz allowing signals
below 0.5 mg to be resolved at 1 Hz bandwidth and the 3dB
rolloff of the device occurs at 8 Hz. The MXD6125Q is
available in a hermetically sealed low profile LCC surface
mount package measuring 5mm x 5mm x 1.55m.
.
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
www.memsic.com
Fax: 978.738.0196
MEMSIC MXD6125Q
Page 1 of 6
2/24/2005
MXD6125Q SPECIFICATIONS (Measurements @ 25°C, Acceleration = 0 g unless otherwise noted; VDD = 3.0V unless otherwise
specified)
MXD6125Q
Parameter
Conditions
Units
Min
Typ
Max
SENSOR INPUT
Each Axis
Measurement Range1
g
±1.0
Nonlinearity
Best fit straight line
0.5
±1.0
±2.0
1.0
% of FS
degrees
%
Alignment Error2
Transverse Sensitivity3
SENSITIVITY
Each Axis
D
OUTX and DOUTY
@3.0V supply
11.8
-70
12.5
13.2
170
% duty
cycle/g
%
Change over Temperature
∆ from 25°C@-40°C
∆ from 25°C@105°C
Each Axis
%
ZERO g BIAS LEVEL
0 g Offset
0 g Duty Cycle
-0.04
49.5
0.0
50
+0.04
50.5
g
% duty
cycle
mg/°C
Hz
0 g Offset over Temperature
PWM Frequency
NOISE PERFORMANCE
Noise Density, rms
FREQUENCY RESPONSE
3dB Bandwidth
SELF TEST
Continuous Voltage at DOUTX
OUTY under Failure
Based on 12.5%/g
0.1
100
0.5
105
95
6
0.13
8
0.18
10
mg/ Hz
Hz
V
,
@3.0V Supply, output rails to
supply voltage
3.0
D
DOUTX and DOUTY OUTPUTS
Normal Output Range
Output High
Output Low
2.8
V
V
0.2
Current
Source or sink, @ 2.7V-3.6V
supply
100
µA
Rise/Fall Time
2.7 to 3.6V supply
@3.0V Supply
90
2.7
-40
100
150
110
3.6
nS
mS
Turn-On Time4
POWER SUPPLY
Operating Voltage Range
Supply Current
TEMPERATURE RANGE
Operating Range
3.0
1.5
V
mA
@ 3.0 V
+105
°C
NOTES
1
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 Cross axis sensitivity is the algebraic sum of the alignment and the inherent
sensitivity errors.
4.Settled to within ±17mg.
MEMSIC MXD6125Q
Page 2 of 6
2/24/2005
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage (VDD ………………...-0.5 to +7.0V
)
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
1
Name
PD
Description
Power down pin
2
3
4
5
6
7
8
TP
Connected to ground
Common
Y Channel Duty Cycle Output
X Channel Duty Cycle Output
Do Not Connect
THEORY OF OPERATION
COM
Yout
Xout
NC
NC
VDD
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.
Do Not Connect
2.7V to 3.6 V
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.
Ordering Guide
Model
PWM
Frequency
Temperatur
e Range
Package
100Hz
MXD6125QB
LCC8, Pb-free
-40 to 105°C
All parts are shipped in tape and reel packaging.
Caution: ESD (electrostatic discharge) sensitive device.
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.
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).
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.
MEMSIC MXD6125Q
Page 3 of 6
2/24/2005
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).
DIGITAL INTERFACE
The MXD6125Q is easily interfaced with low cost
microcontrollers. For the digital output accelerometer, one
digital input port is required to read one accelerometer
output. For the analog output accelerometer, many low cost
microcontrollers are available today that feature integrated
A/D (analog to digital converters) with resolutions ranging
from 8 to 12 bits.
In many applications the microcontroller provides an
effective approach for the temperature compensation of the
sensitivity and the zero g offset. Specific code set, reference
designs, and applications notes are available from the
factory. The following parameters must be considered in a
digital interface:
Resolution: smallest detectable change in input acceleration
Bandwidth: detectable accelerations in a given period of
time
Acquisition Time: the duration of the measurement of the
acceleration signal
Figure 2: Accelerometer Position Relative to Gravity
X-Axis
Y-Axis
X-Axis
Orientation
To Earth’s
Change
Change
DUTY CYCLE DEFINITION
X Output per deg. Y Output per deg.
The MXD6125Q has two PWM duty cycle outputs (x,y).
The acceleration is proportional to the ratio T1/T2. The
zero g output is set to 50% duty cycle and the sensitivity
scale factor is set to 12.5% duty cycle change per g. These
nominal values are affected by the initial tolerance of the
device including zero g offset error and sensitivity error.
This device is offered from the factory programmed to
either a 10ms period (100 Hz).
Surface
(deg.)
90
(g)
of tilt
(mg)
0.15
1.37
2.88
(g)
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
1.000
0.996
0.985
0.940
0.866
0.707
0.500
0.342
0.174
0.087
0.000
0.000
0.087
0.174
0.342
0.500
0.707
0.866
0.940
0.985
0.996
1.000
85
80
70
60
45
30
20
10
5.86
8.59
12.23
15.04
16.35
17.16
17.37
17.45
T1
Length of the “on” portion of the cycle.
Length of the total cycle.
Ratio of the “0n” time (T1) of the cycle to
the total cycle (T2). Defined as T1/T2.
Time period of the “on” pulse. Defined as
T1.
T2 (Period)
Duty Cycle
5
0
Table 1: Changes in Tilt for X- and Y-Axes
Pulse width
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:
T2
T1
A (g)= (T1/T2 - 0.5)/12.5%
0g = 50% Duty Cycle
T2=10ms (factory programmable)
Figure 3: Typical output Duty C ycle
CHOOSING T2 AND COUNTER FREQUENCY
DESIGN TRADE-OFFS
Noise (mg rms) = Noise(mg/ Hz ) *
(Bandwidth(Hz)*1.6)
The noise level is one determinant of accelerometer
resolution. The second relates to the measurement
resolution of the counter when decoding the duty cycle
output. The actual resolution of the acceleration signal is
The peak-to-peak noise is approximately equal to 6.6 times
the rms value (for an average uncertainty of 0.1%).
MEMSIC MXD6125Q
Page 4 of 6
2/24/2005
limited by the time resolution of the counting devices used
to decode the duty cycle. The faster the counter clock, the
higher the resolution of the duty cycle and the shorter the
T2 period can be for a given resolution. Table 2 shows
some of the trade-offs. It is important to note that this is the
resolution due to the microprocessors’ counter. It is
probable that the accelerometer’s noise floor may set the
lower limit on the resolution.
When the part does 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.
POWER SUPPLY NOISE REJECTION
One capacitor is recommended for best rejection of power
supply noise (reference Figure 5 below). The capacitor
should be located as close as possible to the device supply
pin (VDD). 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.
Counter-
MEMSIC
Sample
Rate
Clock
Rate
(MHz)
2.0
1.0
0.5
Counts
Per T2
Cycle
20000
10000
5000
Reso-
lution
(mg)
0.4
0.8
1.6
Counts
per g
2500
1250
625
T2 (ms)
10.0
10.0
100
100
100
10.0
Table 2: Trade-Offs Between Microcontroller Counter Rate and
T2 Period.
MXD6125Q PIN DESCRIPTIONS
VDD – 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.
PCB LAYOUT AND FABRICATION SUGGESTIONS
TP– This pin should be connected to ground.
Xout – This pin is the digital output of the X-axis
acceleration sensor. It is factory programmable to 100Hz.
The user should ensure the load impedance is sufficiently
high as to not source/sink >100µA typical. 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.
1. Liberal use of ceramic bypass capacitors is
recommended. It is best to solder a 0.1uF capacitor
directly across VDD and COM pin.
2. Robust low inductance ground wiring should be used.
3. 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.
4. 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.
5. Vias can be added symmetrically around the ground
plane. Vias increase thermal isolation of the device
from the rest of the PCB.
Yout – This pin is the digital output of the Y-axis
acceleration sensor. It is factory programmable to 100Hz.
The user should ensure the load impedance is sufficiently
high as to not source/sink >100µA typical. 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 – Pin1 is the power down control pin. Pull this pin
HIGH will put the accelerometer into power down mode.
MEMSIC MXD6125Q
Page 5 of 6
2/24/2005
LCC-8 PACKAGE DRAWING
Hermetically Sealed Package Outline
MEMSIC MXD6125Q
Page 6 of 6
2/24/2005
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