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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 25C. 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 -40C to +85C 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.
(c)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
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MXA6500E SPECIFICATIONS (Measurements @ 25C, Acceleration = 0 g unless otherwise noted; VDD = 3.0V unless otherwise
specified) MXA6500E Parameter SENSOR INPUT Measurement Range1 Nonlinearity Alignment Error2 Alignment Error Cross Axis Sensitivity3 SENSITIVITY Sensitivity, Sensitivity Change over Temperature4 ZERO g BIAS LEVEL 0 g Offset 0 g Offset 0 g Offset vs. Temperature4 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 Time5 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 VDD = 3.0V Delta from 25C at -40C Delta from 25C at +85C Each Axis VDD = 3.0V Delta from 25C @25C 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.
4 Defined as the output change from ambient to maximum temperature or ambient to minimum temperature. 5 Output settled to within 17mg.
MEMSIC MXA6500E Rev.B
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ABSOLUTE MAXIMUM RATINGS* .....................-0.5 to +7.0V Supply Voltage (VDD) Storage Temperature ......................-65C to +150C 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 VDD 2.7V to 3.6V Ordering Guide Model Package Style LCC8 MXA6500EP RoHS compliant LCC8, Pb-free MXA6500EB
Temperature Range -40 to 85C -40 to 85C
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
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Sensitivity (normalized)
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. 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 >100A. 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 0C to +50C 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 (-40C to +85C) 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 >100A. 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): Si x Ti3.40 = Sf x Tf3.40 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.
MEMSIC MXA6500E Rev.B
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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 (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 F.
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 VDD 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
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LCC-8 LOW PROFILE PACKAGE DRAWING
Hermetically Sealed Package Outline
MEMSIC MXA6500E Rev.B
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3/22/2005

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