MEMSIC MXD2020GL/HL MXD2020ML/NL
Contents
1. Each Axis Each Axis Based on 20 g 3 0V 5 0V supply Source 5 0V Supply output rails to supply voltage 3 0V Supply output rails to supply voltage S5 0V Supply 3 0V Supply Source or sink 3 0V 5 0V supply 3 0 to 5 0V supply S5 0V Supply 3 0V Supply Guaranteed by measurement of initial offset and sensitivity gt Alignment error is specified as the angle between the true and indicated axis of sensitivity gt Transverse sensitivity is the algebraic sum of the alignment and the inherent sensitivity errors 4 The device operates over a 3 0V to 5 25V supply range Please note that sensitivity and zero g bias level will be slightly different at 3 0V operation For devices to be operated at 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 MEMSIC MXD2020GL ML NL HL Page 2 of 7 MXD2020G HL Typ MXD2020M NL Typ of FS degrees duty cycle g 70 40 105 C level specifications on this page will be met Please contact the factory for specially trimmed devices for low supply voltage operation 2002 08 29 1 ABSOLUTE MAXIMUM RATINGS Supply Voltage Vpp Vpa ceseeeeeeeeees 0 5 to 7 0V Storage Temperature eee 65 C to 150 C Acceleration ccccecece eee ee ences ee eaenaenaes 50 000 g Stresses above those listed under Absolute Maxi2. 5 18 M XD 2020G LMA MEMS gt Improved Ultra Low Noise 1 g Dual Axis Accelerometer with Digital Outputs MXD2020GL HL MXD2020ML NL FEATURES Resolution better than 1 milli g Dual axis accelerometer fabricated on a monolithic CMOS IC On chip mixed mode signal processing No moving parts 50 000 g shock survival rating 17 Hz bandwidth expandable to gt 160 Hz 3 0V to 5 25V single supply continuous operation Continuous self test Independent axis programmability special order Compensated for Sensitivity over temperature Ultra low initial Zero g Offset APPLICATIONS Automotive Vehicle Security Vehicle stability control Headlight Angle Control Tilt Sensing Security Gas Line Elevator Fatigue Sensing Information Appliances Computer Peripherals PDA s Mouse Smart Pens Cell Phones Gaming Joystick RF Interface Menu Selection Tilt Sensing GPS electronic Compass tilt Correction Consumer LCD projectors pedometers blood pressure Monitor digital cameras GENERAL DESCRIPTION The MXD2020GL HL ML NL is a 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 MXD2020GL HL ML NL measures acceleration with a full scale range of 1 g and a sensitivity of 20 g It can measure both dynamic acceleration e g vibration and static acceleration e g gravity The MXD2020GL HL ML NL design is based
3. deg 90 17 45 85 17 37 80 17 16 70 16 35 60 15 04 45 12 23 30 8 59 20 5 86 10 2 88 5 1 37 0 0 15 Table 1 Changes in Tilt for X and Y Axes 2002 08 29 1 Pulse width Time period of the on pulse Defined as Tl Resolution The accelerometer resolution is limited by noise The output noise will vary with the measurement 9 bandwidth With the reduction of the bandwidth by a gt applying an external low pass filter the output noise drops Reduction of bandwidth will improve the signal to noise PE ratio and the resolution The output noise scales directly 1 with the square root of the measurement bandwidth The maximum amplitude of the noise its peak to peak value A T1 T2 0 5 20 approximately defines the worst case resolution of the 0g 50 Duty Cycle measurement With a simple RC low pass filter the rms T2 2 5ms or 10ms factory programmable noise is calculated as follows Figure 3 Typical output Duty C ycle Noise mg rms Noise mg V Hz Bandwidth H2 1 6 CHOOSING T2 AND COUNTER FREQUENCY DESIGN TRADE OFFS 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 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 shor
4. 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 rate and lower loss due to handling during assembly 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 MXD2020GL ML Page of 7 Sck Internal Temperature Tout optional y oe Oscillator Sensor ai ne Voltage A CLK Reference Vref y Continous Heater Self Test Control le o Px X axis gt LPF A D gt Dout X Factory Adjust Offset amp Gain g 4 x vy Y axis gt H LPF A D H p gt Dout Y 2 AXIS a SENSOR _ i A Vdd Gnd Vda MXD2020GL HL ML NL FUNCTIONAL BLOCK DIAGRAM The MXD2020GL HL ML NL provides two digital outputs that are set to 50 duty cycle at zero g acceleration The outputs are digital with duty cycles ratio of pulse width to period that are proportional to acceleration The duty cycle outputs can be directly interfaced to a micro proce
5. DIGITAL OUTPUT TO AN ANALOG OUTPUT The PWM output can be easily converted into an analog output by integration A simple RC filter can do the conversion Note that that the impedance of the circuit following the integrator must be much higher than the impedance of the RC filter Reference figure 4 for an example DOUT AOUT MEMSIC Accel Figure 4 Converting the digital output to an analog voltage POWER SUPPLY NOISE REJECTION Two capacitors and a resistor are recommended for best rejection of power supply noise reference Figure 5 below The capacitors should be located as close as possible to the device supply pins Vpa Vpp 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 uF and the resistor R can be 10 Q 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 Cl C2 0 47 uF and R 270 Q will virtually eliminate power supply noise effects MEMSIC MXD2020GL ML NL HL Page 6 of 7 V SUPPLY VDA VDD MEMSIC Accelerometer Figure 5 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 3 Robust low inductance ground wiring should be u
6. TTERY OPERATION DUTY CYCLE DEFINITION In applications with power limitations power cycling can The MXD2020GL HL ML NL has two PWM duty cycle be used to extend the battery operating life One important outputs x y The acceleration is proportional to the ratio consideration when power cycling is that the accelerometer T1 T2 The zero g output is set to 50 duty cycle and the turn on time limits the frequency bandwidth of the sensitivity scale factor is set to 20 duty cycle change per accelerations to be measured For example operating at g These nominal values are affected by the initial 3 0V the turn on time is 40mS To double the operating tolerance of the device including zero g offset error and time a particular application may cycle power ON for sensitivity error This device is offered from the factory 40mS then OFF for 40mS resulting in a measurement programmed to either a 10ms period 100 Hz or a 2 5ms period of 80mS or a frequency of 12 5Hz With a period 400Hz frequency of measurements of 12 5Hz accelerations changes as high as 6 25Hz can be detected Power cycling Tl Length of the on portion of the cycle can be used effectively in many inclinometry applications T2 Period Length of the total cycle where inclination changes can be slow and infrequent Duty Cycle Ratio of the On time T1 of the cycle to the total cycle T2 Defined as T1 T2 MEMSIC MXD2020GL ML NL HL Page 5 of 7 2002 08 29 1 CONVERTING THE
7. ction 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 MEMSIC MXD2020GL ML NL HL Page 3 of 7 2002 08 29 1 MXD2020GL HL ML NL PIN DESCRIPTIONS Vpp This is the supply input for the digital circuits and the sensor heater in the accelerometer The DC voltage should be between 3 0 and 5 25 volts Refer to the section on PCB layout and fabrication suggestions for guidance on external parts and connections recommended Vpa This is the power supply input for the analog amplifiers in the accelerometer Vp should always be connected to Vpp Refer to the section on PCB layout and fabrication suggestions for guidance on external parts and connections recommended Gnd This is the ground pin for the accelerometer Dourx This
8. mum 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 O ON 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 Ordering Guide A single heat source centered in the silicon chip is Model Package Digital Temperature pue peoed ine cavity Equally speed aluminum polysilicon thermopiles groups of Style Output Range oye LCC 8 thermocouples are located equidistantly on all four sides of 100 Hz 0 to 70 C the heat source dual axis Under zero acceleration a LCC 8 400Hz 0 to 70 C temperature gradient is symmetrical about the heat source LCC 8 so that the temperature is the same at all four thermopiles mxp2020m LCC 8 100 Hz 40 to 105 causing them to output the same voltage LCC 8 400 Hz 40 to 105 All parts are shipped in tape and reel packaging Caution ESD electrostatic discharge sensitive device Acceleration in any dire
9. pin is the digital output of the x axis acceleration sensor It is factory programmable to 100 Hz or 400 Hz The user should ensure the load impedance is sufficiently high as to not source sink gt 100pA 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 Douty This pin is the digital output of the y axis acceleration sensor It is factory programmable to 100 Hz or 400 Hz The user should ensure the load impedance is sufficiently high as to not source sink gt 100pA 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 Tour This pin is the buffered output of the temperature sensor The analog voltage at Tour 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 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
10. sed 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 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 2002 08 29 1 LCC 8 PACKAGE DRAWING Fig 6 Hermetically Sealed Package Outline MEMSIC MXD2020GL ML NL HL Page 7 of 7 2002 08 29 1
11. signal between 400kHz And 1 6MHz Vier A reference voltage is available from this pin It is set at 2 50V typical and has 100uA of drive capability MEMSIC MXD2020GL ML NL HL Page 4 of 7 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 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 OOMX 007 gravity Top View Figure 2 Accelerometer Position Relative to Gravity Y Axis X Axis Orientatio Change n X Output Y Output per deg To Earth s g of tilt Surface mg
12. ssor The typical noise floor is 0 2 mg VHz allowing signals below 1 milli g to be resolved at 1 Hz bandwidth The MXD2020GL HL ML NL is packaged in a hermetically sealed LCC surface mount package 5 mm x 5 mm x 2 mm height and is operational over a 40 C to 105 C M NL and 0 C to 70 C G HL temperature range MEMSIC Inc 800 Turnpike St Suite 202 North Andover MA 01845 Tel 978 738 0900 Fax 978 738 0196 www memsic com 2002 08 29 1 MXD2020GL HL ML NL SPECIFICATIONS Measurements 25 C Acceleration 0 g unless otherwise noted Vpp Vpa 5 0V Min Each Axis unless otherwise specified Parameter SENSOR INPUT Measurement Range Nonlinearity Alignment Error Transverse Sensitivity SENSITIVITY Sensitivity Digital Outputs at pins Dourtx and Doury Change over Temperature ZERO g BIAS LEVEL 0 g Offset 0 g Duty Cycle 0 g Offset over Temperature NOISE PERFORMANCE Noise Density rms FREQUENCY RESPONSE 3dB Bandwidth TEMPERATURE OUTPUT Tout Voltage Sensitivity VOLTAGE REFERENCE Vref Change over Temperature Current Drive Capability SELF TEST Continuous Voltage at Dourx Doury under Failure Continuous Voltage at Dourx Doury under Failure Doutx and Douty OUTPUTS Normal Output Range Current Rise Fall Time Turn On Time POWER SUPPLY Operating Voltage Range Supply Current Supply Current TEMPERATURE RANGE Operating Range NOTES Best fit straight line X Sensor to Y Sensor
13. ter the T2 period can be for a given resolution Table 2 shows some of the trade offs Itis 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 The peak to peak noise is approximately equal to 6 6 times the rms value for an average uncertainty of 0 1 DIGITAL INTERFACE The MXD2020GL HL ML NL 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 Counter effective approach for the temperature compensation of the MEMSIC P sensitivity and the zero g offset Specific code set reference Sample Rate designs and applications notes are available from the T2 ms Rate 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 Table 2 Trade Offs Between Microcontroller Counter Rate and acceleration signal T2 Period USING THE ACCELEROMETER IN VERY LOW POWER APPLICATIONS BA
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