Improved Low Cost 5 g Dual-Axis Accelerometer with Ratiometric Analog Outputs MXR7305VF FEATURES z z z z z z z z z z z z z z Dual axis accelerometer fabricated on a single CMOS IC Monolithic design with mixed mode signal processing RoHS compliant On-chip sensitivity compensation for temperature variations On Demand Self Test 5g dynamic range, 250mV/g sensitivity Independent axis programmability (special order) Resolution better than 1mg Zero-g Output Temperature drift, better than 80mg over -40~95degC range 27Hz bandwidth >50,000 g shock survival rating 4.50V to 5.25V single supply operation Small surface mount package, 5mm x 5mm x 2mm Improved thermal gradient performance MXR7305V FUNCTIONAL BLOCK DIAGRAM APPLICATION Automotive - Roll over sensing, VSC/EPB application GENERAL DESCRIPTION The MXR7305VF is a low cost, dual axis accelerometer built on a standard, submicron CMOS process. It measures acceleration with a full-scale range of 5g and a sensitivity of 250mV/g. The MXR7305VF provides a g-proportional ratiometric analog output above/below the zero-g point at 50% of the supply voltage. (Ref. other MEMSIC data sheets for absolute analog or digital outputs). The typical noise floor is 0.6mg / Hz , allowing signals below 1mg to be resolved at 1Hz bandwidth. The 3dB rolloff of the device occurs at 27Hz. The MXR7305V is available in a low profile LCC surface mount package (5mm x 5mm 2mm). It is hermetically sealed and operational over a -40C to +95C 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 MXR7305V Rev.A Page 1 of 6 Memsic's accelerometer technology allows for designs from 1 g to 70 g with custom versions available above 70 g. It can measure both dynamic acceleration (e.g., vibration) and static acceleration (e.g., gravity). The design is based on heat convection and requires no solid proof mass. This eliminates stiction and particle problems associated with competitive devices and provide shock survival greater than 50,000 g, leading to significantly lower failure rates and lower loss due to handling during assembly and at customer field application. Due to the standard CMOS structure of the MXR7305V, additional circuitry can easily be incorporated into custom versions for high volume applications. Contact Memsic's local office for more information. (c)MEMSIC, Inc. One Technology Drive, Suite 325, Andover, MA01810, USA Tel: +1 978 738 0900 Fax: +1 978 738 0196 www.memsic.com 6/18/2009 MXR7305VF SPECIFICATIONS (Measurements @ 25C, Acceleration = 0 g unless otherwise noted; VDD = 5.0V unless otherwise specified) Parameter SENSOR INPUT Measurement Range1 No linearity Conditions Each Axis Min MXR7305V Typ 5.0 2.0 250 1.0 265 2.0 +3 +3 +4 +4 mV/g % % % % % 0.00 2.5 +0.20 2.55 1.0 80 40 120 80 60 50 g V % mg mg mg mg mg mg 0.6 1.5 mg/ Hz 24 27 -18 30 Hz deg -650 -700 -600 -600 -500 -600 4.0 -830 -850 -900 -1000 -1050 -1100 -1100 -1500 -1600 20 25 50 mV mV mV mV mV mV V V mS Kohms 0.5 Alignment Error2 Transverse Sensitivity3 SENSITIVITY Each Axis Sensitivity, Analog Outputs at pins Xout and Yout4 @5.0V supply Sensitivity Ratiometricity 5V+/-5% Change over Temperature 6 from 25C -40C to +95C Change over Temperature with 2nd Temp Comp6 Change over Temperature with aging Change over Temperature with 2nd Temp Comp and aging6,8 ZERO g BIAS LEVEL Each Axis 0 g Offset 0 g Voltage 0 g Offset Ratiometricity 5V+/-5% 0 g Offset over Temperature from 25C, based on 250mV/g With 2nd Temp Comp 0g Offset over Temp with aging6, from 25C, based on 250mV/g With 2nd Temp Comp 6,7 0g Offset over Temp max-min from -20C to +80C max-min from 0C to 60C NOISE PERFORMANCE -40C to +95C Noise Density, rms FREQUENCY RESPONSE 3dB Bandwidth Phase delay at 5Hz SELF TEST Delta Output changes at Xout, Yout at 25C, 0g input 0.2 0.5 Selftest Input Voltage Selftest Response Time Self Test Pin Pull-Down Resistor (Internal) Xout and Yout OUTPUTS Normal Output Range (Guaranteed symmetric clipping) Current Resistance Capacitance Turn-On Time POWER SUPPLY Operating Voltage Range Supply Current5 TEMPERATURE RANGE Operating Range PRESSURE RANGE Operating Range MEMSIC MXR7305VF Rev.A High Low 235 -6 -3 -6 -4 -0.20 2.45 -80 -40 -120 -80 0 0 0.5 1.0 30 V A 80 100 100 200 ohm pF mS 5.0 4.1 5.25 5.0 V mA -40 +95 C 40 300 KPa. @5.0V Supply Page 2 of 6 1.0 20 4.5 100 Source or sink, @ 4.5V-5.25V supply @ 5.0V RMS Units g % of FS mg degrees % Best fit straight line 1g input range, least squares fit at 25C, 1g input at 25C, -1g input -40C~95C, 0g input -40C~95C, 1g input -40C~95C, -1g input Max 4.5 3.2 6/18/2009 X=2.25V Y=2.50V NOTES 1 Guaranteed by measurement of initial offset and sensitivity. 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 device operates over a 4.5V to 5.25V supply range. The output zero g reference voltage scales 50% of the supply voltage. Sensitivity has a linear scale over the supply range of 4.5 to 5.25 volts according to the ratio (Vdd/5.0 volts) x (250mV/g). recommended to filter with a minimum of 200Hz low pass filter. 5 Note that the accelerometer has a constant heater power control circuit thereby requiring higher supply current at lower operating voltage 6 Based on characterization data of 3lotsx30 parts per lot 7 Calculated by MAX-MIN 8 Pending for qualification data 2 ABSOLUTE MAXIMUM RATINGS* Supply Voltage (VDD, VDA) ..................-0.5 to +7.0V Storage Temperature ......................-70C to +150C Storage Pressure.......................................1,378 kPa Acceleration (any axis, Un-powered for 0.5 msec)..50,000 g X=2.50V Y=2.75V X=2.50V Y=2.50V X=2.75V Y=2.50V EARTH'S SURFACE Note: Output Short Circuit Duration, any pin to common.......Indefinite *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. X=2.50V Y=2.25V TOP VIEW (Not to Scale) 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. Small circle indicates pin one (1). Pin Description: LCC-8 Package Exposure for up to 60 minutes to absolute maximum ratings for supply voltages will not affect device reliability. Package Characteristics Package JC JA LCC-8 110C/W 22C/W Ordering Guide Model MXR7305VF Device Weight < 1 gram Package Style LCC-8 SMD* Pin 1 2 Name STIN CLK 3 4 5 6 7 8 COM NC NC YOUT XOUT VDD Description Self -Test Input To be grounded. (Optional Serial Clock Input) Ground No Connect No Connect Y-Channel Ratiometric Output X-Channel Ratiometric Output Supply Voltage 4.5 to 5.25 V * Parts are shipped in tape and reel packaging. ESD Compliance: The MXR7305V sensor is in compliance with the following ESD standards: Human Body and 2500V per AEC-Q100-002 Rev. E Machine Model and 250V per AEC-Q100-003 Rev. E Caution ESD (electrostatic discharge) sensitive device. Mounting Orientation: The package orientation of the MXR7305V does not affect the performance of the sensor. The specifications as stated in page 2 remain the same. Thus, if the sensor is installed with one of its axis of sensitivity in the vertical plane, it detects accelerations in the Z-axis. MEMSIC MXR7305VF Rev.A Page 3 of 6 6/18/2009 THEORY OF OPERATION YOUT - (pin 6) Y-axis acceleration signal output. 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 except it is a gas in the MEMSIC sensor. It is capable of sinking or sourcing up to 100A. 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 MXR7305V can be programmed for non-equal sensitivities on the X- and Yaxes. Contact Memsic's local office for additional 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. 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 MXR7305V, one to measure acceleration in the x-axis and one to measure acceleration in the Y-axis. For more details visit the MEMSIC website at www.memsic.com for a picture/graphic description of the free convection heat transfer principle. NC - (pin 5, 4) No connect. These pins can be tied to common if the application does not allow pins to remain unconnected. COM - (pin 3) This is the ground pin for the MXR7305V CLK - (pin 2) This is an optional serial clock input. The standard product is delivered with an internal clock (1000 kHz. However, an external clock between 400 kHz and 1.6 MHz can be used as an option, if the sensor is programmed from the factory to run in external clock mode. This pin is grounded internally with a 50 Kohm resistor if an external clock is used it should be able to drive this load. But if external clock is not used, in order to minimize noise and ESD this pin should be grounded externally as well. ST IN- (pin 1) Self -Test Input This pin controls the self-test function of the sensor. Bringing STIN high will cause a negative deflection around 830mV to the Xout and Yout from the 0g value. PIN DESCRIPTIONS VDD - (pin 8). Supply voltage input for digital and analog circuits. For proper operation VDD must be between 4.50 and 5.25 volts. Refer to the section on PCB layout and fabrication suggestions for guidance on external parts and connections recommended. XOUT - (pin 7). X-axis acceleration signal output It is capable of sinking or sourcing up to 100A. 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 MXR7305V can be programmed for non-equal sensitivities on the x- and yaxes. Contact Memsic's local office for additional information. MEMSIC MXR7305VF Rev.A Page 4 of 6 AOUT Xout Y - AOUT Yout X Self Test 0 10 20 30 40 50 60 70 80 90 100110 Time - millisec 6/18/2009 sensitive to sensor structure defect and damage. As long as initial offset is within specification the sensor is functioning correctly. The sensor structure for the Thermal technology is guaranteed to fall outside the specified initial zero g offset parameters if the sensor is damaged or thermopile is failing. In most cases this will result in the output voltage hitting the rail at 5.0 volts. SELF-TEST DESCRIPTION When Self-test is enabled the sensitivity compensation is turned off (disabled). With the sensitivity compensation disabled, the sensitivity will change according to the equation below: Si x Ti2.8 = k x Sf x Tf2.8 ST OFF X=2.50V Y=2.50V PCB LAYOUT AND FABRICATION SUGGESTIONS Reference figure and the notes below for recommendations on connecting a power source to the MEMSIC device and PCB fabrication. ST ON X=1.70V Y=1.70V EARTH'S SURFACE 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 C, k is the ratio between uncompensated sensitivity and compensated sensitivity at 25C. Sensitivity (normalized) 2.5 2.0 1.5 1.0 0.5 PCB Layout 0.0 -40 -20 0 20 40 60 80 100 Temperature (C) Thermal Accelerometer Sensitivity MEMSIC . Accelerometer Position Relative to Gravity Note1: When the temperature compensation is disabled and self-test is enabled. Self-test follows different gas law from sensitivity temperature dependence. It changes much smaller than sensitivity; this is why the temperature compensation is not done on self-test conditions. Note2: Initial offset monitoring is a much better and reliable method to ensure sensor integrity, since it is ultra MEMSIC MXR7305VF Rev.A Page 5 of 6 Notes: 1. C1 = 1.0F 2. The capacitor should be located as close as possible to the device supply pin VDD, since the internal heater is in PWM (1MHz) control mode, with all VDD on the heater at some portion of the time, by using larger value capacitor can minimize the induced noise on the outputs. 3. The CLK is grounded internally with a 50 kOhm resistor, however, in order to minimize noise and ESD this pin should be grounded externally as well. 4. Robust low inductance ground wiring should be used. 5. Care should be taken (like isolated rings and planes, signal route out perpendicular to the external thermal gradient) to ensure there is "thermal symmetry" on the PCB immediately surrounding the MEMSIC device and that there is no significant heat source nearby since it may cause a temperature gradient ("thermal gradient") across MEMSIC device, thus result in performance change (additional initial offset and offset drift). 6/18/2009 MECHANICAL PACKAGE OUTLINE DIMENSIONS Dimensions shown in mm. LCC-8, Eight Pin, Hermetically Sealed, Surface Mount Package MEMSIC MXR7305VF Rev.A Page 6 of 6 6/18/2009