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Low Cost, ±10 g Dual Axis Accelerometer with Digital Outputs
MXD2002A/B
FEATURES
Sck (optional)
Internal O scillator
Tem perature Sensor
Voltage R eference
Tout
Dual axis accelerometer fabricated on a monolithic CMOS IC On-chip mixed mode signal processing Resolution better than 6 milli-g 50,000 g shock survival rating 30 Hz bandwidth 2.70V to 5.25V single supply operation Small (5mm x 5mm x 2mm) surface mount package Continuous self test Independently programmable axis (factory special)
C LK
Vref
H eater Control
C ontinous Self Test
X axis
LPF
A/D
D out X
Factory Adjust O ffset & G ain
APPLICATIONS
Automotive – Vehicle Security/Active Suspension/ABS HED Angle Control/Tilt Sensing Security – Gas Line/Elevator/Fatigue Sensing Office Equipment – Computer Peripherals/PDA’s/Mouse Smart Pens/Cell Phones Gaming – Joystick/RF Interface/Menu Selection/Tilt Sensing White Goods – Spin/Vibration Control
Y axis
LPF
A/D
D out Y
2-AX IS SENSO R
Vdd
Gnd
Vda
MXD2002A/B FUNCTIONAL BLOCK DIAGRAM
The MXD2002A/B is a very low cost, dual axis accelerometer fabricated on a standard, submicron CMOS process. The MXD2002A/B measures acceleration with a full-scale range of ±10 g. (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 MXD2002A/B 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 up to 50,000 g, leading to significantly lower failure rates and lower loss due to handling during assembly. The MXD2002A/B provides a digital output (ref. other MEMSIC data sheets for analog or ratiometric analog outputs). The outputs are digital signals with duty cycles (ratio of pulsewidth to period) that are proportional to acceleration. The duty cycle outputs can be directly interfaced to a micro-processor.
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.
The typical noise floor is .0015% duty cycle / Hz allowing signals below 6 milli-g to be resolved at 1 Hz bandwidth. The MXD2002A/B is available in a low profile LCC surface mount package (5mm x 5mm x 2mm height). It is hermetically sealed and operational over a -40°C to +105°C temperature range.
Due to the standard CMOS structure of the MXD2002A/B, additional circuitry can easily be incorporated into custom versions for high volume applications. Contact the factory for more information.
MEMSIC, Inc. 100 Burtt Road, Andover, MA 01810 Tel: 978.623.8188 Fax: 978.623.9945 www.memsic.com
MEMSIC MXD2002A/B Rev.E
Page 1 of 8
5/15/2004
MXD2002A/B SPECIFICATIONS (Measurements @ 25°C, Acceleration = 0 unless otherwise noted, VDD, VDA =
5.0V unless otherwise specified)
MXD2002A/B
Parameter SENSOR INPUT Measurement Range1 Nonlinearity Alignment Error2 Transverse Sensitivity3 SENSITIVITY DOUTX and DOUTY Change over Temperature (uncompensated)4 Change over Temperature (compensated) 4 ZERO g BIAS LEVEL 0 g Offset5 0 g Duty Cycle5 0 g Offset over Temperature NOISE PERFORMANCE Noise Density, % Duty Cycle FREQUENCY RESPONSE 3dB Bandwidth TEMPERATURE OUTPUT Tout Voltage Sensitivity VOLTAGE REFERENCE VRef Change over Temperature Current Drive Capability SELF TEST Continuous Voltage at DOUTX, DOUTY under Failure Continuous Voltage at DOUTX, DOUTY under Failure DOUTX and DOUTY OUTPUTS Normal Output Range Current Rise/Fall Time POWER SUPPLY Operating Voltage Range Supply Current Supply Current6,7 TEMPERATURE RANGE Operating Range NOTES
Conditions Each Axis Best fit straight line
Min ±10
Typ
Max
Units g % of FS degrees %
1.0 ±1.0 ±2.0 1.80 -47 <3.0 -0.70 48.6 0.00 50 ±2.0 ±004 .0015 2.00
2.0
Each Axis @5.0V supply ∆ from 25°C, at –40°C ∆ from 25°C, at +105°C ∆ from 25°C, –40°C to +105°C Each Axis ∆ from 25°C ∆ from 25°C, based on 2%/g
2.20 % Duty Cycle/g +93 % % % +0.70 g 51.4 % Duty Cycle mg/°C % / °C 0.005 % Duty Cycle/ Hz
30 1.15 4.6 @2.7V-5.0V supply Source @5.0V Supply, output rails to supply voltage @2.7V Supply, output rails to supply voltage Digital Signal of 100 Hz or 400Hz @5.0V Supply @2.7V Supply Source or sink, @ 2.7V-5.0V supply 2.7 to 5.0V Supply 2.4 1.25 5.0 2.5 0.1 1.35 5.4 2.65 100
Hz V mV/°K V mV/°C µA
5.0 2.7 0.1 0.1 90 100 100 4.9 2.6 110
V V V V µA nSec
@ 5.0V @ 2.7V
2.7 3.0 3.0 -40
4.2 5.4
5.25 4.9 6 +105
V mA mA °C
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 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.
2
1
5 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. 6 Note that the accelerometer has a constant heater power control circuit thereby displaying higher supply current at lower operating voltage.
MEMSIC MXD2002A/B Rev.E
Page 2 of 8
5/15/2004
ABSOLUTE MAXIMUM RATINGS* Supply Voltage (VDD, VDA) ………………...-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.
Caution ESD (electrostatic discharge) sensitive device. 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. 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. PIN DESCRIPTIONS VDD – 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. VDA – 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. Gnd – This is the ground pin for the accelerometer. DOUTX – This 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 >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.
DOUTY – This pin is the digital output of the y-axis
Package Characteristics Package θJA θJC LCC-8 110°C/W 22°C/W
8 1 2 3 M E M S IC 7
Device Weight < 1 gram
X +g 6 5
4 Y +g Top View
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. Small circle indicates pin one(1).
Pin Description: LCC-8 Package Pin Name Description 1 TOUT Temperature (Analog Voltage) 2 DOUTY Y-Axis Acceleration Digital Signal 3 Gnd Ground 4 VDA Analog Supply Voltage 5 DOUTX X-Axis Acceleration Digital Signal 6 Vref 2.5V Reference 7 Sck Optional External Clock 8 VDD Digital Supply Voltage
Ordering Guide Model Package Style D2002AL D2002BL LCC-8 SMD* LCC-8 SMD*
Digital Output 100 Hz 400 Hz
*LCC parts are shipped in tape and reel packagin
