Datasheet ADXL103, ADXL203 (Analog Devices) - 15

Data Sheet ADXL103/ADXL203 USING THE ADXL103/ ADXL203 W ITH OPERATING USING THE ADXL203 AS A DUAL-AXIS TILT SENSOR VOLTAGES OTHER THAN 5 V
One of the most popular applications of the ADXL203 is tilt The ADXL103/ADXL203 is tested and specified at VS = 5 V; measurement. An accelerometer uses the force of gravity as an however, it can be powered with VS as low as 3 V or as high input vector to determine the orientation of an object in space. as 6 V. Some performance parameters change as the supply An accelerometer is most sensitive to tilt when its sensitive axis voltage is varied. is perpendicular to the force of gravity, that is, parallel to the The ADXL103/ADXL203 output is ratiometric, so the output earth’s surface. At this orientation, its sensitivity to changes in sensitivity (or scale factor) varies proportional y to the supply tilt is highest. When the accelerometer is oriented on axis to voltage. At VS = 3 V, the output sensitivity is typical y 560 mV/g. gravity, that is, near its +1 g or –1 g reading, the change in The zero g bias output is also ratiometric, so the zero g output is output acceleration per degree of tilt is negligible. When the nominal y equal to V accelerometer is perpendicular to gravity, its output changes S/2 at all supply voltages. nearly 17.5 mg per degree of tilt. At 45°, its output changes at The output noise is not ratiometric but is absolute in volts; only 12.2 mg per degree, and resolution declines. therefore, the noise density decreases as the supply voltage increases. This is because the scale factor (mV/g) increases
Dual-Axis Tilt Sensor: Converting Acceleration to Tilt
while the noise voltage remains constant. At VS = 3 V, the When the accelerometer is oriented so both its x-axis and y-axis noise density is typically 190 µg/√Hz. are parallel to the earth’s surface, it can be used as a 2-axis tilt sensor Self test response in g is roughly proportional to the square of with a roll axis and a pitch axis. Once the output signal from the the supply voltage. However, when ratiometricity of sensitivity accelerometer has been converted to an acceleration that varies is factored in with supply voltage, self test response in volts is between –1 g and +1 g, the output tilt in degrees is calculated as roughly proportional to the cube of the supply voltage. So at PITCH = ASIN(AX/1 g) VS = 3 V, the self test response is approximately equivalent to ROLL = ASIN(AY/1 g) 150 mV or equivalent to 270 mg (typical). Be sure to account for overranges. It is possible for the The supply current decreases as the supply voltage decreases. accelerometers to output a signal greater than ±1 g due to Typical current consumption at VDD = 3 V is 450 µA. vibration, shock, or other accelerations. Rev. E | Page 15 of 16 Document Outline Features Applications General Description Functional Block Diagrams Revision History Specifications Absolute Maximum Ratings ESD Caution Pin Configurations and Function Descriptions Typical Performance Characteristics ADXL103 and ADXL203 AD22293 AD22035 and AD22037 All Models Theory of Operation Performance Applications Information Power Supply Decoupling Setting the Bandwidth Using CX and CY Self Test Design Trade-Offs for Selecting Filter Characteristics: The Noise/Bandwidth Trade-Off Using the ADXL103/ADXL203 with Operating Voltages Other than 5 V Using the ADXL203 as a Dual-Axis Tilt Sensor Dual-Axis Tilt Sensor: Converting Acceleration to Tilt Outline Dimensions Ordering Guide Automotive Products