Datasheet ADXL1005 (Analog Devices) - 10

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ADXL1005 Data Sheet APPLICATIONS INFORMATION APPLICATION CIRCUIT
4. Subtract the two readings and compare the result to the For most applications, a single 1 μF capacitor adequately expected value from Table 1, while factoring in the decouples the accelerometer from noise on the power supply. A response curve due to supply voltage, if necessary, from band limiting filter at the output provides suppression of out of Figure 21. band noise and signal. A capacitive load between 100 pF and The self test function can be activated at any point during 22 nF is recommended. normal operation by setting the ST pin to VDD. Self test takes The output amplifier can drive resistive loads up to 2 mA of approximately 300 μs from the assertion of the ST pin to a source current, for example a load greater than 2.5 kΩ for 5 V result. Acceleration outputs return approximately 300 μs after operation. If the output is to drive a capacitive load greater than the release of the ST pin. While performing the self test or equal to 100 pF, a series resistor of at least 8 kΩ is required to measurement, do not use the accelerometer output to measure maintain the amplifier stability. external acceleration.
0.8
When inactive, the ST and STANDBY pins are forced low. The
MAXIMUM
overrange indicator is an output that can be monitored to
0.7 TYPICAL MINIMUM
identify the status of the system.
0.6 OPTIONAL LOW-PASS FILTER (mV) 0.5 R LTA V E OUT D 0.4 C EST T 0.3 F V L SS SE 0.2 32 31 30 29 28 27 26 25 0.1 1 24 2 23 0
1
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2
02
3 22 SUPPLY VOLTAGE (V)
16589-
4 21
Figure 21. Typical Self Test Delta vs. Supply Voltage
ADXL1005 5 20 OR RATIOMETRIC OUTPUT VOLTAGE 6 19
The ADXL1005 was tested and specified at VDD = 5.0 V. However,
7 18
the ADXL1005 can be powered with VDD as low as 3.0 V or as high
8 17
as 5.25 V. Some performance parameters change as the supply
9 10 11 12 13 14 15 16
voltage is varied.
VDD (3.0V TO 5.25V
The ADXL1005 output is ratiometric to the supply voltage, VDD.
1µF ST (ACTIVE HIGH) SUPPLY VOLTAGE)
007 Therefore, the output sensitivity (or scale factor) varies propor-
STANDBY (ACTIVE HIGH)
16589- tionally to the supply voltage. At VDD = 5.0 V, the output sensitivity Figure 20. Application Circuit is typically 20 mV/g for the ADXL1005. The zero g bias output
ON DEMAND SELF TEST
is ratiometric also and is nominally midscale relative to the supply voltage (VDD/2). A fully integrated electromechanical self test function is designed
22
into the ADXL1005. This function electrostatically actuates the accelerometer proof mass, resulting in a displacement of the
20
capacitive sense fingers. This displacement is equivalent to the displacement that occurs as a result of external acceleration input.
) g 18
The proof mass displacement is processed by the same signal
(mV/
processing circuitry as a true acceleration output signal,
Y T 16 IVI
providing complete coverage of both the electrical and mechanical
T
responses of the sensor system.
14 SENSI
The self test feature can be exercised by the user with the following steps:
12
1. Measure the output voltage.
10
2. Turn on self test by setting the ST pin to V
3.0 3.5 4.0 4.5 5.0
122 DD. 9-
SUPPLY VOLTAGE (V)
1658 3. Measure the output again. Figure 22. Sensitivity vs. Supply Voltage Rev. 0 | Page 10 of 14 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE RECOMMENDED SOLDERING PROFILE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION MECHANICAL DEVICE OPERATION OPERATING MODES Measure Mode Standby Mode BANDWIDTH APPLICATIONS INFORMATION APPLICATION CIRCUIT ON DEMAND SELF TEST RATIOMETRIC OUTPUT VOLTAGE INTERFACING ANALOG OUTPUT BELOW 10 kHz INTERFACING ANALOG OUTPUT BEYOND 10 kHz OVERRANGE MECHANICAL CONSIDERATIONS FOR MOUNTING LAYOUT AND DESIGN RECOMMENDATIONS OUTLINE DIMENSIONS ORDERING GUIDE