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ADXRS646 Datasheet(PDF) 10 Page - Analog Devices
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ADXRS646 Datasheet(HTML) 10 Page - Analog Devices
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Rev. 0 | Page 10 of 12
The null output voltage (RATEOUT), sensitivity, self-test
responses (ST1 and ST2), and temperature output (TEMP)
of the ADXRS646 are ratiometric to V
. Therefore, using
the ADXRS646 with a supply-ratiometric ADC results in self-
cancellation of errors resulting from minor supply variations.
There remains a small, usually negligible, error due to non-
ratiometric behavior. Note that, to guarantee full measurement
should not be greater than AV
The nominal 3.0 V null output voltage is true for a symmetrical
swing range at RATEOUT (1B, 2A). However, an asymmetric
output swing may be suitable in some applications. Null adjust-
ment is possible by injecting a suitable current to SUMJ (1C, 2C).
Note that supply disturbances may cause some null instability.
Digital supply noise should be avoided, particularly in this case.
The ADXRS646 includes a self-test feature that actuates each
of the sensing structures and associated electronics in the same
manner as if the gyroscope were subjected to angular rate.
Self-test is activated by applying the standard logic high level ST1
pin (5F, 5G), the ST2 pin (4F, 4G), or both. Applying a logic high
to Pin ST1 causes the voltage at RATEOUT to change by −450 mV
(typical), and applying a logic high to Pin ST2 causes an opposite
change of +450 mV (typical). The voltage applied to the ST1 and
ST2 pins must never be greater than AV
. The self-test response
follows the temperature dependence of the viscosity of the
package atmosphere, approximately 0.25%/°C.
Activating both ST1 and ST2 simultaneously is not damaging.
The output responses generated by ST1 and ST2 are closely
matched (±2%), but actuating both simultaneously may result
in a small apparent null bias shift proportional to the degree of
The on-chip integration of the ADXRS646, as well as the
mature process with which it is manufactured, have provided
the gyroscope with field-proven reliability.
As an additional failure detection measure, self-test can be
performed at power-up or occasionally during operation. However,
some applications may require continuous self-test while sensing
rotation rate. Details outlining continuous self-test techniques
are available in the AN-768 Application Note, Using the
ADXRS150/ADXRS300 in Continuous Self-Test Mode. Although
the title of this application note refers to other Analog Devices
gyroscopes, the techniques apply equally to the ADXRS646.
MODIFYING THE MEASUREMENT RANGE
The ADXRS646 scale factor can be reduced to extend the
measurement range to as much as ±450°/sec by adding a
single 225 kΩ resistor between RATEOUT and SUMJ. If
an external resistor is added between RATEOUT and SUMJ,
must be proportionally increased to maintain correct
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