ADXRS646 Analog Devices, Inc., ADXRS646 Datasheet - Page 8

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ADXRS646

Manufacturer Part Number
ADXRS646
Description
High Stability, Low Noise Vibration Rejecting Yaw Rate Gyro
Manufacturer
Analog Devices, Inc.
Datasheet

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ADXRS646
The voltage at TEMP (3F, 3G) is nominally 2.9 V at 25°C, and
V
Although the TEMP output is highly repeatable, it has only
modest absolute accuracy.
SUPPLY RATIOMETRICITY
The AD646’s RATEOUT, ST1, ST2, and TEMP signals are
ratiometric to the V
sensitivity, and temperature outputs are proportional to V
So, it is most easily used with a supply-ratiometric ADC which
results in self cancellation of errors due to minor supply
variations. There is some small, usually negligible, error due to
non-ratiometric behavior. Note that, in order to guarantee full
rate range, V
The nominal 3.0 V null is for a symmetrical swing range at
RATEOUT (1B, 2A). However, a nonsymmetric output swing
may be suitable in some applications. Null adjustment is possible
by injecting a suitable current to SUMJ (1C, 2C). Note that supply
disturbances may reflect some null instability. Digital supply noise
should be avoided, particularly in this case.
SELF-TEST FUNCTION
The ADXRS646 includes a self-test feature that actuates each of
the sensing structures and associated electronics in the same
manner, as if subjected to angular rate. It is activated by standard
logic high levels applied to Input ST1 (5F, 5G), Input ST2
(4F, 4G), or both. ST1 causes the voltage at RATEOUT to change
about −0.5 V, and ST2 causes an opposite change of +0.5 V. The
self-test response follows the viscosity temperature dependence
of the package atmosphere, approximately 0.25%/°C.
Activating both ST1 and ST2 simultaneously is not damaging.
ST1 and ST2 are fairly closely matched (±2%), but actuating
both simultaneously may result in a small apparent null bias
shift proportional to the degree of self-test mismatch.
ST1 and ST2 are activated by applying a voltage equal to V
to the ST1 pin and the ST2 pin. The voltage applied to ST1 and
ST2 must never be greater than AV
CONTINUOUS SELF-TEST
The on-chip integration of the ADXRS646 gives it higher reliability
than is obtainable with any other high volume manufacturing
method. Also, it is manufactured under a mature BiMOS process
that has field-proven reliability. As an additional failure detection
measure, power-on self-test can be performed. However, some
applications may warrant continuous self-test while sensing rate.
Details outlining continuous self-test techniques are also
available in the
NULL ADJUSTMENT
RATIO
= 6 V. The temperature coefficient is ~10 mV/°C at 25°C.
RATIO
Figure 12. Temperature Sensor Structure
AN-768
should not be greater than AV
V
RATIO
RATIO
R
FIXED
Application Note.
voltage, i.e., the null voltage, rate
R
TEMP
CC
.
V
TEMP
CC
RATIO
RATIO
Rev. PrA | Page 8 of 12
.
MODIFYING THE MEASUREMENT RANGE
The ADXRS646 scale factor can be reduced to extend the
measurement range to as much as ±450°/s by adding a single
225kΩ resistor between the RATEOUT and SUMJ. If an
external resistor is added between RATEOUT and SUMJ C
must be proportionally increased to maintain correct
bandwidth.
The ADXRS646 excellent vibration rejection is demonstrated in
the graphs below. Figure 13 shows the ADXRS646 output
response with and without 15g RMS 50Hz to 5kHz of random
vibration. Bandwidth of the gyro was limited to 1600Hz.
Performance is similar regardless of the direction of input
vibration.
Figure 14 demonstrates the ADXRS646 DC bias response to 5g
Sine vibration over the 20Hz to 5kHz range. As can be seen,
there are no sensitive frequencies present and vibration
rectification is vanishingly small. As in the previous example
gyro bandwidth was set to 1600Hz.
Figure 13. ADXRS646 Output Response With and Without Random Vibration
MECHANICAL PERFORMANCE
Figure 14. ADXRS646 Sine Vibration Output Response (5g, 20Hz to 5kHz)
‐0.02
‐0.04
0.00001
0.12
0.08
0.06
0.04
0.02
0.0001
0.1
0.001
0.01
0
0.1
10
1
10
Preliminary Technical Data
(15g RMS, 50Hz to 5kHz)
100
100
Frequency
Hz
1000
1000
10000
OUT
10000

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