Data Sheet ADXRS642
Rev. A | Page 9 of 12
MODIFYING THE MEASUREMENT RANGE
The ADXRS642 scale factor can be reduced to extend the
measurement range to as much as ±450°/sec by adding a single
225 kΩ resistor between the RATEOUT and SUMJ. If an external
resistor is added between RATEOUT and SUMJ, C
OUT
must be
proportionally reduced to maintain the correct bandwidth.
NULL ADJUSTMENT
The nominal 2.5 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 ADXRS642 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 −0.3 V, and ST2 causes an opposite change of +0.3 V. T h e
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
RATIO
to the ST1 pin and the ST2 pin. The voltage applied to ST1 and
ST2 must never be greater than AV
CC
.
CONTINUOUS SELF-TEST
The on-chip integration of the ADXRS642 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 AN-768 Application Note.
MECHANICAL PERFORMANCE
The ADXRS642 excellent vibration rejection is demonstrated in
Figure 15 and Figure 16. Figure 15 shows the ADXRS642 output
response with and without 15 g rms 50 Hz to 5 kHz of random
vibration. The bandwidth of the gyro was limited to 1600 Hz.
Performance is similar regardless of the direction of the input
vibration.
0.00001
0.0001
0.001
0.01
0.1
1
(°/s)
2
/√Hz
10 100 1k
FREQUENCY (Hz)
10k
09770-014
Figure 15. ADXRS642 Output Response with and Without Random Vibration
(15 g rms, 50 Hz to 5 kHz)
Figure 16 demonstrates the ADXRS642 dc noise response to 5g
sine vibration over the 20 Hz to 5 kHz range. As can be seen,
there are no sensitive frequencies present, and vibration
rectification is vanishingly small. As in the previous example,
the gyro bandwidth was set to 1600 Hz.
09770-015
–0.04
–0.02
0
0.02
0.04
0.06
0.08
0.10
0.12
10 100 1k 10k
FREQUENCY (Hz)
(°/s)
Figure 16. ADXRS642 Sine Vibration Noise Response (5 g, 20 Hz to 5 kHz)
