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ADXRS612
ADXRS612 AND SUPPLY RATIOMETRICITY
The ADXRS612 RATEOUT and TEMP signals are ratiometric
to the V
RATIO
voltage; that is, the null voltage, rate sensitivity, and
temperature outputs are proportional to V
RATIO
. So the ADXRS612
is most easily used with a supply-ratiometric analog-to-digital
converter, which results in self-cancellation of errors due to minor
supply variations. There is some small error due to nonratiometric
behavior. Typical ratiometricity error for null, sensitivity, self-test,
and temperature output is outlined in Table 4.
Note that V
RATIO
must never be greater than AV
CC
.
Rev. 0 | Page 10 of 12
Table 4. Ratiometricity Error for Various Parameters
Parameter
V
S
= V
RATIO
= 4.75 V
ST1
Mean
0.4%
Sigma
0.6%
ST2
Mean
0.4%
Sigma
0.6%
Null
Mean
0.04%
Sigma
0.3%
Sensitivity
Mean
0.03%
Sigma
0.1%
V
TEMP
Mean
0.3%
Sigma
0.1%
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.
V
S
= V
RATIO
= 5.25 V
0.3%
0.6%
0.3%
0.6%
0.02%
0.2%
0.1%
0.1%
0.5%
0.1%
SELF-TEST FUNCTION
The ADXRS612 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 (±5%), 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 ADXRS612 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 a separate application note.