ADXRS649 Data Sheet
Rev. B | Page 10 of 12
TEMPERATURE OUTPUT AND CALIBRATION
It is common practice to temperature-calibrate gyros to improve
their overall accuracy. The ADXRS649 has a temperature propor-
tional voltage output that provides input to such a calibration
method. The temperature sensor structure is shown in Figure 19.
The temperature output is characteristically nonlinear, and any
load resistance connected to the TEMP output results in decreasing
the TEMP output and its temperature coefficient. Therefore,
buffering the output is recommended.
The voltage at TEMP (F3, G3) is nominally 2.5 V at 25°C, and
V
RATIO
= 5 V. The temperature coefficient is ~9 mV/°C at 25°C.
Although the TEMP output is highly repeatable, it has only
modest absolute accuracy.
V
RATIO
TEMP
R
FIXED
R
TEMP
09573-019
Figure 19. Temperature Sensor Structure
MODIFYING THE MEASUREMENT RANGE
The ADXRS649 scale factor can be reduced to extend the
measurement range to as much as ±50,000°/sec by adding a
single 120 kΩ resistor between the RATEOUT and SUMJ pins.
If an external resistor is added between RATEOUT and SUMJ,
C
OUT
must be proportionally increased to maintain correct
bandwidth.
NULL BIAS ADJUSTMENT
The nominal 2.5 V null bias is for a symmetrical swing range at
RATEOUT (B1, A2). However, a nonsymmetric output swing
may be suitable in some applications. Null bias adjustment is
possible by injecting a suitable current to SUMJ (C1, C2). Note
that supply disturbances may reflect some null bias instability.
Digital supply noise should be avoided, particularly in this case.
SELF-TEST FUNCTION
The ADXRS649 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. The self-test is activated
by standard logic high levels applied to Input ST1 (F5, G5),
Input ST2 (F4, G4), or both. ST1 causes the voltage at RATEOUT
to change by approximately −0.15 V, and ST2 causes an opposite
change of +0.15 V. The self-test response follows the viscosity
temperature dependence of the package atmosphere,
approximately 0.25%/°C.
Activating ST1 and ST2 simultaneously does not damage the
part. 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 ADXRS649 gives it higher reliability
than is obtainable with any other high volume manufacturing
method. In addition, it is manufactured under a mature BiMOS
process that has field-proven reliability. As an additional failure
detection measure, a power-on self-test can be performed. How-
ever, some applications may warrant continuous self-test while
sensing rate. Information about continuous self-test techniques
is also available in the AN-768 Application Note, Using the
ADXRS150/ADXRS300 in Continuous Self-Test Mode.
