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ADXRS150_15 Datasheet(Arkusz danych) 10 Page - Analog Devices

Numer części ADXRS150_15
Szczegółowy opis  150/s Single Chip Yaw Rate Gyro with Signal Conditioning
Pobierz  12 Pages
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Producent  AD [Analog Devices]
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Rev. B | Page 10 of 12
The –3 dB frequency is set by RSEN (the parallel combination
of RSEN1 and RSEN2) at about 4.5 kΩ nominal; CMID is less well
controlled since RSEN1 and RSEN2 have been used to trim the rate
sensitivity during manufacturing and have a ±35% tolerance. Its
primary purpose is to limit the high frequency
demodulation artifacts from saturating the final amplifier stage.
Thus, this pole of nominally 400 Hz @ 0.1 µF need not be
precise. Lower frequency is preferable, but its variability usually
requires it to be about 10 times greater (in order to preserve
phase integrity) than the well-controlled output pole. In general,
both –3 dB filter frequencies should be set as low as possible to
reduce the amplitude of these high frequency artifacts as well as
to reduce the overall system noise.
The full-scale measurement range of the ADXRS150 can be
increased by placing an external resistor between the
RATEOUT (1B, 2A) and SUMJ (1C, 2C) pins, which would
parallel the internal ROUT resistor that is factory-trimmed to
180 kΩ. For example, a 330 kΩ external resistor will give
approximately 8.1 mV/°/sec sensitivity and a commensurate
~50% increase in the full-scale range. This is effective for up to a
4× increase in the full-scale range (minimum value of the paral-
lel resistor allowed is 45 kΩ). Beyond this amount of external
sensitivity reduction, the internal circuitry headroom require-
ments prevent further increase in the linear full-scale output
range. The drawbacks of modifying the full-scale range are the
additional output null drift (as much as 2°/sec over tempera-
ture) and the readjustment of the initial null bias (see the Null
Adjustment section).
It is common practice to temperature-calibrate gyros to
improve their overall accuracy. The ADXRS150 has a tempera-
ture-proportional voltage output that provides input to such a
calibration method. The voltage at TEMP (3F, 3G) is nominally
2.5 V at 27°C and has a PTAT (proportional to absolute tem-
perature) characteristic of 8.4 mV/°C. Note that the TEMP
output circuitry is limited to 50 µA source current.
Using a 3-point calibration technique, it is possible to calibrate
the ADXRS150’s null and sensitivity drift to an overall accuracy
of nearly 300°/hour. An overall accuracy of 70°/hour or better
is possible using more points. Limiting the bandwidth of the
device reduces the flat-band noise during the calibration process,
improving the measurement accuracy at each calibration point.
The ADXRS150’s RATEOUT signal is nonratiometric, i.e., nei-
ther the null voltage nor the rate sensitivity is proportional to
the supply. Instead they are nominally constant for dc supply
changes within the 4.75 V to 5.25 V operating range. If the
ADXRS150 is used with a supply-ratiometric ADC, the
ADXRS150’s 2.5 V output can be converted and used to make
corrections in software for the supply variations.
Null adjustment is possible by injecting a suitable current to
SUMJ (1C, 2C). Adding a suitable resistor to either ground or
the positive supply is a simple way of achieving this. The nomi-
nal 2.5 V null is for a symmetrical swing range at RATEOUT
(1B, 2A). However, a nonsymmetric output swing may be suit-
able in some applications. Note that if a resistor is connected to
the positive supply, supply disturbances may reflect some null
instability. Digital supply noise should be avoided particularly in
this case (see the Supply and Common Considerations section).
The resistor value to use is approximately
VNULL0 is the unadjusted zero-rate output, and VNULL1 is the target
null value. If the initial value is below the desired value, the
resistor should terminate on common or ground. If it is above
the desired value, the resistor should terminate on the 5 V sup-
ply. Values typically are in the 1 MΩ to 5 MΩ range.
If an external resistor is used across RATEOUT and SUMJ, the
parallel equivalent value is substituted into the above equation.
Note that the resistor value is an estimate since it assumes VCC =
5.0 V and VSUMJ = 2.5 V.
The ADXRS150 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 inputs ST1 (5F, 5G), ST2 (4F, 4G), or
both. ST1 causes the voltage at RATEOUT to change about
–0.66 V, and ST2 causes an opposite change of +0.66 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.
Since ST1 and ST2 are not necessarily closely matched, actuat-
ing both simultaneously may result in an apparent null bias
The one-chip integration of the ADXRS150 gives it higher reli-
ability than is obtainable with any other high volume manufac-
turing 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. How-
ever, some applications may warrant continuous self-test while
sensing rate. Application notes outlining continuous self-test
techniques are also available on the Analog Devices website.

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