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ADI | Engineering a More Sustainable Future
Powering a 10BASE-T1L Sensor Prototype
Figure 5 shows a power supply design for a digital wired MEMS
sensor. The LT8618 is specifically designed for industrial sensors
with:
X Wide input range up to 60 V
X Low output current 100 mA
X Up to 90% efficiency
X Tiny 2 mm × 2 mm LQFN packages
Figure 5 shows the LT8618 with a 24 V
DC
input, which is regulated
to 3.7 V, and then input to the LT3042, which supplies 3.3 V to the
MEMS sensor circuitry.
The LT3042 is a high performance ultralow noise LDO regulator
with:
X Ultralow rms noise at 0.8 µV rms (10 Hz to 100 kHz)
X Ultrahigh PSRR (79 dB at 1 MHz)
X Tiny 3 mm × 3 mm DFN packages
The article "How to Get the Best Results Using LTspice for EMC
Simulation—Part 1"
2
details an LTspice simulation circuit and
discusses the EMC performance for the LT8618 and LT3042.
Figures 19 and 20 from the article show simulation results for
where an EMC disturbance is applied at the LT3042 input. This
shows that the LT3042 has less than 200 µV of voltage ripple even
in the presence of a 1 V p-p EMC disturbance at its input.
Integrating a Digital Hardware Design and
a Mechanical Enclosure
A steel or aluminum enclosure is used to house a MEMS vibration
sensor and provide solid attachment to monitored assets, as well
as providing water and dust proof-ness
(
IP67
)
. For vibration sensors,
the natural frequencies of the enclosure must be greater than that
of the applied vibration load measured by the MEMS sensor.
The frequency response plot for the ADXL1002 MEMS is shown in
Figure 6. The ADXL1002 3 dB bandwidth is 11 kHz and it has a 21
kHz resonant frequency. A protective enclosure used to house
the ADXL1002 needs to have a first natural frequency of 21 kHz or
greater in the axis of sensitivity. Similarly, when designing a triaxial
sensor, the natural frequencies of the mechanical enclosure need
to be analyzed across vertical and radial directions.
Sensor prototypes are tested on modal shakers, which provide
a controlled environment to set vibration test levels and sweep
across frequency. The test results of sensor frequency response
should closely follow the MEMS sensor information shown in Figure 6.
Modal Analysis
Modal analysis is a commonly used technique to provide a good
understanding of the vibration characteristics of enclosures.
Modal analysis provides the natural frequencies and normal modes
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