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ADI | Engineering a More Sustainable Future
Magnetic Encoder (AMR)
Sensing
In the field of magnetic-based position sensors, AMR sensors
provide the best combination of robustness and accuracy. The
sensor is typically positioned opposite a dipole magnet attached to
the motor shaft as depicted in Figure 6.
AMR sensors are sensitive to magnetic field direction changes,
unlike Hall technology that is sensitive to field intensity. The
resulting advantage is that the sensor is very tolerant to airgap and
mechanical tolerance variation in the system. Also, as there is no
operating magnetic field upper limit with AMR sensors, the sensor
is extremely robust to stray magnetic fields when operating with a
high magnetic field.
The ADA4571 is an AMR sensor with low latency integrated
signal conditioning and provides a single-ended analog output.
The ADA4571 single-chip solution provides guaranteed angular
accuracy (only 0.10 typical angular error) and can operate at
speeds up to 50k rpm. The ADA4571-2 is a dual version that
provides full redundancy without compromising performance in
applications that are safety critical.
The ADA4570 is a derivative of the AAD4571 with the same
performance but with a differential output for use in harsher
environments. The high angular accuracy and repeatability
provided by the ADA457x family improve closed-loop control,
reducing motor torque ripple and noise. The single-chip
architecture improves reliability, reduces size and weight, and is
easier to integrate compared to competing technologies.
Signal Conditioning and Power
The AD7380 4 MSPS dual simultaneous sampling, 16-bit SAR ADC
provides many system-level benefits, including a space-saving 3
mm × 3 mm package important for space-constrained encoder
PCB boards. The 4 MSPS throughput rate ensures that detailed
sine and cosine cycles are captured, and encoder positions are up
to date. The high throughput rate enables oversampling on-chip,
which reduces the time penalty of digital ASICs or microcontrollers
feeding the precise encoder position to the motor. An extra benefit
of the AD7380's on-chip oversampling is that it allows for an
additional 2 bits of resolution, which can be easily used with an on-
chip resolution boost feature. Application note AN-2003
3
details
this oversampling and resolution boost feature of the AD7380. The
VCC and VDRIVE of the ADC and the supply rails of the amplifier
driver can be powered by an LDO regulator, such as the LT3023.
Multiple output low noise LDOs such as the ADP320, LT3023, and
LT3029 can be used to power all components in the signal chain.
Transceiver
The ADM3066E RS-485 transceiver features ultralow transmitter
and receiver skew performance, which makes these devices ideal
for transmission of a precision clock, which is often featured in
motor encoding standards, such as EnDat 2.2.
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The ADM3065E
has been demonstrated to show less than 5% deterministic
jitter across typical cable lengths encountered in motor control
applications. The wide supply range of the ADM3065E means
this level of timing performance is available for applications that
require either a 3.3 V or 5 V transceiver power supply. For more
information, see the technical article "Going Faster and Further
with Fieldbus."
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Microcontroller
For applications that require lower resolutions of 12 bits or less,
an alternative to using an AD7380 ADC is a microcontroller with
integrated ADC. The tiny MAX32672 ultra low power Arm® Cortex®-
M4F microcontroller includes a 12-bit 1 MSPS ADC with enhanced
security, peripherals, and power management interfaces.
Asset Health Monitoring
The ADXL371 is an ultralow power, 3-axis, digital output, ±200
g microelectromechanical system (MEMS) accelerometer for
machine monitoring. The ADXL371 is cost-effective, available in
a small 3 mm × 3 mm package, and operates at up to +105°C. In
instant on mode, the ADXL371 consumes 1.7 μA while continuously
monitoring the environment for impacts. When an impact event
that exceeds the internally set threshold is detected, the device
switches to normal operating mode fast enough to record the
event.
The ADT7320 is a high accuracy digital temperature sensor, which
requires no user calibration or correction and excellent long-term
stability and reliability. The ADT7320 is rated for operation over an
extended range of −40°C to +150°C and is available in a small 4 mm
× 4 mm LFCSP package.
