Magnetics Overview (03:23)
GMR Overview (02:00)
Today we're talking about magnetism with Daniela
at NVE. So, Danno, what causes magnetism?
In practical applications magnetic fields are either from permanent magnets or electric currents. Permanent magnetism is due to the intrinsic magnetic moments of electron spins.
Here's what the field from a disk magnet looks like:
[diagram showing flux lines from a disk magnet].
What happens to magnetic field strength over distance?
Close to the face, the magnet is like a monopole, so the field drops off with the square of the distance. Farther from the face, the field drops with the cube of the distance.
Here's an experimental setup for magnetic field strength vs. distance using a small ceramic magnet and an AAH002 magnetometer chip.
For this demonstration, we powered the magnetometer IC with a 9-volt battery, and connected it to a meter to measure the field versus distance.
As the magnet moves closer, the output increases.
[animation of magnetometer meter reading versus distance]
This graph summarizes the data:
[graph of sensor output versus distance]
The chart goes out to about an inch and a half. Can you detect a magnet farther away than that?
Maybe with a really big magnet. It depends on a number of things. In this example we start to get interference from the earth's magnetic field around here...
Most practical applications use spacings of a fraction of an inch, but sensitive sensors give you more signal to work with.
That's certainly "attractive." What's the actual field from the magnet?
Here's the same graph with the field in oersteds:
[graph of magnetic field strength versus distance]
For reference, the earth's magnetic field is about half an oersted.
[line for the earth's magnetic field]
Oersteds... Sometimes I hear tesla or gauss for magnetic fields. Whats the difference?
Tesla and gauss are units of magnetic flux density. One tesla is 10,000 gauss. Oersteds and amps per meter are different units of magnetic field strength. Oersteds and gauss have a one-to-one correspondence in air.
Thanks. Where can I get the parts you used in this video?
The sensor, magnet, and a circuit board for the sensor are in the AG-001 analog sensor evaluation kit, available from NVE or Digi-Key.
Today we're talking about spintronic "giant magnetoresistance" with Daniela
at NVE. Danno, why does a nanotech company make something "giant?"
refers to a giant change in resistance. GMR is actually a nanoscale phenomenon.
The balls represent electrons. The middle (conduction) layer needs to be thinner
than the mean free-path of conduction electrons, which is only a few nanometers.
The top layer is called the free layer because its electron spins are free to
change. The bottom is the pinned, or reference layer, because its spin orientation
is fixed when the device is made. In this state, the electrons spin in opposite
directions in the top and bottom layers, which causes the electrons in the middle
to scatter, increasing resistance. Then when a field is applied, spins in the
free layer switch, conduction electrons scatter less, and resistance drops. The
magic of GMR is turning the esoteric property of electron spin into resistance,
which can be used by conventional electronics. The large signals can mean smaller
size, more precision, and lower power. We can summarize these advantages with
the "three Bs": boxes, bits, and batteries.
are certainly "giant" advantages. What products use GMR?
come to mind:
* magnetic sensors
* gear-tooth sensors;
* GMR isolators.
And there are videos
on those applications and more on nve.com.
today we're "digging" into spintronic tunneling with Daniela at NVE.
So, Danno, what is tunneling and how does it work?
is a nano-scale phenomenon where under the right conditions, electrons can tunnel
through very thin, normally insulating materials, causing lower resistance. Structures
are called Magnetic Tunnel Junctions, or Tunneling Magnetoresistors. Let's look
at one. The section on the right is called the free layer, because its electron
spins are free to change, and the layer on the left is the pinned,
or reference layer, because its spin orientation is fixed when the device is made.
The barrier between the pinned and free layers is thin enough that electrons can
tunnel through, and as the meter shows, the resistance is low even though this
is a normally insulating material. When a field is applied, the free-layer polarization
switches, reducing tunneling, because of the scattering caused by electrons spinning
in opposite directions. So the tunnel-barrier returns closer to its insulating
state. In this way we can turn the esoteric property of electron spin into something
useful: resistance. The resistance change can be very large. Large signals can
mean smaller size, more precision, and lower power spintronic devices. Here's
an SEM of an actual tunnel junction made here at NVE. This white stripe is an
aluminum-oxide tunnel barriereight atoms thick. This is probably magnified nearly
a million times on your screen, so an eight-inch wafer would appear a hundred
miles in diameter.
Cool. How can our viewers "burrow"
You can go to nve.com for lots more info.
we're learning about "MRAM" with Daniela at NVE. So, Danno, what is
MRAM stands for Magnetoresistive Random
Access Memory. Unlike semiconductor memories that use electron charge to store
data, MRAM uses electron spin.
Why is that better?
charge, electron spin is inherently permanent. MRAM has been called the ideal
memory because of its potential to combine the speed of SRAM, the density of DRAM,
and the nonvolatility of flash memory.
So how does it
Let's look at what's called "classical" MRAM. Each bit
has a spin-dependent tunnel junction memory cell, and magnetic row and column
write lines. The spin-dependent tunnel junction produces a large change in resistance,
depending on the predominant electron spin in a storage layer. The tunnel barrier
is as thin as a few atomic layers. It's so thin, that depending on spin polarizations,
electrons can "tunnel" through the normally insulating material, causing
a resistance change.
Here's an SEM of an actual tunnel junction made here
at NVE. This white stripe is an aluminum-oxide tunnel barriereight atoms thick.
This is probably magnified nearly a million times on your screen, so an eight-inch
wafer would appear a hundred miles in diameter.
We have a separate video explaining "tunnel junctions."
in MRAM, data is read as the tunnel junction resistance. Data is stored in the
spin-polarization of a tunnel junction magnetic layer. The write lines create
magnetic fields that store data bits by setting magnetic spin polarization.
what's after "classical MRAM"?
MRAM could reduce cell size and power consumption. One next-generation technology
is Spin-Momentum Transfer, which changes the spin of storage electrons directly
with a spin-polarized electrical current, rather than an induced magnetic field.
This has the potential to significantly reduce MRAM write currents and self-heating.
Dannothat was "memorable." Go to nve.com for more info on
MRAM and spintronics.
Sensor Systems (02:00)
we're talking about GMR Switches with Jayne, at NVE. Jayne, what are "GMR
Switches" and how are they better?
GMR Switches are
precision digital magnetic field sensors with integrated GMR sensor elements and
on-board digital signal processing. As this slide shows, GMR Switches are more
accurate than other magnetic sensors, and magnetic operate points are stable over
voltage and temperature. This makes for precision, tight-tolerance magnetic sensing
And what parts are available?
GMR Switches can operate over a wide range of magnetic fields, making them the clear
choice for digital output magnetic sensors. NVE offers three series of GMR Switches:
AD-Series Digital Sensors with a 4.5 volt to 30 volt supply; ADV001-Series bipolar digital sensors; and AFL-Series digital sensors with supply
voltages as low as 0.9 volts. Parts are available in SOIC-8, MSOP-8, or 2.5 by
2.5 millimeter TDFN-6 packages.
Thanks, Jayne. Where
can I "switch" for more info?
You can click
to go to the digital sensor section of nve.com for info, or to get an evaluation
kit. Or call me, at 800-GMR-7141, extension 2.
Sensor Tips (02:33)
So what's with the bad hat and the music, dude? Is it some kind of geek chic?
Foolproof sensor circuits is today's topic.
Right. The unique NVE DB-002 power switch IC comes in a SOIC-8 and provides:
* short-circuit protection;
* reverse battery protection, and
* automatic thermal shutdown;
as well as signal processing, so sensor systems can be just about foolproof.
So where would you use that?
The IC is designed to work with NVE's AD-1 Series GMR magnetic switch, or any current sourcing, CMOS, or TTL output sensor element.
Some customers even use the IC to ruggedize inductive or photoelectric sensors.
What's a typical circuit?
Let's look at one. The DB-002 provides:
* a sourcing or sinking output with up to 300 milliamps. Integrated transient protection makes the circuit especially good for driving capacitive or inductive loads.
* The LED is driven with three milliamps when the output is on.
* Shutdown delay after a short-circuit is set by the one-nanofarad capacitor. A bigger capacitor makes for a longer delay.
* A 10 nanofarad minimum bypass cap is recommended between Vcc and ground.
* Vreg is a regulated, five-volt output, provided by the IC to power the sensor and other components in the assembly. For noisy environments, Vreg can be bypassed with up to a 100 nanofarad capacitor.
You would be a "fool" not to use that IC!
And you can buy them from the on-line store at nve.com.
vs. Omnipolar Magnetic Sensors (01:40)
today we're "gearing up" to talk about gear-tooth rotation sensors,
with Jayne at NVE. Jayne, tell us about GT Sensors.
GT Sensors are designed for detection of gear teeth and magnetic encoder wheels
in industrial speed sensing. As this slide shows, GT Sensors have four GMR sensing
resistors, which are connected as a Wheatstone bridge. The direction of sensitivity
is parallel to the sensor plane. A biasing magnet provides field, and the flux
lines are deflected into the direction of sensitivity by passing metal gear teeth.
The sensor produces a sinusoidal output with one cycle per tooth. GT sensors use
high-sensitivity, low-hysteresis GMR, to detect even the smallest gear teeth,
and to provide a 50 percent duty cycle output with wide air gap and temperature
How about some application tips for our viewers
to sink their "teeth" into?
Several things come
* About 1.5 millimeters between the back of the sensor
and the face of the bias magnet keeps flux-lines flexible and able to follow
* Locating the sensor and magnet on opposite sides of
a circuit board often provides good spacing.
* Use a thick
circuit board with a milled magnet pocket to precisely position the magnet on
a PCB. Most board manufacturers can do that.
* If you
don't need zero-speed operation, you can AC-couple the sensor to eliminate offset
* The right magnet is important. Ceramic-8
is cheap and has good field properties. Alnico-8 is good for high-temperature.
We don't recommend rare earth magnets because they can saturate the sensors.
Thanks, Jayne. Where can I "turn" for more info?
can click to go to the GT-Sensor section of nve.com for info, or to buy an
evaluation kit. Or call me at 800-GMR-7141, extension 2.
Angle Sensors (01:59)
Jayne, a question we get here in the NVE Applications Center is: what's the difference
between an "omnipolar sensor" and a "bipolar sensor," and
is that a question for a psychologist or an engineer?
question. Most NVE magnetic sensors are omnipolar, which means they're sensitive
to either polarity. But bipolar sensors are different, with opposite operate and
release points. Let's look first at an omnipolar sensor. Either a north or south
field turns the sensor On. The sensor turns off when the field is removed. An
opposite field also turns on the sensor. This is a bipolar sensor. A south field
above the sensor threshold latches the sensor On; and the sensor remains On after
the field is removed. A north magnetic field turns the bipolar sensor Off.
ADV001 is a great choice for bipolar applications.
would be handy in certain applications. Where can I get more info?
can click, to go to the digital sensor section of nve.com. Or call me, at
800-GMR-7141, extension 2.
Ultraminiature Sensors (01:20)
we're talking about "TMR" angle sensors with Jayne at NVE. Jayne, tell
us about these remarkable sensors.
AAT001 sensors use extremely high output spintronic Tunneling Magnetoresistors.
They sense angles around an axis perpendicular to their TDFN package. Typically,
they're used with a split-pole magnet to create flux-lines parallel to the package.
The sensor can determine angle and direction. As the magnet turns, the sensor
has two sinusoidal outputs ninety degrees out of phase. This quadrature lets you
determine direction of rotation. AATs can be used for angle sensing or precision
Why are AATs better than other angle
We summarize AAT advantages with three "Bs":
bits, meaning large, precise output signals, without amplification;
bounds, or wide air-gap tolerance, and;
* batterieshigh sensor
resistance means extremely low power consumption.
are popular applications?
Several come to mind:
* rotary encoders;
* automotive rotary position sensors;
* motor shaft position sensors; and
* knob position sensors.
Where can I "turn" for more info?
can click, to go to the AAT page in NVE's on-line catalog. Or call me, at 800-GMR-7141,
for Sensor Systems (03:08)
thinking small today, as we learn about ultraminiature ULLGA sensors, with Jayne
at NVE. Jayne, what's a "ULLGA?"
for Ultra Leadframe Land Grid Array. The ULLGA package is a unique, 1.1 millimeter-square,
surface-mount sensor. These are NVEs smallest packaged sensors. This coffee
cup holds 700,000...
Hey! Don't drink that, Dude!
let's take a closer look: 1.1 millimeters square with four 400-micron pads. The
parts are smaller than the head of a pin. In addition to their small size, ULLGA
parts are available in nanopower versions. And all NVE digital sensors have extremely
stable operate points over voltage and temperature.
how can our viewers reach you for a "little" more info?
me at email@example.com, or call me at 800-GMR-7141, extension
IsoLoop Isolators Work (02:18)
today we're "sticking" to magnets with Jayne at NVE. Jayne, tell us
which magnets are "attractive" in sensor systems.
The right magnet can make a big difference in system performance, often
not much cost. Let's start by looking at magnet configurations.
Magnets are often used
with simple proximity sensors, such as this GMR Switch. The magnet might also
bias a sensor like this GT gear-tooth sensor, so the field is deflected by passing
What are some differences in magnets?
main things: material grades, material, and shape.
First, material grades: Ceramic and Alnico magnetic materials are graded between one and eight. Grade one
materials are non-oriented or isotropic. In general, higher grades are more fully
oriented and have higher field strengths. Cost goes up with material grade.
Turning to materials:
* Ceramic, or ferrite, magnets are made of strontium
carbonate and iron oxide.
* Grade-one have the weakest magnetic field strengths, grade five
are inexpensive and popular, while grade eight have good field characteristics
for sensor systems but are still fairly inexpensive.
* Alnico refers to aluminum-nickel-cobalt alloys. Alnico magnets have working temperatures above
500 degrees Celsius. Alnico grade eight magnets provide a very stable field
over wide temperature ranges, making them the preferred choice for high temperature
* Rare-earth magnets, such as samarium-cobalt or neodymium-iron-boron,
are expensive and have very high field strengths. The high field strengths are
generally not necessary with NVE sensors, and may actually saturate the sensors.
There are almost infinite magnet sizes and shapes. Some of the more common
with our customers are bar magnets around one-half inch long, and disks an eighth
to a quarter-inch in diameter. A couple of specialty-type magnets are
used in sensor systems:
* Split-pole disk magnets are used for angle sensors
such as AAT001s. Split-pole magnets have poles on opposite sides of the diameter,
rather than top and bottom.
* And ring magnets have a number of poles
around the diameter for rotational or course-angle sensing. Ring magnets are
common in ABS brake systems, for example, and can be used with GT Sensors.
So "rare" on earth can our viewers get some of the magnets you talked about?
You can click, to go to the magnet section of our on-line store.
Isolator Overview (03:44)
here with Sandy, in the NVE Applications Center. Sandy, can you explain how NVE's
award-winning "IsoLoop" isolators work?
But first, let's look at optocouplers. As this shows, optocouplers
transmit signals by light through a dielectric that provides galvanic isolation.
The optical elements are slow, have limited life, and limit size.
Doesn't everyone. But IsoLoop couplers use
spintronics and magnetics, rather than optics, to transmit data. They consist
of spintronic GMR resistors, microscopic integrated coils, and conditioning electronics.
The GMR resistors are spin valves with two stable resistance states. A dielectric
provides isolation. The coil creates a magnetic field proportional to the input
current. The field changes the spin polarization of the spin valves, which changes
their resistance. The output is amplified and conditioned to produce an isolated
replica of the input.
So, IsoLoops transmit signals by
magnetic field and electron spin, rather than light and photons?
And because ground potential variations are common to both sides of the coil,
they don't generate a current. This yields a large common-mode rejection ratio
and true galvanic isolation.
Cool. And you said they were
smaller and faster?
Darn right. IsoLoops are available
in MSOPs, narrow and wide SOICs, plus PDIPs, with up to five channels per device.
They run up to 150 megabits per second, and up to 125 degrees C.
Way cool. Where can I get data sheets or more info?
You can click, to go to the isolator section of nve.com. Or call us, at 800-GMR-7141,
Isolator Speed Metrics Explained (04:13)
I'm here with Sandy, in the NVE applications center. Sandy, tell us about NVE's industry-leading
IsoLoop "IL700" isolators.
Sure. Here's a single-channel
functional diagram. IL700 isolators are digital-in, digital-out galvanic isolators.
They use spintronic GMR rather than optical technology. Key features include 5-
or 3-volt operation; 2,500-volt isolation, which complies with UL1577 and IEC61010.
Parts also feature low EMC footprint and best-in-class speed and distortion, with
many I/O configurations, packages, and variants.
What I/O configurations are there?
Just about all possible
one, two, four, and five channel configurations are available. There are also
several variants for particularly demanding applications:
* IL200 series have five channels per package.
* Dash-one series, are
MSOP-8s, the world's smallest isolators.
* "S" stands
for speed, at 150 megabits per second and lowest pulse-width distortion, of 300 picoseconds.
* Finally, T-Series IsoLoops have the highest operating
temperature of 125C.
What parameters set IL700s apart?
Here are a few:
* highest data rate;
* lowest distortion as measured by PWD, prop delay, skew, and jitter;
* excellent transient immunity; and
* wide temperature ranges.
We summarize the advantages with the four "Bs":
* Boxespackages to maximize channel density or creepage;
* Bitsup to five channels per device;
* Baudhighest speed and lowest distortion; and
* Bulletproof, including temperature, transients, and barrier
The four "Bs." As you British say, "brilliant."
What packages are available?
Several choices. I mentioned
MSOPs for highest channel density. There are:
* eight-pin SOICs and PDIPs for drop-in replacement;
* 16-pin narrow SOICs, for four, or five channels per package, plus
* wide SOICs or PDIPs for maximum creepage and clearance.
What are popular applications?
A lot of IL700s replace optocouplers for higher speed, less distortion, longer life,
and higher channel density.
I hate optos...
the club. And other popular IL700 applications include:
* serial interfaces;
* isolated SPI;
* isolated A-to-D converters; and
* power interfaces.
Where can our viewers get data sheets and samples?
You can click, to go to the IL700 section of our on-line store for samples and data sheets.
Megabaud vs. Megahertz (01:24)
We're talking about isolator speed with Sandy, at NVE. Sandy: PWD, skew, jitter. All the terms give me the "jitters."
Let's cover key isolator speed metrics. Starting with data rate, which is the maximum rate at which data can be transmitted. Simple enough, but some companies specify a data rate faster than the propagation delay. This is a waveform for an actual device. The data is more than five cycles behind. By the time the data shows up on the output, not only are we on the next clock cycle, it's several cycles behind. And other parameters can make claimed data rate unusable. For example, one competitor's datasheet requires zero rise and fall time and exactly 50% duty cycle. Obviously unrealistic.
That's so lame. NVE would never do that...
That's why "Usable Data Rate" is important. UDR is defined as the maximum rate before the data is a cycle behind. So with this propagation delay the full data rate is usable.
Gotcha. And how's "Propagation Delay" defined?
Righty-O. "Propagation Delay" is the time for an edge to propagate. The faster the device the shorter the prop delay. There are also some important metrics related to prop delay. Because fast is worthless if it's garbled:
"Pulse-Width Distortion" is the maximum difference in rising and falling prop delays. As you can see here, the asymmetry distorts the pulse width--in this case, making it wider. This is important in pulse width modulation and delta-sigma ADCs.
"Channel-to-Channel Skew" is the difference in propagation delay between channels in the same device. It can be either direction. It's important for clocked systems.
"Propagation Delay Skew" is the difference in propagation delay between devices. Also important for clocked systems. It's larger than "Channel-to-Channel Skew," and can be a trap for the unwary in synchronous systems. This is an area where IsoLoop isolators shine.
"Jitter" is another under-reported parameter. It's the variation in the pulse edge position and can cause particularly nasty distortion.
So what are some specs for those?
Here are the specs for NVE's high-speed IL700-S Series parts:
* "Data Rate";
* and "Usable Data Rate" are the same for NVE devices;
* "Propagation Delay" is the time for an edge to propagate;
* "Pulse-Width Distortion" is the change in pulse width at the output;
* "Propagation Delay Skew" is the difference in propagation delay between devices;
* "Channel-to-Channel Skew" is the difference in propagation delay between channels in the same device; and
* "Jitter" is the variation in the pulse edge position.
The NVE parts are best in class for speed parameters.
Thanks, Sandy. Where do you "propagate" more "unskewed," "usable" info?
You can go to nve.com, or call us at 800-GMR-7141, extension four.
a question we got here in the NVE Applications Center: the IL700 data sheet specifies
a maximum data rate of at least 100 megabits per second, but the maximum frequency
is 50 megahertz. So what's the difference between "baud" and "hertz"?
question. As you can see, there are two bits of data in every 50 nanosecond cycle
running at the maximum speed. Therefore, the max data rate is twice the max frequency.
So the maximum data rate is 100 megabits per second for 50 megahertz devices like
IL700-Series Isolators. Extracting, or qualifying, that data requires a 100 meg
clock, but the maximum transfer rate is still 100 megabits per second. In addition
to best-in-class speed, IsoLoop Isolators have remarkable pulse-width distortion
and jitter specifications. Because fast is worthless if its garbled.
Sandy. Where can I get data sheets or more info?
You can click to go to the isolator section of nve.com. Or call us, at 800-GMR-7141,
Layout Tips (02:02)
Today we're talking about RS-485 design with Sandy in the NVE Applications Center. Sandy,
give us the "four-one-one" on "four-eight-five" to avoid a bus "nine-one-one."
Sure. RS-485 is a bidirectional, half-duplex transmission system, so data
can be transmitted in both directions, but only one direction at a time.
RS-485 allows up to 32 unit-loads, although fractional-load transceivers
like the NVE IL3285 allow up to 256. Transceivers connect the nodes. Pull-up
and pull-down resistors can make the network fail-safe. Several bus configurations
are possible. These configurations have long stubs that can cause reflections.
"C" and "D" are ideal because the nodes are in a continuous
line, although not necessarily straight. Short spurs to intermediate nodes
are often necessary. If so, stub lengths should be less than one-sixth of
the electrical signal length. This is the formula for electrical signal
length: using typical values of 10 nanoseconds rise time and 78 percent
propagation velocity, we get an electrical signal length of 2.3 meters.
So the maximum stub length is one-sixth of the electrical length, or 39 centimeters.
And how long can we have the main bus?
Well, the longer the
cable, the slower the data rate. RS-485 can transmit over 1,200 meters, or 10 megabits per second, but not both. This graph shows the typical tradeoff, depending on noise and jitter tolerance.
What about terminating lines?
point. Unterminated lines are only suitable for very low data rates, and very
short cables, otherwise reflections cause errors. Both ends of the bus, but not
every node, should be terminated. Finally, for a fail-safe configuration, bias
for at least 200 millivolts with no active drivers. This ensures the bus will
be in a known state.
Don't forget about isolation!
reduces noise, eliminates ground loops, and improves safety. IsoLoop Isolators
are faster, more reliable, and simpler than Optocouplers. Here's an opto isolation
board full of components.
That's a lot of parts...
But IsoLoop isolators provide a single-chip solution, combining isolation with
communication functions. There's a full line of isolated transceivers, including
the workhorse IL485, the high-speed IL3585, the fractional-load IL3285, and the
low-cost IL3185. There are 16-pin wide-body SOICs and ultra-miniature narrow-body
parts. So let's sum up with my RS-485 tips:
* keep stubs short;
* use twisted-pair cable;
* shielding for long or fast busses;
* ground one end of the shield;
* terminate bus ends;
* bias for fail-safe; and, of course,
* use isolators.
Thanks Sandy. Where can viewers go for more info?
You can click, to go to the RS-485 Application
Center at nve.com. Or call us at 800-GMR-7141, extension four.
we're going to learn best practices for data converter board layout with Sandy
in the NVE Applications Center. So how do we optimize data conversion?
are two under-appreciated keys to data converter performance. First, PCB layout;
and second, isolation. Here's an example of a not-so-good layout. The customer
expected about 92 decibels signal-to-noise plus distortion. But he got closer
to just 80.
Eighty decibels! Where did he go wrong? He has a ground plane...
Yes, but high-speed digital currents
are still injected into analog paths. So here we've moved the ADC closer to the
supply, and made sure digital grounds don't travel across, under, or parallel
to analog signals. But there's still noise from digital ground currents. And that
can be eliminated with isolation.
Here's the equivalent circuit for the
non-isolated board. Asynchronous noise is injected into the ADC ground. But isolation
separates the digital and analog paths. Current spikes are routed to ground without
interfering with the analog signal. Complete galvanic isolation and best performance
is achieved by using separate analog and digital power supplies, which is possible
Where can I learn more about getting on "board?"
You can click to go to the data converter
application center at nve.com. Or call us at 800-GMR-7141, extension four.
What's with the set and music?
We're talking about "spy."
No, this spy is "S-P-I," which stands for Serial Peripheral Interface, which
is a common bus for ADCs and DACs. Isolating SPI eliminates ground loops and reduces
noise, which improves accuracy. Here's a single-channel isolated SPI Delta-Sigma
A-to-D Converter using an IL717. The ADC is located on the bridge with no signal
conditioning electronics between the bridge sensor and the ADC. The IL717 isolates
the SPI control bus from the microcontroller, and the system clock is on the isolated
side of the system.
What if I have multichannel A-to-Ds?
Then you need an IL200-Series five-channel isolator. For example, the IL262 dash-3 has
five channels in a 0.15-inch SOIC-16. This circuit is an example of a multi-channel
sampling system with separate A-to-D cells. The IL262 is used to control the SPI
lines and send ADC-busy commands back to the host, for efficient interrupt-driven
sampling. The busy line can also be used as a frame synchronization signal in
I love video. But I hate optos. How are IsoLoops better?
IsoLoops are ideal for
SPI because they have higher speed, less distortion, unlimited life, and higher
channel density than optos.
Where can a guy "spy" more on SPI?
You can click to go to the SPI application
center at nve.com. Or call us at 800-GMR-7141, extension four.
Audio Isolation (01:26)
with the music?
The Can-Can, because we're talking about
CAN-bus in the NVE Applications Center.
Well, CAN bus
isolation is a good idea and allows higher speed and more reliable operation by
eliminating ground loops and reducing susceptibility to noise and E-M-I. And,
in high-voltage Battery Management Systems, isolation improves safety. To complement
stand-alone CAN transceivers, NVE has several two-channel, bidirectional isolators,
including unique MSOPs. The new IL721 bidirectional isolator is similar to the
popular IL712, but with a reversed channel configuration to better suit some layouts.
Both the IL721 and IL712 have best-in-class ten nanosecond propagation delay.
This minimizes loop delay and maximizes speed over a given bus length.
How about single-chip isolated transceivers?
Right. IL41050 single-chip isolated transceivers simplify CAN circuits even more. They fully
comply with ISO 11898 and de facto industry standards. Loop delay is a
best-in-class 180 nanoseconds. And advanced features make for reliable bus operation.
Wide-body and narrow-body versions are available.
saying you "can" isolate "CAN." So then where "can"
I get data sheets and more info?
You can click, to go to the isolator section of nve.com. Or call us at 800-GMR-seventy one
four one, extension four.
Passive-Input Isolators (01:30)
talking jitter with Sandy in the NVE Isolator Applications Center. Sandy, what
is isolator "jitter" and why is it important?
can be a problem with conventional isolators. As this shows, jitter is variation
in the pulse edge position of a data stream.
just so sad!
Indeed. But NVE's IL700 isolators have a
virtually undetectable 50 picoseconds of jitter, making them ideal for precision
How do isolators help audio circuits?
ways. First, galvanic isolation can eliminate hum and noise. And second, low jitter
ensures PCM data phase.
Can you give an example?
Here's a typical circuit. It's good practice to isolate serial CD, or MP3
data from the analog sound system. This eliminates ground loops, speaker hum,
and high frequency pickup caused by digital currents in analog paths.
that "sounds" good. Where can I get more info?
You can click to go to the iso application centers at nve.com. Or call us at 800-GMR-7141,
True 8 (true 8 mm creepage) Isolator
we're talking about, NVE's award-winning passive-input, drop-in opto-isolator
replacements. Sandy, what's "passive input"?
CMOS input isolators, IL600s have a current-sensitive, resistive coil, like an
LED input, but without the voltage drop. The outputs also mirror LED optos with
CMOS and open-drain options. A variety of one, two, and three channel models are
available to upgrade from optos.
Well, I hate optos. Why
are IL600s better?
We summarize the advantages with, four
* Boxesdrop-in PDIPs or SOICs, plus unique ultra-miniature
* Boundsflexible inputs, CMOS or open-drain options;
Baudhigher speed and less pulse-width distortion; and
Bulletproof, with no LED to be damaged and no degradation with time.
"four Bs." As you British say, "brilliant." Where can viewers
get datasheets and samples?
You can click, to go to the
IL600 section of our on-line store for samples and datasheets.
High-Voltage Standards (02:36)
We're learning about NVE's exclusive, True 8 millimeter, creepage Isolators,with Tammy, in the NVE Application center. Tammy, give us the "truth" about isolator packages.
Creepage is the minimum spacing over insulation. Stringent rules are set by IEC60601. Sixteen-pin wide-body SOICs are popular for isolators, but most don't meet the 8 millimeter creepage requirement.
Why so, Tamarino?
With most packages, JEDEC tolerances, mold variability, and surface metal in the creepage path mean full 8 millimeter creepage can't be assured.
The shortest creepage path is usually around the end of the package. Ordinary JEDEC wide-body packages are nominally 7.4 millimeters wide, with approximately
8.1 millimeters between pins around the end, before subtracting tie bars.
I used to wear tie bars...
Well, these tie bars are tabs used in the molding process. Internally connected or not, the exposed metal reduces creepage. The tie bar subtraction, for an ordinary JEDEC package is typically half a millimeter, bringing creepage to 7.4 to 7.6 millimeters. That's not enough for 250 working volt applications, even before tolerances.
So how are NVE True-8 packages, different?
Instead of a general-purpose package, we custom tooled the True 8 package. It's within the JEDEC standard, so there's no special board layout or handling.
It has much tighter tolerances on package width, and pin position. And, rather than two metal tabs, the True 8
has just one thin tab that secures the lead-frame during molding. Creepage around the end is calculated as the package edge width, plus two pin-to-end
spacings, less the surface metal. Even with worst-case package dimensions and pin placement, the True 8 ensures 8.03 millimeters minimum
creepage. The path over the top is also specified for 8 millimeters. Eliminating the outdated pin-1 edge chamfer, ensures over-the-top creepage.
So, what parts come in the True 8 package?
There are oodles of True 8 parts: high-performance IL700/200 Series Isolators, single-chip transceivers, cost-effective IL500s, and IL600 Passive Input Isolators. Common applications include serial busses, SPI, A-D converters, and power interfaces.
Thanks, Tammy. How can viewers learn more about the True 8 package?
We have links to application bulletins, or call us at 800-GMR-7141,
learning about how isolators improve electrical safety with Sandy, in the NVE
Applications Center. Sandy, give us the "four-one-one" on how to avoid
a "nine-one-one" under 61010 or 1577.
explain that UL1577 is the safety standard for optical isolators and IEC61010-2001
provides safety requirements for electrical equipment for measurement, control,
and laboratories. IsoLoop Isolators are approved under both standards. There are
details in IsoLoop datasheets.
What high-voltage info is
in the datasheets?
Let's summarize. NVE offers five package
types. MSOPs, SOIC-8s, PDIPs, and narrow and wide SOIC-16s. Creepage distance
is the shortest path between conductors along the surface. That's over the top
for IsoLoops. Working voltage is the highest voltage the isolator sees in normal
operation. This is typically the line voltage, so 120 or 150-volt parts are usable
in 120-volt equipment, and 300-volt parts are used for 240. IsoLoop isolators
are 100 percent tested at high voltage to ensure they will work in the field.
volts would sure put a jolt in your "knickers." Why so high for a 300-volt
Test voltages are much higher than working voltage
to take into account possible large transient over-voltages. Like optocouplers,
these ratings are for:
* installation category 2, which specifies
the transient over-voltages;
* pollution degree 2 specifies
cleanliness of the operating environment; and
* material group 3 relates to carbon tracking susceptibility.
And most importantly, IsoLoop
Isolators are proven in demanding, real-world applications.
Sandy. How can viewers learn more about high-voltage performance?
You can click, for links to relevant application bulletins. Or call us at 800-GMR-7141,
Barrier Life (02:05)
Here's a question we get in the NVE Applications Center. Isolation voltage for
most NVE isolators is 2,500 volts for a minute. But what voltage can they stand
The maximum voltage indefinitely between
the inputs and outputs of an isolator is called endurance voltage. It's typically
not in data sheets, and may be the least familiar high-voltage specification.
But it's useful in applications where the isolators aren't subject to line voltage
transients. IsoLoop RMS endurance voltage is 800 volts.
where's "endurance voltage" important?
management systems come to mind. Here the last isolation stage is 300 volts above
controller ground. So the isolator sees 300 volts between inputs and outputs.
With an endurance voltage of 800 volts RMS or 1,130 volts peak, the isolators
can be expected to withstand up to 1,130 volts DC indefinitely, and will easily
withstand the voltages in this circuit.
Where can I get more info?
You can click to go to the ISO Application Centers at nve.com. Or call us at 800-GMR-7141, extension
I'm here with NVE's Quality Guru. Dee, do IsoLoop isolators really last "forever"?
For practical purposes, forever. Optos use LEDs, which degrade over time. Every photon emitted depletes the LED, so the output decreases and eventually it will fail.
That's one reason engineers hate optos.
Sure. But IsoLoop isolators use magnetics and spintronics rather than optics. Nothing is depleted. Nothing degrades with time. Think of a microwave versus an Easy Bake oven.
What about the life of the isolation barrier?
The isolation barrier is a patented glass-polymer structure that doesn't degrade. Compared to conventional semiconductors, its like indestructible fiberglass versus rusting sheet metal.
Do you have data to back that up?
Absolutely. Our reliability data show failures-in-time of 2.6 per billion hours at 100 degrees C, for an MTBF of 44,000 years. Some conventional semiconductor isolators brag about a barrier life of just 13 years.
Thirteen years gives engineers "FITs." Heck, even my ties last longer than that. So you've had parts on life test since the Pleistocene era?
Well, at least since the Reagan administration, with standard Fits extrapolations.
How can viewers get IsoLoop reliability reports?
You can contact us at ISOfirstname.lastname@example.org.