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Eric.Siegel

Mar 18, 2015

ISO7340C

digital isolators

ISO7342C

analog
blog

reinforced
digital galvanic isolators

ISO7341C

Basic
galvanic isolation

reinforced
isolation

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Don’t procrastinate, isolate! The need for a basic galvanic
isolator

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Digital
galvanic isolation has an important part to play in the world. It does an
amazing thing: it protects precarious products from unscheduled electrical
blowback like a suit of armor might against an unsuspected ricochet on the
battlefield.

In addition to this protection, it also facilitates communication between
devices.  Sometimes two devices might be on different ground planes but
still need to be in contact with each other.  To illustrate both of these
benefits, let’s look at a 3V microcontroller (MCU) that needs to turn on a 100V
motor.

Chances are that the MCU is on a digital ground, and the motor is on an
analog ground plane.  If you were to connect the control lines of the motor
directly to the MCU, you’d create a ground loop and ground potential difference
(GPD) that may inhibit signals from the MCU passing to the motor.  Not to
mention the connection alone might fry the MCU, but if for some reason the MCU’s
control signals make it through this GPD and turn on the motor; the back
electromotive forces (EMF) generated from the motor turning could come back and
fry the MCU altogether!   If you designed your system this way, don’t
fret… it’s not too late to isolate.  Good things take time, so don’t
misinterpret procrastination as laziness; all engineers know that truly it is
efficiency. No matter your design it’s never too late to add isolation.

Galvanic isolation comes in multiple formats as well as varying degrees of
protection. Another way to look at it would be through the eyes of Goldilocks:
one that is “just right” when others seem to be “too hot” or “too cold.”
Starting off at the most isolation protection you can get, I'll address
reinforced isolation.  You may have heard about TI’s reinforced digital galvanic isolators, announced during the
electronica trade fair in Munich.

These devices offer bulletproof ruggedized protection which is called for in
some scenarios, such as harsh industrial environments dealing with very noisy
signals that can spike up very quickly.  These might be seen as “too hot”
in the Goldilocks scenario.  Functional isolation on the other end is the
lowest form of isolation, where protection is offered but minimal levels or “too
cold,” and basic isolation is in between being not too hot and not too cold in
terms of protection, but just right.

Basic galvanic isolation covers you when you need more than “a little” but
less than “a lot” of protection in environments where things can get noisy but
not apocalyptic. For example, in any major industrial design there is most
likely a power block connected to a noisy power supply. Depending on the quality
and noise-rejection capability of that power supply (perhaps even inside it),
you’d probably want to employ a reinforced isolator, since it could deal with
the majority of the challenging electrical interference. What is then cleaned up
and passed along to be used by the system itself should be OK to use, but what
happens in theory doesn’t always translate in the real world. Thus, you might
need a little more isolation in the rest of your system. This protects against
runaway power-supply pulses or internally generated spikes from sensors or other
industrial equipment like motors, fans, servo controls and protects more
delicate microcontrollers or microprocessors or even a more costly field
programmable gate array (FPGA) or digital signal processor (DSP).

So don’t procrastinate; isolate!  Find a galvanic digital isolator that’s just right for you. In
fact, TI has a new line of basic digital galvanic isolators. Compared to our previous
generation, these capacitive-based digital isolators offer:

A 20% higher UL 1577 isolation rating of 3.0kVRMS.

50% higher DIN V VDE V 0884-10 maximum-surge voltage rating of
6kVPEAK.

80% lower active power.

If all of your galvanic digital isolators have been “too hot” and “too cold,”
perhaps you should check out TI’s line of “just right” basic digital isolators
and keep your design comfortable and covered.

Additional resources:

Check out our digital isolators portal page.

Read application notes on high-voltage test methodologies or understanding electromagnetic compliance.

Watch videos explaining more abstract concepts like common-mode transient immunity and creepage and clearance.

If you don’t see what you’re looking for, try searching for asking a question
in our TI E2E™ Community Industrial Interface forum.

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