November 2015
22
I
ndustrial
C
ontrol
& C
ommunications
the microcontroller. This approach is costly
in parts count, board space, and use of dig-
ital I/O pins. Today, multichannel serializers
like the MAX31911 can translate, condition,
and serialize the 24V digital outputs of sen-
sors and switches to the 5V, CMOS-compat-
ible levels required by PLC microcontrollers.
This approach reduces the necessary num-
ber of isolated channels to just three. The
MAX31911, for example, is an 8-channel
industrial interface that supports SPI daisy
chaining; larger numbers of inputs from mul-
tiple serializers can share the same three iso-
lated signals. It enables dramatic savings in
power dissipation, parts count, overall PCB
real-estate footprint, optocouplers, and cost
for a 32-channel implementation.
Higher I/O density and smaller form factors
also add to the design challenge in another
basic way, a consequence of the inevitable
power dissipation. The system must be more
power efficient than ever to keep the PLC from
overheating, especially in an application where
fans and vents are generally not acceptable. An
often overlooked source of heat in PLCs is I2R
losses in the DC power-distribution feeds. Fre-
quently, 24V is used for PLC backplanes, while
12V is used for on-board distribution. A bet-
ter approach is to use 48V across the board, as
this reduces currents by a factor of 4 and, cor-
respondingly, PCB copper losses by a factor of
16. Using high-voltage point-of-load (POL)
DC-DC converters like the MAX17503 elimi-
nates the need for an intermediate DC-DC con-
version stage. These converters operate directly
with up to 60V inputs to enable single-stage
conversion for digital, analog, and mixed-sig-
nal loads at low voltage. The converters free
valuable board space while avoiding the cost
and energy losses of the interstitial stage. Addi-
tionally, they minimize copper losses, reduce
connector contact current ratings, increase
reliability, and maintain cool operation (typ-
ically 50% cooler) due to their synchronous
switch architecture.
Today signal-conditioning, processing, and
communication circuits require a diverse set
of power rails, often differing by a few volts
or only fractions of a volt. This exacerbates an
already complex electrical environment. Add
to this, the increasingly sophisticatedmethods
of energy savings through various power-con-
trol methods and the cost and complexity of
power subsystems only increase further. The
Beyond-the-Rails-products from Maxim sim-
plify the signal chain, enabling a design that
allows ±10V bipolar inputs to be multiplexed,
amplified, filtered, and digitized, all with a
single 5V supply. This approach eliminates
the need for additional ±15V power supplies,
thus reducing component count, system cost,
power dissipation, and footprint.
When factory networks were closed to the
outside, IT security issues usually involved
rogue employees and internal data theft.
Those good old days are gone and not com-
ing back. Today Internet-connected PLCs
must be protected against multiple threats,
including hackers, malware, and viruses. Sys-
tem-level software provides an initial level
of protection, but in many cases this is not
enough. Hardware-based security is needed to
protect against the following threats. Cloned
or counterfeit components: Counterfeit field
sensors and I/O modules pose a real threat to
your bottom line. But there is a bigger danger:
counterfeit field sensors could be used to exe-
cute an attack on the industrial environment.
Using a secure authentication IC is the only
way to guarantee that you can trust the sen-
sor readings sent from critical components to
the PLC.
Malware injection: Stuxnet was a wake-up
call to industry. System operators must ensure
that all equipment upon which a supervisory
control and data acquisition (SCADA) or dis-
tributed control system (DCS) is built runs
genuine software. Secure boot and secure
update management are the best ways to pro-
tect a device frommalware injection. A secure
coprocessor can be used to implement an
encryption design that fully addresses these
issues with minimal design-in effort.
Eavesdropping: As concern over industrial
espionage increases, manufacturers must
ensure that unauthorized users cannot steal
trade secrets off industrial networks. Encryp-
tion and authentication ICs can protect
against such eavesdropping, and go further
with active tamper detection to prevent brute-
force attacks on the hardware components.
Maxim has a rich history in hardware secu-
rity implementation for ATMs, point-of-
sale (POS) systems, and consumables such
as printer cartridges. The security product
portfolio ranges from simple authentication
engines to complex, secure microcontrollers
that implement advanced standards-based
encryption algorithms.
Industry 4.0 is fundamentally transform-
ing what it takes to win in the PLC mar-
ket. Smaller form factors, higher I/O density,
and advanced capabilities - success today
demands new strategies for managing com-
peting demands for more functions in less
space. This problem will not be solved by
Moore’s law. The large amount of analog con-
tent in these systems means that PLC engi-
neers can no longer ignore the integration
problem in front of them. Not when success
depends on how much functionality you can
pack into every centimeter of space. Engi-
neers who systematically seek higher levels of
component integration will be well positioned
as manufacturers pursue the benefits prom-
ised by Industry 4.0.
n
Figure 4. 60V synchronously rectified Maxim DC-DCs like the MAX17503 greatly reduce heat,
size, and component count.
