Specifications

104 Control and Automation Solutions Guide
once the PD is removed. The PSE must
also protect the cable and the PD from
overcurrent and short-circuit conditions.
These protections in PoE provide unique
safety and power-savings capabilities.
PoE is becoming an option in a growing
number of industrial applications due
to new computing devices, lighting,
sensors, and user-interface units all
declining in power consumption.
Furthermore, PoE standards are being
expanded to support high power levels.
By integrating all required functions,
the Maxim PSE controller MAX5980
makes designing PSE systems simple,
compact, and cost eective. PD
equipment design is likewise simplied
by the use of the MAX5969D.
PoE Specifics
Topology: Point-to-point
Maximum power at PD input: 12.95W
of 3af standard, 25.5W of 3at standard,
up to 100W of nonstandard
Data rates: Compatible with
standard Ethernet data rates
Distances: 100m
Standards: IEEE
®
802.3af, IEEE 802.3at
For more information, go to: www.
maxim-ic.com/power-over-Ethernet.
Wireless Systems
In certain BASs it is simply not
feasible to run wires to establish a
communications link. The rst two
considerations in choosing the RF link
technology are the link distance and the
required data load. There are additional
considerations, such as whether the
communications can be one-way or
two-way. Some applications such as
video security, to be implemented
wirelessly, require relatively high data
rates and constant transmission. Other
applications have very low data loads
and require only periodic transmissions.
Systems that detect room occupancy
are an example. Since channels handling
low data loads use much less power
than those with high data load, they can
often be implemented using battery
power while realizing manageable
battery life. It is also possible to harvest
energy from unconventional sources
and use rechargeable batteries, thereby
greatly reducing maintenance.
In home applications, distances are
not usually very far and may be low
data load, so radio power levels can
be low. In large buildings, however,
the distances become signicant
and the data load increases, so the
capabilities of the wireless system
must be greater. Maxim has a wide
variety of radio technologies that solve
unique engineering challenges and a
high-frequency ASIC group that works
with customers to develop proprietary
solutions. For more information,
go to: www.maxim-ic.com/asics.
Before discussing the wireless interfaces
specically, let us briey explore the
motivations behind implementing
wireless communications. Why wireless,
if it is fraught with problems?
Problem 1: Power. If you install a
wireless link, you need to power
both devices, so you need a remote
power source. However, your main
motivation for using a wireless link
was probably to avoid wires, so
unless there is a nearby power outlet,
you need to rely on batteries.
Problem 2: Link range.There is
no guarantee that the link will
be established or be error-free
because of EMI/RFI, walls with metal
structure, or equipment blocking
the signal and limiting the range.
Problem 3: Data security. Unless
directional antennas are used,
the information spreads out in all
directions for anyone to pick up if
they have the right equipment.
Despite the problems, there are
signicant benets to using a wireless
link with solutions to these problems.
Benet 1: Ease of installation and
modication. It is much easier (and
probably cheaper) to install a stand-
alone module than it is to run wires
through walls or in ceilings; when
the system needs to be expanded
or modied, it is simple to do.
Benet 2: Enables mobile applications.
Benet 3: Enables a communication
link across a barrier that is impossible
to puncture with wires that would
compromise the structure’s integrity.
Let us address the rst problem, power.
In the case of a low data load application,
one can avoid periodic battery
replacement using Maxim’s energy-
harvesting technology (MAX17710)
that can extract energy from a variety
of sources such as light, vibration,
thermoelectric, radio frequency
energy, and varying magnetic elds.
It manages the charging of a battery,
a super capacitor, or microenergy cell.
To get enough voltage for the battery,
it boosts the voltage from low-voltage
sources as low as 0.75V and it handles
high-voltage sources up to 5.7V. It also
protects the battery from overcharging
and overload. Of course this energy-
harvesting capability is not viable unless
the average load on the battery is less
than the energy available. Maxim has
made signicant progress reducing
power waste in our radio solutions.
In typical security applications, the
radio transmits only periodically, and
between transmissions enters sleep
mode where power consumption is
nearly zero. Therefore, if one were to
use primary cell batteries needing
periodic replacement, Maxim’s radios
help to extend the life of those batteries,
or if using an energy-harvesting
approach, can make it workable.
The second problem is link range. This
is a fundamental task for all installers
of radio links, to perform “link budget”
analysis. All gains and losses from
the transmitter to the receiver are
considered and the nal system must
include some margin to assure reliable
results. Several variables can be adjusted
to achieve a successful outcome.