Curtis 1356, Manual, Page: 55 / 58

Curtis 1356 /1356P CAN Expansion Module Manual,
Rev. A
A-1
APPENDIX A
DESIGN CONSIDERATIONS
ELECTROMAGNETIC COMPATIBILITY (EMC)
Electromagnetic compatibility (EMC) encompasses two areas: emissions and
immunity. Emissions are radio frequency (RF) energy generated by a product.
This energy has the potential to interfere with communications systems such
as radio, television, cellular phones, dispatching, aircraft, etc. Immunity is the
ability of a product to operate normally in the presence of RF energy. EMC
is ultimately a system design issue. Part of the EMC performance is designed
into or inherent in each component; another part is designed into or inherent
in end product characteristics such as shielding, wiring, and layout; and, finally,
a portion is a function of the interactions between all these parts. The design
techniques presented below can enhance EMC performance in products that
use Curtis control products.
Emissions
Signals with high frequency content can produce significant emissions if con-
nected to a large enough radiating area (created by long wires spaced far apart).
PWM drivers can contribute to RF emissions. Pulse width modulated square
waves with fast rise and fall times are rich in harmonics. (Note: PWM drivers
at 100% do not contribute to emissions.) The impact of these switching wave-
forms can be minimized by making the wires from the controller to the load as
short as possible and by placing the load drive and return wires near each other.
For applications requiring very low emissions, the solution may involve
enclosing the system, interconnect wires and loads together in one shielded
box. Emissions can also couple to battery supply leads and circuit wires out-
side the box, so ferrite beads near the controller may also be required on these
unshielded wires in some applications. It is best to keep the noisy signals as far
as possible from sensitive wires.
Immunity
Immunity to radiated electric fields can be improved either by reducing overall
circuit sensitivity or by keeping undesired signals away from this circuitry. The
controller circuitry itself cannot be made less sensitive, since it must accurately
detect and process low level signals from sensors such as the throttle potenti-
ometer. Thus immunity is generally achieved by preventing the external RF
energy from coupling into sensitive circuitry. This RF energy can get into the
controller circuitry via conducted paths and radiated paths. Conducted paths
are created by the wires connected to the controller. These wires act as antennas
and the amount of RF energy coupled into them is generally proportional to
their length. The RF voltages and currents induced in each wire are applied to
the controller pin to which the wire is connected.
APPENDIX A: EMC & ESD DESIGN CONSIDERATIONS