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Eliminate ground loops, which are unexpected current return paths to the power source and ground.
Decouple the telephone line cables at the telephone line jacks. Typically, use a combination of series
inductors, common mode chokes, and shunt capacitors. Methods to decouple telephone lines are similar to
decoupling power lines; however, telephone line decoupling may be more difficult and deserves additional
attention. A commonly used design aid is to place footprints for these components and populate as
necessary during performance/EMI testing and certification.
Decouple the power cord at the power cord interface with decoupling capacitors. Methods to decouple
power lines are similar to decoupling telephone lines.
Locate high frequency circuits in a separate area to minimize capacitive coupling to other circuits.
Locate cables and connectors to avoid coupling from high frequency circuits.
Lay out the highest frequency signal traces next to the ground grid.
If using a multilayer board design, make no cuts in the ground or power planes and be sure the ground
plane covers all traces.
Minimize the number of through-hole connections on traces carrying high frequency signals.
Avoid right angle turns on high frequency traces. Forty-five degree corners are good; however, radius turns
are better.
On 2-layer boards with no ground grid, provide a shadow ground trace on the opposite side of the board to
traces carrying high frequency signals. This will be effective as a high frequency ground return if it is three
times the width of the signal traces.
Distribute high frequency signals continuously on a single trace rather than several traces radiating from
one point.
Electrostatic Discharge Control
Handle all electronic devices with precautions to avoid damage due to the static charge accumulation.
See the ANSI/ESD Association Standard (ANSI/ESD S20.20-1999) – a document "for the Development of an
Electrostatic Discharge Control for Protection of Electrical and Electronic Parts, Assemblies and Equipment." This
document covers ESD Control Program Administrative Requirements, ESD Training, ESD Control Program Plan
Technical Requirements (grounding/bonding systems, personnel grooming, protected areas, packaging, marking,
equipment, and handling), and Sensitivity Testing.
MultiTech strives to follow these recommendations. Input protection circuitry is incorporated in MultiTech devices
to minimize the effect of static buildup. Take precautions to avoid exposure to electrostatic discharge during
handling.
MultiTech uses and recommends that others use anti-static boxes that create a faraday cage (packaging designed
to exclude electromagnetic fields). MultiTech recommends that you use our packaging when returning a product
and when you ship your products to your customers.
QuickCarrier™ USB-E MT100UCC-EV3 Developer Guide
DESIGN CONSIDERATIONS
7
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