EMC Design Guide for Printed Circuit Boards
Frame 67 of 78
Printed copies are uncontrolled
86. Coaxial cable should be used for transmission of RF (above 10 MHz) and where
impedance match over a broad frequency range is important (such as video
87. Circuits generating large, abrupt current variations should be provided with a separate
return lead to the ground in order to reduce transient pickup in other circuits.
88. All unused multipurpose Integrated Circuit (IC) ports should be configured as outputs
to prevent unintentional random state switching and noise generation i.e.
unterminated CMOS inputs tend to self-bias into the linear region of operation, thus
significantly increasing DC current draw. Use appropriate pull-up or pull-down
discrete components. Consult IC manufacturer for recommendation.
89. Software may be used to disable (turn off) all unused clock outputs from an IC.
Consult IC manufacturer for recommendation.
90. Reducing output buffer drive from IC's may reduce radiated emissions. Consult IC
manufacturer for recommendations.
91. All output drivers should be protected against flyback transient from inductive loads.
92. ESD sensitive devices should never be located close to I/O connectors or any other
accessible openings where they may be damaged by an ESD event.
93. Keep ribbon cables and jumper strips away from IC's and oscillator circuits. Routing
over or near IC's should be avoided at all cost (Figure 520).
Figure 520. Packaging Considerations Affecting RE and CE