Application Note
AN-1109
SOURCES OF CONDUCTED NOISE
Large currents and frequencies also generate conducted noise
on the ground and power planes. This can be addressed with
the same techniques for radiated emissions because the causes
and remedies for both types of EMI can be improved with the
same PCB ground and power structures.
tude of 70 mA. An ideal bypass capacitor of 100 nF should be
adequate to supply the ac component of the current. However,
bypass capacitors are not ideal and may connect to the ground
or power planes through an inductive via. In addition, a large
distance between ground and power planes creates a large
inductance between them, which restricts the ability to supply
current quickly. These factors may contribute to a large fraction
of a volt of high frequency noise on the VDD plane.
The inability of the bypass capacitors and ground/power planes
to provide adequate high frequency current to the iCoupler
device causes VDD noise. The iCoupler isolator transmits data
across the transformer in bursts of 1 ns pulses with an ampli-
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