Technology
Electromagnetic Interference in
Switching Converters
Migrating from Linear regulators to switching converters can be a nightmare for
system architects especially working in the automotive and avionics market
segment. They are aware of the “EMI risk” and the consequences on the product
design cycle. But due to a higher efficiency demand and a smaller footprint they are
forced to think about switching converters.
This article presents a basic view of the cause of EMI in switching converters, best
designs practices that can mitigate EMI and an example of a real system.
Akshat Garg, Analog Applications Engineer, Texas Instruments Incorporated
Electromagnetic Interference
The dI/dt and dV/dtproblem!
A magnetic field produced by the changing current in one
conductor (source) will induce a voltage in another (victim)
according to e = M • di/dt ; where M is the mutual inductance
between the source and victim.
This principle is used to explain the working of transformers.
However it is applicable to any system. The induced voltage can
add additional stress on components and needs to be accounted
for. As an example, consider a multi- layer PCB. Changing currents
(di/dt) on a layer can induce voltage on the other layers due to
the mutual inductive coupling between layers. This coupling is a
result of the long return current path for each layer.
To reduce the effect, layers are separated by ground planes. In a
properly designed layout, the ground plane will provide the
shortest (lowest impedance) path for the return currents and
thereby reduce the Inductive coupling between layers.
An electric field produced by thechanging voltage on a surface of
a conductor (source) will induce a current to flow in another
conductor (victim) according to i = C• dv/dt; where C is the
ELE Times | 51 | November, 2016