AN2321 Freescale Semiconductor / Motorola, AN2321 Datasheet - Page 9

• Manufacturer Part Number: AN2321
• Description: Designing for Board Level Electromagnetic Compatibility
• Manufacturer: Freescale Semiconductor / Motorola

MOTOROLA
There are two types of core material for the inductor: iron and ferrite. Iron core
inductors are used for low frequency applications (tens of kHz) while ferrite core
inductors are used for high frequency applications (to MHz). Therefore, the
ferrite core inductor is more suitable for EMC applications.
There are two special types of inductor that are used specifically in EMC
applications: ferrite beads and ferrite clamps.
The ferrite bead is a single turn inductor and is usually a single lead through the
ferrite material to form the one turn. This device provides 10dB attenuation over
the high frequency range, and a low attenuation at DC.
Similar to the ferrite bead, the ferrite clamp provides 10 to 20dB attenuation in
both common mode (CM) and differential mode (DM) in the higher MHz region.
In DC-DC converter applications, the inductor must have low emissions and be
able to handle high saturation currents. Based on these requirements, the
bobbin shape inductor has these characteristics to fit this application. In power
supply applications, a LC filter is needed to provide impedance matching
between low impedance supply and high impedance digital circuit. The circuit
shown in
One of the most popular use of the inductor is in the AC mains filter, as shown
in
Designing for Board Level Electromagnetic Compatibility
Figure
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 6
7.
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LOW IMPEDANCE
POWER SUPPLY
can be used.
PART 2: COMPONENT SELECTION AND CIRCUIT DESIGN TECHNIQUES
L
N
C
X1
Figure 7. AC Mains Filter
Z
Figure 6. LC Filter
HI
L1
C
C
X2
Z
LO
C
C
Y1
Y2
HIGH IMPEDANCE
DIGITAL CIRCUIT
L
E
N
AN2321/D
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