AN-1109 Datasheet, PDF (1/20 Pages) Analog Devices – Recommendations for Control of Radiated Emissions with iCoupler Devices

AN-1109
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: [phone] • Fax: [phone] • www.analog.com
Recommendations for Control of Radiated Emissions with iCoupler Devices
by Brian Kennedy and Mark Cantrell
INTRODUCTION
iCoupler® data isolation products can readily meet CISPR 22
Class A (and FCC Class A) emissions standards, as well as the
more stringent CISPR 22 Class B (and FCC Class B) standards in
an unshielded environment, with proper PCB design choices.
This application note examines PCB-related EMI mitigation
techniques, including board layout and stack-up issues.
Several standards for radiated emissions exist. In the U.S., the
Federal Communications Commission (FCC) controls the
standards and test methods. In Europe, the International
Electrotechnical Commission (IEC) generates standards, and
CISPR test methods are used for evaluating emissions. The
methods and pass/fail limits are slightly different under the two
standards. Although this application note references IEC stand-
ards, all results are applicable to both standards.
Data transitions at the input of iCoupler digital isolators are
encoded as narrow pulses that are used to send information
across the isolation barrier. These 1 ns pulses have peak
currents of up to 70 mA and may cause radiated emissions and
conducted noise if not considered during printed circuit board
(PCB) layout and construction. This application note identifies
the radiation mechanisms and offers specific guidance on
addressing them through high frequency PCB design
techniques.
Control of emissions from signal cables and chassis shielding
techniques are outside of the scope of this application note.
EMI MITIGATION OVERVIEW
Best-practice techniques for EMI mitigation include a
combination of the use of input-to-output ground plane
stitching capacitance, edge guarding, and the reduction of
supply voltage levels for noise reduction. For the purposes
of this application note, a 4-layer board was designed and
manufactured using materials and structures well within
industry practice.
The EMI reduction examples used in this application note are
based on the 4-channel iCoupler products, but the information
is relevant to all the iCoupler product families, examples of which
are shown in Figure 1.
For information on reducing emissions from products using
isoPower, integrated isolated power, refer to the AN-0971
Application Note, which includes additional recommendations
and techniques.
ADuM14xx, ADuM24xx,
ADuM34xx, ADuM44xx,
ADuM744x
ADuM13xx, ADuM33xx
ADuM12xx, ADuM22xx,
ADuM32xx
ADuM1100, ADuM3100
Figure 1. Example of iCoupler Device Families
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