Recommendations for Control of Radiated Emissions with iCoupler Devices
News Release from:
26 May 2011
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.