AN165 - EMI REDUCTION TECHNIQUES

Description

Common-mode radiation is the result of undesired voltage drops due to voltage differentials in the I/O ground system.

The CS4297A clock transitions result in a rush of current that may induce the digital ground plane to "bounce".

Crystal

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Part number	AN165
Manufacturer	Crystal
File Size	58.51 KB
Description	EMI REDUCTION TECHNIQUES
Datasheet	AN165 Datasheet
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www.DataSheet4U.com AN165 Application Note CS4297A/CS4299 EMI REDUCTION TECHNIQUES 1. INTRODUCTION The CS4297A and CS4299 AC ’97 audio codecs are based on a new and faster fabrication process, and certain precautions in the analog I/O circuitry may be required to prevent 49.1 MHz commonmode radiation. Note that 49.1 MHz is 2 times the CS4297A internal clock frequency of 24.576 MHz. 3. EMI SHUNTING CIRCUIT The key to reducing common-mode emissions is to add decoupling (called shunting) at the audio I/O connectors. The shunt capacitors must be connected to a "clean" (free of digital noise) I/O ground. The recommended EMI shunting circuit is shown in the following diagram, and includes ferrite beads and 1000 pF NPO capacitors.

Published: Jan 10, 2007 |