Hi, Yes , if you use transformer, you need to avoid any plane & signal under the transformer. Because transformer will induce the magnetic coupling - noise to under any signal/ plane/copper. If you use transformer integrated RJ45, Normally the connector will be shielded. so no need to provide the void. Please look the datasheet of part. Datasheet will have the internal circuit also. Regards Karthik -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Tesla Sent: Friday, December 23, 2011 8:09 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Why"Void power and ground planes under discrete magnetic components" Hi, expert i recently read a ti doc about ethernet pcb layout. http://www.ti.com/lit/an/snla107/snla107.pdf There was a setence on page 7"Void power and ground planes under discrete magnetic components." Can somebody explain why TI recommand to do like that? Now, we often use tranformer integrated RJ45, how we do about this on the PCB? Must we create a void on power and ground plane on PCB if there is a transformer?(eg,a switch power transformer?) Merry xmas Thank you ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu Please do not print this email unless it is absolutely necessary. The information contained in this electronic message and any attachments to this message are intended for the exclusive use of the addressee(s) and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately and destroy all copies of this message and any attachments. WARNING: Computer viruses can be transmitted via email. The recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email. www.wipro.com ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu