5 Things You Need To Know When Selecting Ethernet Magnetics: Page 2 of 2

October 11, 2016 //By EDN Europe
By Adam Chidley, Avnet Abacus
Magnetics are Not Optional
design is battery powered, do also check the insertion loss at different frequencies for an indication of how much energy will be wasted in the modules. And finally, different modules also have different operating temperature ranges for different applications.

The market leader for ICMs is Bel Stewart’s MagJack range, which comes in 10/100Base-T to 10GBase-T and PoE (plus) versions

 ICMs Suit (Almost) Every Application

ICMs are a great option for the majority of systems, as they maximise the available space, boost reliability and minimise component count. There are many products available in various configurations, including single and double row ganged modules, SMT and USB-combination products. While the density of these products is steadily increasing, this can have unintended effects on crosstalk between channels, as the magnetics are smaller and everything is closer together. Be sure to select a connector with adequate shielding to keep crosstalk to a minimum. In terms of layout, PCB traces between the transceiver and the ICM should be kept as short as possible to avoid the effects of EMI, though be aware that this may result in a tradeoff with ESD protection.

PoE Places Additional Demands on Magnetics

Power over Ethernet (PoE) places additional demands on the magnetics in terms of performance and isolation, since currents are much higher. Both discrete magnetics modules and ICMs come in versions specially designed to deliver the right current for PoE and PoE+ designs.

Some PoE ICMs also integrate PoE controller ICs as well as magnetics for a drop-in solution that manages the communications between powered devices and the switch or router, as well as handling safe power up and power down of the powered device. These types of products don’t require any further PoE circuitry on your board, great if you’re short of space, or design time.

As a power device, a PoE ICM requires more EMI shielding than other ICMs to protect against unwanted emissions. They may also require additional thought in terms of thermal management, especially in applications that experience wide temperature ranges with only passive airflow.

For more on magnetics and other passive technologies visit Engineers’ Insight , a technical blog from Avnet Abacus.

Adam Chidley, Senior Product Manager Passives - EMEA, Avnet Abacus

For almost 10 years Adam Chidley has worked at Avnet with line responsibility for several key suppliers and technologies across the Group.  His previous experience was in contract manufacturing and for component manufacturers in this market, giving him a broad knowledge from concept to production.

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