# Ethernet magnetics selection guide

Status
Not open for further replies.

#### myatham

##### Member level 3
Hello,
I need select a ethernet magnetics for my application of 10/100BaseT.

Please suggest me how to start the magnetics selection and what are the parameters that are to be considered whiel selecting magnetics?

When do we use 1.25:1 magnetics instead of 1:1 magnetics?

When do we use RJ45 connector with integrated magentics and when do we use stand alone magnetics?

#### HMS1021

##### Full Member level 2
"When do we use 1.25:1 magnetics instead of 1:1 magnetics?"
Nearly everything today is 1:1. The 1.25 and 1.41:1 were rare and related to 10T. For 10/100 stay with 1:1

"When do we use RJ45 connector with integrated magentics and when do we use stand alone magnetics?"
The most common approach is integrated magnetic. Standalone magnetics seem to occupy the ends of the cost line. There are people that try to save penny's by using discrete parts in place of an integrated solution and at the other end some military and space customers feel a integrated hybrid for the magnetics and a connector which is just a connector are more reliable with better performance, and justifies the added costs.

So, pick a 1:1 10/100 device based on price and features such type of board mounting and LEDs if you need them.

I have been using the TE Connectivity 5-6605435-8. It is a 10/100/1000 RJ-45 with 2 LEDs built in. I believe a GBE ready connector is very well built and will exceed my 100T requirement with a wide margin. I build custom systems 1 or 2 at a time so a few extra  isn't a driver for me and if it saves me from having a problem in test it is worth it. It also means I design in and stock the same part for boards with GBE.

#### diggdip

##### Newbie level 5
Hi,

Does any one know a good source to learn how to select the correct magnetics?
Say i want to improve EMC issues (emission and immunity) using better integrated RJ45, what should i choose?
What is the better placement of CMC, since there are various combination on the TX/TX ports?
When should i use use the 5 or 7 pole filters integrated?
I saw that GbE uses 2 CMC chip side and cable side, is it a GbE requirement, can it work better for the EMC in case of 10/100 T-base?