T1 Transformer Ratios

Jun 18, 2006 3 Replies

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jai.dhar 20 years ago

Hello,

I'm trying to design a circuit with a T1 interface chip, magnetics and RJ45s. I'm having trouble deciding on which magnetics to use. How do I determine what the pri:sec ratios should be? Is this dependant on the T1 interface chip? The datasheet for the interface chip says 1:1 for RX, and 1:2 for TX, but I was wondering what would happen if I used a

1:2 for RX as well? The reason I ask is because I would like to use the magnetics from Pulse Engineering that have integrated IC-side protection, and for some reason, they only come in 1:2 ratios. I was hoping to gain a better understanding of what determines these ratios. I know how transformers work in general, but what is it that determines whether I need a 1:2, 1:1.2 etc...

Thanks,

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Don Bowey 20 years ago

If by T1 you mean a DS1 rate (1.544 MB/s) then the line impedance is 110 Ohms. Also, RJ48 is the wrong pinout. Use RJ48-C.

Don

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jai.dhar 20 years ago

Thanks for the reply Don..

I thought it was RJ45, but you mentioned RJ48-C. In terms of the physical jack, they are the same thing, no? As in they are both 8-pin modular jacks with the same dimensions and orientation for Pin 1?

Regarding line impedance, how does this affect my transformer ratio? I'm still not sure how to settle on a transformer to use.

D> On 6/18/06 9:33 AM, in article

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Don Bowey 20 years ago

Yes, the physical jack is the same for RJ45 and RJ48C, but the pin assignments differ.

You did not mention the IC you are using or what you are building; whether the interface is DSX-1 or a 30 dB line. The datasheet for the device should give you the insight you require. If this is for a commercial product, I'd follow its recommendation?

Don

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