if the ratio's difference of the transformer will make any difference to the PHY's work

Hello,

Applications Note AN-1469 (page 14) lists the necessary turns ratio of the magnetics as 1:1.

Proper operation of the DP83849I can not be guaranteed if magnetics are used which

do not meet the recommended specifications.

Thanks,

John

Hello,

Thank you very much for answering my question.

But I still wanner know how the ratio will affect the PHY's work.

 Here is the situation: in my applicaton with 1.414:1, the PHY and the transformer are on two boards, and the DP83848I is used to take the place of another PHY, which works with 1.414:1 properly. So I wanner know if I can use DP83848I here or not. This is important to me, because there are a few other boards with transformer-1.414:1, and a few other boards with the former PHY-1.414:1.

Thanks,

Lin Ding

Hello,

What is the manufacturer / part number of the 1.414:1 transformer?

What is the manufacturer / part number of the phy that 'works properly' with the 1.414:1 ratio transformer?

How do you define "works properly', do you mean that the phy links and transmits data at both data rates,

that the waveforms conform to IEEE 802.3 standards?

Thanks for the additional information.

John

Hello,

First, I wanner apologize that the ratio is 2:1, not 1.414:1.

The PHY is LXT905, and the transformer is ST4202. According to their datasheets, the work ratios are 1;1 and 2:1.

Speaking of "works properly", I think we have come to the point. In fact, I'm confused the relationship between "waveforms conform to IEEE 802.3 standards" and "links and transmits data at both data rates".

So far, in one of my applications, DP83848I has taken the place of LXT905, and links and transmits data at 10Mbps some how well. But since the work ratios are not very meet the datasheet, I'm afraid that there will be a trap or a collapse waiting for me.

Thanks for the patience.

Lin Ding

I am not sure I understand the full configuration.  It sounds like one end of the link is a DP83848 that connects to the Ethernet cable via a transformer with a 2:1 ratio.  Is that correct?  Is the 2x coil on the device side or the cable side? 

What is on the other side of the cable?  Is it a board of the same configuration or a board of a different design? 

Patrick

Helllo Patrick,

First, what I said was all about one end of the link.

In the paticular application, DP83848 connects to ethernet cable via a 1:1 RX ratio and a 2:1 TX ratio, due to the former PHY's datasheet. And the ratios cann't meet DP83848's datasheet.

The other side of the cable could be any device, a board of the same configuration, a board of a different design or even PC.

Thanks,

Lin Ding

Understood.  For the TX transformer, the signal levels transmitted by the DP83848 incorrect by a  two due to the 2:1 transformer.  This will result in signal levels on the Ethernet cable that are well outside the IEEE specifications.  When the signals arrive at a device or PC on the other side of the Ethernet cable, they will likely be rejected.  It may work under some limited conditions, but will likely fail for most applications.  I would strongly recommend using 1:1 transformers for both the TX and RX paths.

Patrick