DP83TD510E: Using with unbalance 50ohm cable

Hello Shiraki-san,

Would it be possible to ask for a drawing of what is going on? I'm afraid I am not understanding how the 25ohm, 50 ohm and balun are interacting with each other.

Sincerely,

Gerome

Sorry for made you confuse.

I'm thinking below Case A.

I think the ideal design in this case would be Case B, but I could not found good candidate of a balun.

To get balanced, I'm thinking to change the two resistors on Tx to 25ohm.

Hi Shiraki-san,

Referencing section 8.2.1.1 of the DP83TD510E datasheet, you are saying that RTX1 and RRX1 (as well as RRX2 and RTX3) are all 25Ohms?

Sincerely,

Gerome

Hi Gerge-san,

Becasue RRX1 and RRX2 are for input, and input impedance of RX+/- should be big enough, they were not discussed here.

I just focused on those values that impact signal transmittion, impedance maching.

Just use RTX1/2 25ohm instead of 50ohm, others remain the suggested value in detasheet.

Regards,

Shiraki

Hi Shiraki-san,

You are saying if RTX1 and RTX2 are 25 ohm rather than 50 ohm, however, this doesn't match your picture you provided. Wouldn't in your case RTX1, RTX3 = 25 ohm, RRX1, RRX2 = datasheet value, and RTX2, RTX4 = short? Please advise. Maybe a table such as Table 8-1 or a figure with all resistances like Figure 8-2 might make everything clearer.

Sincerely,

Gerome

Gerome-san

Sorry for my typo.  not RTX1/2 but RTX1/3.

When you see the Figure 8.2.1.1 on the datasheet,

RTX1+RTX2 is 25ohm (Originally 50ohm)

RTX3+RTX4 is 25ohm (Originally 50ohm)

It is to reflection when using unbalanced 50ohm coax. cable with 1:1 balun.

If the mixed resister value  should not be such small value,

then I will consider uisng 1:2 balun and use bigger resisters.

Regards,

Shiraki

Shiraki-san,

From team, "Our transmitter design in DP83TD510LR cannot support Case-A shown from the query on E2E."

Sincerely,

Gerome