DP83848-EP: MDIO and MDC Signals - Characteristic Impedance

Tanay Ghose

Part Number: DP83848-EP

The DP83848 has Application Note AN-1469 which covers its layout guidelines.

In Section 5, it is mentioned that the MII Signals shall have 68Ω characteristic impedance (which is in compliance with the IEEE 802.3u standard). However, I was unable to find any recommendations for the characteristic impedance for the Station Management Signals (MDIO and MDC). Is there any such recommendation for these signals from TI ?

over 4 years ago

0 Lysny Woodahl over 4 years ago

TI__Expert 3595 points

Hi Tanay, is the above not the information you were looking for?

Thanks,

Lysny

0 Tanay Ghose over 4 years ago in reply to Lysny Woodahl

Prodigy 180 points

Hi Lysny,

I believe MDI in this context means Media Dependent Interface (which includes the TD/RD Differential Pairs). However, MDIO (Management Data I/O) and MDC (Management Data Clock) are what the IEEE 802.3u standard calls STA (Station Management Lines).

Thus, I think the screenshot which refers to "MDI signal traces should have 50 ohm to ground or 100 ohm differential controlled impedance" does not explicitly cover the MDIO and MDC signals. Please correct me if I am wrong.

0 Lysny Woodahl over 4 years ago in reply to Tanay Ghose

TI__Expert 3595 points

Hi Tanay,

My apologies, you are correct. I have copied the recommendation from the datasheet. It is similar to most serial interfaces, where the data lines requires a pull-up, and the clock line should not require any adjustments.

Thanks,

Lysny

0 Tanay Ghose over 4 years ago in reply to Lysny Woodahl

Prodigy 180 points

Hi Lysny,

I did see the recommendation for pull-up resistance. However, I am enquiring about the characteristic impedance of the tracks in layout.

0 Lysny Woodahl over 4 years ago in reply to Tanay Ghose

TI__Expert 3595 points

Hi Tanay,

For low speed signals like these, there are no characteristic impedance recommendations.

Thanks,

Lysny

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DP83848-EP: MDIO and MDC Signals - Characteristic Impedance