DS90UB925Q-Q1: Choke on FPD-LINK III differential lines

JPAlleyne

Expert 1565 points

Part Number: DS90UB925Q-Q1

Hi,

I've noticed in the EVM schematic that there is a 90 ohm choke on the FPD-LINK III lines.

1) Is this required?

2) What is its exact purpose? Blocking higher frequencies? Impedance Matching?

3) Should I be pushing to add this to my design?

Thanks,

over 6 years ago

0 Radio-Joe over 6 years ago

TI__Mastermind 37500 points

Hello

The FPDLink outputs aer AC coupled, then sent through a Common Mode Choke.

1) The Common Mode Choke is used to reduce Common Mode intererence. It is a recommended components.

We have found it helpful, in meeting Conducted Emission and Radiated Immunity testing.

Here is a reference.

https://www.murata.com/~/media/webrenewal/products/emc/emifil/knowhow/26to30.ashx

2) The exact purpose is to attenuate common mode signals between DOUT+ and DOUT- in the Forward Out or Backchannel In.

3) it is suggested for new designs.

Regards,

Joe Quintal

0 JPAlleyne over 6 years ago in reply to Radio-Joe

Expert 1565 points

Thank you for your help Joe.

JP

0 JPAlleyne over 6 years ago in reply to JPAlleyne

Expert 1565 points

Any suggestions for choosing a part? Should I ensure that the impedance for the differential signal is a 100 ohms at the operating frequency of the FPD-LINK signal?

I'm currently looking at this part: https://www.digikey.com/product-detail/en/wurth-electronics-inc/7442335900/732-5622-1-ND/4865479 due to size restrictions.

0 Radio-Joe over 6 years ago in reply to JPAlleyne

TI__Mastermind 37500 points

Hello,
I looked for differential 90 ohm common mode chokes, I see Murata, TDK, Coilcraft. I would look for the EVM part# first, then look for critical characteristics, for a similar part.
Regards,
Joe Quintal

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DS90UB925Q-Q1: Choke on FPD-LINK III differential lines