TLK1501 Recommended Rref Value

Carson Hammoser1

Other Parts Discussed in Thread: TLK1501

What is the recommended Rref for the TLK1501 to a 100ohm optical transceiver? The datasheet only mentions 50R and 75R impedances.

over 12 years ago

0 Michael Peffers over 12 years ago

TI__Mastermind 20820 points

Hi Carson,

We specify the Rref value in the data sheet to set the output swing of the TLK1501 for 50ohm and 75ohm cabling environments. Can you provide me with the data sheet for your optical module so that I can examine the specs for the outputs on it?Also, what are you driving with the module? A backplane?

Regards,

Mike

0 Carson Hammoser1 over 12 years ago in reply to Michael Peffers

Prodigy 90 points

Hi Mike,

I'm interfacing to a Firecomms Gigabit GDL1000T transceiver (new p/n is FB01GKVR which I've attached 1108.FB01GKVR_Data_Sheet.pdf).

I'm not driving a backplane, but using the SERDES link to control and read some SPI based ADCs and DACs. (On the other side of the connection we're interfacing to the same Gigabit transceiver with an FPGA.)

Thanks,

Carson

0 Michael Peffers over 12 years ago in reply to Carson Hammoser1

TI__Mastermind 20820 points

Hi Carson,

Are you AC coupling in your design?

Regards,

Mike

0 Carson Hammoser1 over 12 years ago in reply to Michael Peffers

Prodigy 90 points

Hi Mike,

Yes I am AC coupling.

Also a related question, are the design files/gerbers for the TLK1501 EVM available? I realise that there is a layer printout in the documentation, but it's usually easier to follow look at an electronic version.

Thanks,

Carson

0 Michael Peffers over 12 years ago in reply to Carson Hammoser1

TI__Mastermind 20820 points

Hi Carson,

The Rref that should get you in the range of your optical modules input differential voltage is going to be in the range between 325 to 370 ohms. You will have to try a couple values to find the spot that you are looking for.

The TLK1501 is a CML driver and your optical module is an LVDS receiver so you will have to add some additional biasing to interface the two devices. Please refer to the app note "Interfacing Between LVPECL, VML, CML, and LVDS Levels" on the TI website at: http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slla120.

I am in the process of locating the Gerber's for that EVM board now and I will post them here when I find them.

Regards,

Mike

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TLK1501 Recommended Rref Value