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TLK2501EVM: TLK2501 to FPGA compatibility

Moral Assraf
Prodigy 205 points
Part Number: TLK2501EVM
Other Parts Discussed in Thread: TLK2501

Tool/software:

Hi Team,

I'm connecting TLK2501EVM to and FPGA with the following DC and AC characteristics:

In the picture above the relevant info is DVPPOUT (800mV) and the common mode output (DVPPOUT/2 = 400mV)

The TX of the FPGA above is connected to the RX of the TLK2501EVM (RXP and RXN --> DINRXP and DINRXN)

Which according to the datasheet:

Seems to be ok when considering that the Tx is 800mV diff and the RX here is minimum 200mV diff. 
When looking on the common mode I'm a little bit confused, in the EVM there is AC coupling and then termination to VADD2 as seen in the second attached picture, I suppose it is adding DC level of 1.5V as recommended in the datasheet of TLK2501 but not too sure.
Please advise if any you see any violation or fault here.
If additional information is needed please let me know.

Thanks,
Moral.

  • 0
    TI__Mastermind 35903 points

    Hi Moral,

    We're reviewing this and will get back to you shortly.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Prodigy 205 points

    Hello Drew,

    This matter is of great importance to us, and we kindly request that you keep us informed of any updates.

    Thanks,

    Moral.

  • 0 in reply to Moral Assraf
    TI__Mastermind 35903 points

    Hi Moral,

    Apologies for the delay on this. Note, EVM shows setting a DC common mode voltage of VDDA2*(825/(825+200)) = 2.0V.

    In general, your application looks good.

    Criteria we reviewed:

    • D_VPPOUT (800mV) meets 200mV input requirement (good).  Note that the method of specifying differential voltage is likely different between FPGA and TLK2501 for this specification.  I'm assuming FPGA uses V_pp(V_TXP - V_TXN), while the TLK2501 uses |V_RXP - V_RXN|.  Using FPGA specification method, the VID specification is actually 400mVppd.
    • FPGA can be AC coupled to TLK2501, so common mode voltage on FPGA is not a concern.
    • One thing I wanted to highlight is the maximum receiver common mode specification.  This is specified such that the voltage on the receiver pins does not exceed VDD.  Looking at D_VPPOUT, this is also not an issue for a 2.0V V_CMR.

    Thanks,

    Drew