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TMDS251 source side application

Mirko Pfitzner
Prodigy 40 points
Other Parts Discussed in Thread: TMDS251, TMDS261B

Hello TI Support Team!

Can I use the TMDS251 device also for source side applications?

So e.g. can we drive a DVI monitor via a DVI cable (normal length) at the TMDS output?

Thank you very much for the answer in advance.

Best regards,

Mirko

  • 0
    TI__Expert 6745 points

    TMDS251 has been used as DVI source or you could also use the TMDS261.

  • 0 in reply to Ken Shaw
    Prodigy 40 points

    Thanks Ken.

    Data sheet of TMDS261B says: "TMDS261B device is not
    intended for source side applications such as external switch boxes"

    (In data sheet of TMDS251 it is not mentioned)

    So my question is why exactly? And what does it mean exactly "is not intended for".

    Maybe only because of the ESD protection at the output, which you can't switch off.

    We have here an application which works with a DVI monitor. But we get DC voltage back from monitor on the board, when it is switched of via the TMDS lines via the ESD diodes.

    I that the reason for the recommondation?

    Best regards,

    Mirko

  • 0 in reply to Mirko Pfitzner
    TI__Expert 6745 points

    If the two TMDS sources are fixed and known and you just need to switch them to a single output, I would recommend the 361.   The note for source application is really more for something like a KVM switch where you can have varying input sources and cable lengths to a single output.

  • 0 in reply to Ken Shaw
    Prodigy 40 points

    We are using (right now in first sample; B-sample to be build) the TMDS251 to switch between a TMDS input coming from PCB (another chip) and a TMDS input coming from a normal length DVI cable via DVI connector. The output goes directly to a DVI connector which feeds a DVI monitor (also normal length). This application do work right now.

    For some reasons (risk etc......) we would like to keep that device in next sample. (But we have to disconnect the chip at unpowered state from the supply rail, because monitor feeds DC voltage back via ESD protection diodes.)

    My question is: Do you see any reasons not to do so? Or do you think this special use case is OK?

    Mirko

  • 0 in reply to Mirko Pfitzner
    TI__Expert 6745 points

    You have seleceted the proper solution to the problem.

  • 0 in reply to Ken Shaw
    Prodigy 40 points

    Hello Ken,

    still 2 questions. We tested a TMDS261B device (since pin compatible) instead of the TMDS251 in our system and do not get the leakage path to the Vcc rail via the protection diodes which do cause the "repower" problems.

    Q1: So can we use the TMDS261B in our "source side application" with normal cables despite of the statement "TMDS261B device is not
    intended for source side applications such as external switch boxes"?

    Q2: Do you know the exact differences - especially the output stage - between the 2 devices (besides ESD protection)?

    Best regards,

    Mirko

  • 0 in reply to Mirko Pfitzner
    TI__Expert 6745 points

    Please contact me directly at kshaw@ti.com for further information.