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DS90UB927Q-Q1: Why does DS90UB927Q not support coax and DS90UB947 does?

Martijn de Milliano
Prodigy 190 points
Part Number: DS90UB927Q-Q1

On http://www.ti.com/interface/fpd-link-serdes/display-serdes/overview.html there is a table showing various devices with resolution and interface. Why is the parameter "Coax" not set for DS90UB927Q, does this mean we cannot transport the FPD-Link using 50Ω coax with this particular chip?

I understood from the training at https://training.ti.com/fpd-link-learning-center that for all FPD-Link III we can either use a 100Ω differential line using HSD connectors or 50Ω coaxial single-ended line with extra 50Ω termination resistor and FAKRA connectors?

I saw in a different post something about coax working but only STP officially supported, but why can you claim support for the one device and not the other if they are using the very same electrical interface (FPD-Link III)? Any experiences with using DS90UB927Q with coax?

  • 0
    TI__Mastermind 37500 points

    Hello Martijn,

    The DS90UB927-Q1 does not list Power over Cable, in the datasheet.  The EVM does uses the STP data output.  However the device is capable of Power over Coax.   As you indicated the 50 ohm power over cable , while the STP is 100 ohm differential.   The EVM does not support this, you could modify the EVM to test it.  

    In your use case, you can follow the  one of the two attached Power Over Cable appnotes for DS90UB913A, or DS90UB953.

    for the DS90UB953, has the schematic section for the Power over Cable POC.

    power_over_coax_ds90ub913a_snla224.pdf

    Regards,

    Joe Quintal

  • 0
    TI__Intellectual 2930 points

    DS90UB947 was designed  to support both Co-ax cable and STP cable while UB927 was built to support only STP cables.

    For co-ax support please use DS90UB921 (it has RGB interface) . 

    UB925 and UB927 are our first generation FPD-Link III devices and they do not support Co-ax as at the time of their release, the only cable use cases in automotive applications are STP based. 94x(949,947 etc), 95x(953, 954 etc), 921 are latter generation FPD3 devices that support both co-ax and STP cables

    Regards

    Vijay

  • 0 in reply to Vijaya Ceekala
    Prodigy 190 points

    Thanks for your answer. The interface of my display is LVDS, so therefore I suggested the DS90UB927Q instead of DS90UB921.

    Power over coax is not a requirement, but there are more options to connect 50 ohm single-ended coax cable than 100 ohm differential. What is the reason that automotive prefers STP?

    For connectors, is it required to use something like Rosenberger 476-D4S20L-40MA5-Z, or is it also possible to two pins on e.g. Molex 36638-0006 and then twist the wires in a shielded cable? How necessary is it to use a shielded cable, could it also be unshielded like CAN?

  • 0 in reply to Martijn de Milliano
    TI__Mastermind 37500 points
    Hello,
    The high speed serial signals are tested with the specific STP connectors and cable. The performance is tested in this environment, and this is the recommended application. There is an application note that discusses, STP and Coax for FPDLink application, www.ti.com/.../slyt726.pdf
    Regards,
    Joe Quintal