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DS90LV047A: /DS90LV48A: Alternative that supports 2.5V input/output from FPGA

Nicholas Carley
Genius 9335 points
Part Number: DS90LV047A
Other Parts Discussed in Thread: DS90LV048A

Hello,

I'm looking to interface this device (or a similar one) to an FPGA's LVDS ports which operate at 2.5V.

Do we have a similar devices to the DS90LV047A/048A which can interface at 2.5V or is there a way to change their signal level to 2.5V?

Thanks,
Nick

  • 0
    TI__Mastermind 43795 points
    In Nick,

    The DS90LV047A / 048A LVDS port is directly compatible to a FPGA 2.5V LVDS port.

    On the 3.3V LVCMOS side I would recommend using an open-drain or voltage translation buffer to change from 3.3V to 2.5V if necessary.

    Regards,
    Lee
  • 0 in reply to Lee Sledjeski
    TI__Genius 9335 points
    Hi Lee,

    Sorry let me clarify the application better.

    There are two signal chains.
    1. (LVCMOS/LVTTL) --> DS90LV047A (To LVDS) --> FPGA LVDS 2.5V input ports
    2. FGPA 2.5V LVDS output ports --> DS90LV048A --> (to LVCMOS/LVTTL)

    The output voltage of the DS90LV047A is 3.3V (LVDS) which goes into the FPGA directly. The FPGA is rated for 2.5V.

    I am looking for a device similar to DS90LV047A which has 2.5V output for LVDS. You mentioned a voltage translator as an option, do you have a suggested device for this application?

    Reviewing the DS90LV048A datasheet, its LVDS inputs (VIH and VIL) should accept 2.5V LVDS from the FPGA, can you confirm this?

    Thanks,
    Nick
  • 0
    TI__Genius 9335 points
    Hi Yaser,

    Thank you.

    If LVDS is 1.2V +/- 350mV, why is the VIH and VIL of the DS90LV048A 2V and 0.8V respectively? (Page 5 of the datasheet)

    Nick
  • 0 in reply to Nicholas Carley
    TI__Genius 10250 points
    Hello Nicholas,

    If the FPGA has LVDS ports then DS90LV047A/048A can interface to those LVDS ports, even if the FPGA is powered from 2.5V (or other voltage, for that matter). The signalling on the LVDS ports is standard (differential voltage is ~ +/- 350mV, and the common mode is ~1.2V) and should not depend on the supply voltage.

    Regards,
    Yaser
  • 0 in reply to Yaser Ibrahim
    TI__Genius 10250 points
    Hello Nicholas,

    Sorry for the confusion. The VIH and VIL should be for the single-ended (LVCMOS/LVTTL) side, not the LVDS side. LV048A datasheet should probably have only VOH/VOL!

    At any rate, the LVDS side is standard and should work with other LVDS signalling independent of the supply voltage.

    Regards,
    Yaser
  • 0 in reply to Yaser Ibrahim
    TI__Genius 10250 points
    Actually, I just remembered the LV048 has 2 logic inputs which are EN and /EN. VIH/VIL applies to those inputs, and that should be clarified in the datasheet

    Regards,
    Yaser