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DS15BA101 - Both Outputs are fix 1V

Martin15
Prodigy 90 points
Other Parts Discussed in Thread: DS15BA101

Hi,

I have a PCB design where an FPGA (Zynq) drive the DS15BA101 directly.

Because of the absolute maximum ratings of the DS15BA101 the FPGA drive IN+ and IN- of the DS15BA101 with 3,3V and GND.

But when I measure the voltages on the Outputs both are at about 1V. There is no difference if I toggle the input or if it's driven with DC voltage.

Have somebody any idea what I can try next to figure out where the problem is?

RVO is 953Ohm

OUT+ and Out- have each a 49,9Ohm Pull-Ups and a 1uF serial capacitor.

Thanks a lot,

Martin

  • 0
    TI__Mastermind 43795 points

    Hi Martin,

    Sorry more questions than answers to better understand the problem.  Based on your explanation, the input voltage amplitude and common mode should cause the output to change state or switch.

    Is the supply voltage still at 3.3V?

    Is the DAP under the BA101 also connected to GND?

    Have you tried more than one part in this board or design?

    If you can upload a picture of the input waveform and schematic it could also be helpful.

    Thanks and Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 90 points

    Hi Lee,

    thanks for your reply.

    Yes, supply voltage is 3.3V and the DAP is connected to GND.

    I have to populate two DS15BA101 on the board. Both have the same behavior.

    Schema:

    Sorry, but I can't upload an picture of the waveform. Because the oscilloscope is currently out of house (calibration)

    Therefore I tested it with multimeter

    • DC:
      • IN+: 1V (because the Zynq can't drive the 100Ohm, with 3.3V)
      • IN-: GND
      • Out+: +1V
      • Out-: +1V
    • 0.2Hz
      • IN+: +1V/GND
      • IN-: GND/+1V
      • Out+: +1V
      • Out-: +1V
    • 200MHz
      • IN+: +1V (the multimeter can't measure that frequency)
      • IN-: +1V
      • Out+:+1V
      • Out-:+1V

    Hope you can see where the problem is, in the meantime a will populate a new PCB...


    Thanks,

    Martin

  • 0 in reply to Martin15
    TI__Mastermind 43795 points

    Hi Martin,

    I would check your connections to R107 and R120.  The output common mode should be in the 2.8 - 3.0V range.

    Make sure the outputs are terminated near the receiver with 100 ohm differential or 50 ohms each to GND or VDD.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 90 points

    Hi Lee,


    thanks for your answer. Now I got my second populated PCB, with that one I can transmit and receive a 200MHz clock :-)

    So it seems that there is an PCB error on the first board. I will have a further look to that soon.

    But I have another question. When I disconnect the transmitter from the receiver, the receiver set the LOS signal correctly. Have you further information about how that works or when the LOS is set? I ask this question because... is it possible to detect a unpowered but connected board with the help of the LOS signal?

    Thanks and have a nice week,

    Martin

  • 0 in reply to Martin15
    TI__Mastermind 43795 points

    Hi Martin,

    Yes an unpowered but connected board would still produce a "LOS" event on the receiver.  The receiver is looking for the presence of a valid signal on the inputs.  If no signal is present LOS will be output by the receiver.

    Regards,

    Lee