• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 47 subscribers
  • Views 406 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TX7516: Input termination resistance setting for LVDS SPI mode differential inputs

Stefan Schoenmaker
Prodigy 10 points
Part Number: TX7516


The TX7516 Pulser IC has a programmable input termination resistance on the SCLK, SDATA and SEN input buffers(configured in differential SPI mode).
Table 9-25 lists the four termination setting that are possible.

Which purpose requires the default termination setting of 400Ω? Chapter 7.6 of the datasheet specifies a RSPI_TERM of minimum 90Ω maximum 130Ω.
Is it possible to use the 400Ω input termination setting in a configuration of four differential SCLK input buffers, connected in parallel from four different TX7516 chips.
For the purpose of achieving a point -> multipoint receiver configuration without additional fanout buffers.

  • 0
    TI__Expert 7130 points

    Hi Stefan,

    Thanks for reaching out.

    Your question has been received. Someone from the ultrasound transmit team shall reply to you as soon as possible.

    Thanks & regards,

    Abhishek

  • 0
    TI__Intellectual 1790 points

    Hi Stefan,

    Thanks for reaching out and sorry for the delay in response.

    Yes, you are right. The different termination settings will be useful if you use the same buffer (in FPGA) to drive multiple devices, without the use of additional fanout buffers.

    Thanks and Regards

    Savyan

  • 0 in reply to Savyan Kanisserry
    Prodigy 10 points

    Hi Savyan,
    Thanks for the feedback.
    Do you have more information on how I should connect 4 SCLK LVDS receive buffers to a single driver buffer?
    in the described scenario I have 4x 400Ω termination resistor in parallel, by default at startup, this is not covered by any standard.
    From my experience I would say: connect the differential pairs to the receive buffers with equal branch length. 
    Do you have additional considerations for me to optimize this configuration, regarding additional termination requirements?

    best regards

    Stefan

  • 0 in reply to Stefan Schoenmaker
    TI__Intellectual 1790 points

    Hi Stefan,

    Please refer to the below application note on LVDS signaling. The section on Multipoint/Multidrop LVDS covers the case where multiple receivers are involved. This also contains the design considerations to be followed in this scenario.

    https://www.ti.com/lit/ug/snla187/snla187.pdf?ts=1690775986067&ref_url=https%253A%252F%252Fwww.google.com%252F

    Thanks and Regards

    Savyan

  • 0 in reply to Savyan Kanisserry
    Prodigy 10 points

    Hi Savyan, 
    Excuse my late reply, but I was out of office.
    Thanks for referring to the LVDS signaling documentation, I have read the multidrop/multipoint section and it describes exactly the preferred situation for my application,1 tx device(fpga) and 4 rx devices(tx7516). There is one thing that is still not clear to me, after a TX7516 device reset, the default termination resistance of each SCLK receive buffer is 400Ω. How is this compatible with the Multidrop/Multipoint section that uses only a single termination resistor of 100Ω at the end of the differential pair near the last rx device. Can I connect 4 SCLK buffers in parallel also resulting in 100Ω termination?  

    Best regards.

  • 0 in reply to Stefan Schoenmaker
    TI__Intellectual 1790 points

    Hi Stefan,

    In the above application, if all the receive buffers present the same termination impedances, it can be treated as though they are all connected in parallel with an effective impedance of R/4. Upon reset, we chose the value of 400ohm for R so that even if 4 receive buffers are connected in parallel, it will present ~100ohm and will not cause significant attenuation to the signal. Had we chosen 100ohm as the default value of R, the above situation will see an effective impedance of ~25ohm and the devices may not respond to the SPI write. For your application, after the devices are reset, you can remove the termination resistances of all the buffers, except the last one and modify this value to 100ohm. 

    Thanks and Regards

    Savyan