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SN55LVDS32: External Weak Pull-Ups

Scott Foley
Prodigy 10 points
Part Number: SN55LVDS32

Tool/software:

Hello,

I'm working with SN55LVDS32 in a bus configuration in which I need to measure the bus itself. It's difficult to find a buffer that meets reliability qualifications, has enough bandwidth, and has a low enough bias current to sense the bus such that when disconnected the open-circuit fail safe is still functional. I've seen the app-note on terminations, but did not see anything about adding external pull-ups to 'strengthen' the overall pull-ups provided within.

Would adding an external pair of 300 kOhm resistors as pull ups to VCC have negative effects on bandwidth or other parameters?

Thank you,

Scott Foley

  • 0
    TI__Expert 3170 points

    Hi Scott,

    I want to make sure I am understanding correctly. Are you saying that when you try to measure floating receiver inputs that your measurement equipment is loading the inputs and causing the failsafe circuitry to not produce a high output? I wouldn't expect this to happen.

    I wouldn't expect that increasing the pullup strength slightly like you are suggesting will impact performance very much. The biggest concern would likely be any additional stubs created by connecting these external resistors.

    Regards,

    Jack