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Original question:

THVD1550: Pull up and pull down resistor

THVD1550: Pull up/down resistors on Bus I/O ports

Roy Hsu
Genius 9320 points
Part Number: THVD1550

Hi Team,

This is a follow-up question to this post: https://e2e.ti.com/support/interface/f/138/p/852125/3151814?tisearch=e2e-sitesearch&keymatch=THVD1550#3151814

In this post, Max mentioned that the pull-up/down resistors are optional for failsafe biasing. However, my question is since THVD1550 already has Open, Short, and Idle Bus Failsafe features. Do we still need those optional resistors?

Thanks!

Roy

  • 0
    TI__Guru 62920 points

    Hi Roy,

    The integrated open/short/idle failsafe in THVD1550 works by shifting the receiver "VIT" input threshold slightly negative so that a 0-V differential input is reliably above the "VIT+" (high-level input) threshold and is ensured to be reported as a high.  This means that even without external biasing resistances, the transceiver will still support failsafe functionality (since idle/open/short cases would result in a 0-V input condition).  However, since the function is internal to the receiver circuitry, it does not affect the other nodes on the bus.  If those other nodes do not also have internal failsafe biasing, then they may still need to implement it via external resistances.

    Max