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SN65LBC174: harness requirement

Jayaraj Prabakaran
Prodigy 10 points
Part Number: SN65LBC174

Tool/software:

I have a design using SN65LBC174AMDWREP switching max around 10Khz. I like to understand the cable requirements to connect the chip to external circuit. Does the wire have be twisted pair for the low frequency application?

  • 0
    Guru 281760 points

    Using twisted pairs reduces the noise sensitivity. Whether this is important depends on the environment where it will be used.

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    can you direct me any of the EMI harness requirement to help establish the twisted pair requirement.

  • +1 in reply to Jayaraj Prabakaran
    TI__Guru 59680 points

    Jayaraj,

    The main thing you want to look for in a differential cable is impedance matching with your system. Generally with RS485 we see customers use 120 ohm termination so the cables are normally have 120 ohm characteristic impedance. For RS422 it's normally a single 100 ohm resistor termination so you would use a 100 ohm characteristic impedance cable. 

    We don't normally give suggestions/recommendations on the specific cable since we don't sell cables but for lab testing we use Belden 3105A. We typically look for 22 gauge cable (you can use thicker if you want but it's not necessary). If you expect a lot of external noise, you can look at using shielding. (This is useful to reducing noise emitted and preventing noise to couple onto the signal.). Twisted pairs are generally expected to maximize the effect of using differential signaling (emitted noise gets reduced and also coupled common mode noise is lower).

    -Bobby