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AM26LV31: Example circuit for Quad line driver and receiver

SARAVANAN S
Prodigy 10 points
Part Number: AM26LV31
Other Parts Discussed in Thread: AM26LV32,

Tool/software:

Hello,

Greetings !!!

Can you provide some reference circuit for AM26LV31 (driver) and AM26LV32 (receiver)?

There are some reference that I have taken from internet, where I could see 120ohm resistance is added in between input(+) and input(-) of receiver, and also pull up of 2K ohm is connected between input(+) and Vcc and pull down of 2K ohm is connected between input(-) and Gnd. Is it mandatory? if yes, what should be done with the driver input line?

Thanks in advance,

Saravanan

  • 0
    Guru 311370 points

    The 120 Ω resistor is the termination. For RS-422, it is typically 100 Ω, but it should match the characteristic impedance of the cable. It is almost always needed, except for very low speeds.

    The other resistors are fail-safe biasing resistors; they are needed if the sender can be powered down or disconnected.

    See the RS-422 and RS-485 Standards Overview and System Configurations application report.

  • 0
    TI__Guru 67530 points

    Hi Saravanan,

    Clemens is correct as usual.

    Figure 19 in the document that he references is how you would set up a very basic RS422 bus. The 100 ohm termination resistor would sit on the furthest receiver node relative to the sending node. 

    You can place external fail safe resistors on one of the receiver nodes to add noise immunity when the system is idle or the driver is disconnected/unpowered. It's not required but can help. I would recommend adding them as do not populate resistors if you don't need them since they are nice to have when you do need them.

    -Bobby