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AM26LV31: About differential voltage

Part Number: AM26LV31
Other Parts Discussed in Thread: AM26LV32,
PCB1 in the figure is a board developed in the past.
PCB1 circuit cannot be changed.
I am currently developing PCB2.
I want to use AM26LV31 and AM26LV32.
Is there any problem with the circuit in the diagram?

I am particularly worried about:
There is a fail-safe circuit on the A1 and B1 lines of PCB1, can the AM26LV31 output the required differential voltage (200mV) between A1 and B1?
The cable is 11in.
  • Hi,

    The AM26LV31 should be able to drive the required differential voltage through the fail safe circuitry in typical conditions. It may introduce some problems if a particularly lossy cable is used.

    In PCB2, the unused AM26LV32 inputs can be left disconnected. Internal fail-safe circuitry can draw unneeded power if tied to external voltages.

    Let me know if you have any other questions.

    Regards,

    Eric

  • Hi,

    I have two questions.

    >In PCB2, the unused AM26LV32 inputs can be left disconnected. Internal fail-safe circuitry can draw unneeded power if tied to external voltages.

    Does it mean that IC4's 4A and 4B should be open (not connected)?
    What is the specific differential voltage generated between 1A-1B and 2A-2B of IC1?
    Regards,

  • Hi,


    1. Yes. 4A and 4B on IC4 may be left disconnected to save power.

    2. Assuming an ideal wire, I simulated the following theoretical Vdiffs for 1A-1B.

    Vh:   Vdiff =  1.61v   Iy = -20.15mA   Iz =  19.95mA
    Vl:   Vdiff = -1.32v   Iy =  19.98mA   Iz = -20.19mA
    Open: Vdiff =  144.3mV

    Note that when the driver is disabled(high impedance), the fail-safe circuit it not able to pull the line differential above the threshold of 200mV. However, the reciever's failsafe condition defaults to the HIGH when the line is in a high impedance state (see section 8.4.1).

    Vdiff for 2A-2B should be near the typical value of +-1.5v listed on the datasheet with 100ohm termination.


    I hope this helps. Let me know if you have any more questions.


    Regards,
    Eric