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AM26LV32：About connection of interface ICs of different voltage

kazuo Shiono
Prodigy 20 points
Part Number: AM26LV32
Other Parts Discussed in Thread: SN65HVD78

The supply and reception buffer for RS422 differential signal, the power supply voltage is on the transmission side (5V) and the reception side (3.3V)
Does it work without problems with the circuit configuration?
Also, if there are points to be taken care of by termination resistance etc., please teach me.

  • 0
    TI__Mastermind 25705 points

    Kazuo,

    The answer is yes. You can refer to this post for the detailed discussion. Talking about termination, it's always recommended to put termination resistors at both ends of the transmission. Please let me know if you still have questions.

    Regards,

    Hao

  • 0 in reply to Hao L
    TI__Mastermind 25705 points

    Kazou,

    The hyerplink beats me again. Please use the link below for the discussion.

    e2e.ti.com/.../93260

    I also attach the app note for your reference. Please let me know if you have more questions.


    8883.3V MCU to 5V XCVR Interface.pdf

  • 0 in reply to Hao L
    Prodigy 20 points
    e2e.ti.com/.../93260
          In the standard, 485 is 1: N and 422 is 1: 1
          At Rx (3.3Vp-p) at Tx (5Vp-p), is the amplitude on the Rx side about 4Vp-p from the drive current on the Tx side?
          How does data reception at 3.3V Rx work at this time? (Is it 3.3V with a protective diode etc.)
         
          e2e.ti.com/.../8883.3V-MCU-to-5V-XCVR-Interface.pdf
          The material is connected to a level shifter, or a resistive divider, a zener diode.
          Is it not possible to connect directly as it is?
         
          What I would like to know is whether the RS-422 receiver can replace the 5V specification product with the 3.3V specification product.
         
          Thank you.
  • 0 in reply to kazuo Shiono
    TI__Mastermind 25705 points

    Kazou,

    It's always recommended to put termination resistors on the bus to match the cable impedance. If you do so, the voltage swing on the bus won't be close to rail to rail. On the other hand, even there were no resistors on the bus, 4Vp-p would not be a problem for the RS-485 receiver either, which works with -7V to 12V input voltage range.

    In the app note, one of the reasons of having extra components is to prevent the 3V part from seeing a 5V logic. If your 3V part IO works with 5V TTL (such as SN65HVD78), it should be fine without extra protection.

    Please let me know if you have more questions.

    Regards,

    Hao