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THVD1452: Schematic review - THVD1452DGSR

Vignesh P
Prodigy 40 points

Part Number: THVD1452

Hi,

Attached file is schematic of THVD1452.

Please help to review the schmatic for RS485 full-duplex transceiver THVD1452.image.png

  • 0
    TI__Mastermind 25172 points

    Hi Vignesh,

    You do not need to add the pullup and pulldown resistors on the RS-485 bus pins. The THVD1452 has them internally. 

    I would recommend a pulldown resistor on the DE pin, not a pullup. During power on/off of your system, you don't want accidental transmissions to the bus. 

    Best,

    Ethan

  • 0 in reply to Ethan Sempsrott
    Prodigy 40 points

    Hi Ethan,

    Thanks for the reply. As we plan to use the part "SN65HVD73DGS / SN65HVD76DGS" as an alternate, can we use the same configuration (without pullup and pulldown resistors on the RS-485 bus pins) for the alternate as well? 

    We added 120E termination resistors for both transmission and receiver side. Is this fine?

  • 0 in reply to Vignesh P
    TI__Mastermind 25172 points

    Hi Vignesh,

    Those transceivers also have internal biasing. So they don't need the external pullup/pulldowns. However, if you intend to use other transceivers without these resistors, then you can just keep them populated.

    Yes, 2 points of termination are necessary such that the overall bus impedance is 60 Ohms (120+120 in parallel). Your configuration is correct.

    Best,

    Ethan