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THVD1552: Compatibility of THVD1552 and SN65HVD1476

JC Montavon
Prodigy 20 points
Part Number: THVD1552
Other Parts Discussed in Thread: SN65HVD1476, THVD1452

I'd like to implement a full duplex RS-482 bus. I'm thinking about using THVD1552 for the master and SN65HVD1476 for all slaves. I cannot use SN65HVD1476 for the master because there's only 5V available for power supply and the boards with slave transceiver already include SN65HVD1476. Will this configuration work fine?

I have seen that I could use THVD1452 both both master and slaves. Because I have selected VSSOP package, THVD1452DGS are not yet available. So this is only a future solution.

Thanks for your help

  • 0
    TI__Intellectual 2090 points
    Hello JC,

    You should be able to mix the 5V THVD1552 device with the 3.3V SN65HVD1476 devices. The only issue you may see is if you implement fail-safe resistors externally in your network to bias the receiver voltages during an idle bus. If one set of fail-safe resistors is biased using the 3.3V rail and another set is biased using the 5V rail, then you will see a current path between the resistors that you may want to block with a diode.

    However, both the THVD1552 and the SN65HVD1476 devices possess features that ensure a known state of the receiver during an idle bus state. This is accomplished through the receiver threshold parameters and integrated hysteresis. This means that you should have no need to implement an external resistor-based solution for the idle bus state. Therefore, the current path issue from above is a moot point. You should be able to proceed with the solution that you proposed.

    Best Regards,
    Max Megee
    TI Transceiver Applications
  • 0 in reply to Max Megee
    Prodigy 20 points

    Thank  you very much. What do you mean exactly by "if you implement fail-safe resistors externally in your network to bias the receiver voltages during an idle bus"?

    Best regards,

    JC

  • 0 in reply to JC Montavon
    TI__Intellectual 2090 points

    Hi JC,

    Apologies for the delay in response for your question.  You can refer to this blog post for more detail about external resistor schemes for idle-bus biasing networks in RS-485:

    https://e2e.ti.com/blogs_/b/industrial_strength/archive/2016/12/06/rs-485-basics-two-ways-to-fail-safe-bias-your-network

    However, I don't think that you will need to implement any of these strategies, since the transceivers in your use-case should take care of this!

    Thanks,

    Max Megee