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SN65HVD3082E: SN65HVD3082E communication problem

Sunny Qin
Expert 4890 points
Part Number: SN65HVD3082E
Other Parts Discussed in Thread: SN65LBC184

Hi Team,

Here is south China FAE Sunny, we meet a SN65HVD3082E communication problem, customer use SN65HVD3082E communicate with USB 485 debuger, the wire is only 1 meter, the SN65HVD3082E is on a circuit board which powered by isolated AC/DC power module(isolated from the ground of 220V power line), and the USB debuger is connect to PC, and PC`s GND is connect to ground to  of 220V power line.

we found that SN65HVD3082E output lots of noise even USB 485 debuger don`t send any data:

But SN65LBC184 and SP483(local brand 485 device) can work good at this condition, customer are using SP483 currently, we want to use SN65HVD3082E to replace it, but it meet this problem, SN65LBC184 can work, but price is too high.

Could you help to give some comments on why SN65HVD3082E meet this problem while SN65LBC184 not?

Thanks very much.

Regards, Sunny 

  • 0
    TI__Prodigy 200 points
    Hello Sunny,

    It looks like the oscilloscope waveform in your post shows the R output of the SN65HVD3082E, is that correct? Would it be possible to also get oscilloscope waveforms for the bus pins A and B while this is happening? Also would it be possible to get similar waveforms of the A and B pins when the SN65LBC184 device is used and the problem is not present?

    It is hard to say for certain why the receiver output of the SN65HVD3082E is acting differentially than the SN65LBC184 without seeing what is happening on the bus pins. My initial thought is the ground shift between the circuit board and the USB 485 debugger is causing a large common mode voltage or noise to appear on the bus.

    Best Regards,
    Richard Broughton
    Transceiver Interface - Applications Engineer