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THVD1550: How to understand and verify the anti-common-mode interference capability of THVD1550 chip？

Jojo Wang
Prodigy 150 points
Part Number: THVD1550


Hello,

When a communication failure occurs, I am confused and helpless because I don't understand the specific meaning of the specifications.

There is a sentence in the THVD1550 datasheet: Extended Operational Common-mode: ± 15 V

1)、How should I further understand and experimentally verify it?

2)、Is this parameter the anti-common-mode interference capability of the chip?How does the chip's ability to resist common-mode interference?

3)、Is it the circuit that verifies this parameter?Why connect 375 ohm resistors in series instead of adding 15V common-mode interference directly on the bus?

  • 0
    TI__Mastermind 25705 points

    Hi,

    There is a very good video on youtube can take a look.

    https://www.youtube.com/watch?v=h0OoiB1kEx8

    You can verify the spec by doing tests like the diagram you attached. RS-485 works with long distance communication, therefore the ground potential on transmitter end and receiver end could be different. 375Ohm represents the input resistance of the receiver nodes. Assume the transmitter has ground 0V, while the receivers have their own grounding (Vtest). The datasheet says THVD1550 works both way (transmitting and receiving) with Vtest varying from -15V to 15V. Please let me know if anything still doesn't make sense to you.

    Regards,
    Hao