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SN65HVD888: Signal Amplitude

Patrick Zeng
Intellectual 1090 points
Part Number: SN65HVD888

Hi team,

  My customer is using SN65HVD888 as slave and SN65HVD3082 as master. Point-point test, cable length is 50CM, VCC = 5V; The AB differential signal for both devices is captured as below: the signal amplitude from 3082 is different from the 888. I'd like to understand the reason why the amplitude is different? And what is the typical parameter the determines the amplitude? Thanks.

Regards,

Patrick

  • 0
    TI__Guru 62910 points

    Hi Patrick,

    For a given transceiver, the output amplitude will generally reduce with higher output loading (lower effective load resistance), increased cable loss (which typically increases with distance), and with decreasing VCC.

    Between two different transceivers operated under the same conditions, differences in output amplitude can be expected based on differences in design.  The most important factors are the effective driver output impedance and the voltage loss associated with the integrated reverse-polarity protection.  You can read more about the different parts of an RS-485 driver circuit and how they can influence performance in this blog:

    https://e2e.ti.com/blogs_/b/industrial_strength/archive/2015/06/16/rs-485-basics-the-rs-485-driver

    Please let us know if you have any further questions.

    Regards,
    Max