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SN65HVD11: Applied in multi-voltage networks

Walsh
Intellectual 950 points
Part Number: SN65HVD11

Hi,

Does SN65HVD11 which has failsafe function need failsafe bias network in multi-voltage networks?

Could SN65HVD11 work regularly when the voltage on pin A or pin B is 4.4V?

Schematic diagram is as below,

Thanks,

Walsh

  • 0
    TI__Guru 62910 points
    Hi Walsh,

    Yes, it is OK for the voltages at the A and B pins to be anywhere in the range from -7 V to +12 V. This is needed per the RS-485 standard in order for the system to be able to tolerate ground potential shifts from node to node.

    The HVD11's failsafe implementation does not require external biasing resistors, although it is OK to include them as well. This device implements failsafe biasing by shifting the positive-going differential input threshold below 0 V (it is typically set to -65 mV). This means that if a fault condition occurs that results in a 0-V differential input (for example, if the line is undriven, if A and B are shorted together, etc.), the receiver output will be logic high rather than indeterminate.

    Please let me know if you have any other questions.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Intellectual 950 points
    Hi Max,

    Thanks.

    Walsh