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SN65HVD888: SN65HVD888

Part Number: SN65HVD888

Hi Team,

My customer is using SN65HVD888 for one of the project and request help for calculating Failsafe Bias resistor values for the RS485 network. 

The device datasheet tabulates various values of the Failsafe resistances and the termination resistance as below,  would like to know the formula for calculating these values.

Can you please help on this.Thanks in advance for the help and support. 

Reagrds, Shinu Mathew

  • Hi Shinu,

    The failsafe resistors work with the bus resistance between A and B to create a three-resistance divider circuit.  The formula for calculating the voltage across the bus is then:

    VID = VCC * [(Bus resistance) / (Bus resistance + pullup resistance + pulldown resistance)].

    For more information on failsafe biasing, you may want to reference this blog:

    Please let us know if you have any further questions.

    Regards,
    Max