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SN65HVD55: SN65HVD55 FAIL SAFE FEATURE

Shreenidhi Patil
Expert 3186 points
Part Number: SN65HVD55

hello team

 

For SN65HVD55 RS485 transceiver, Fail safe feature given for open, short and idle bus (as per datasheet). So as per my understanding, we do not  need external bias resistors in the bus lines, only termination resistors needed as per the characteristics of the cable.

Please let me know if my understanding is right

 

Besides if you have any typical schematic it shall be of great help

 

 

thank you 

  • 0
    TI__Guru 62910 points
    Hi Shreenidhi,

    Yes, that is correct. The SN65HVD55 has receiver input thresholds that are skewed in the negative direction so that differential inputs close to 0 V are interpreted as logic high levels. This means that the receiver output will be high (rather than toggling or indeterminate) when a fault condition resulting in a 0-V differential signal occurs. External biasing resistors can still be used if desired (e.g., if other receivers on the bus need them or if noise margin needs to be improved), but they are not necessary. You are right that termination resistors should still be used (typically 120 Ohms between A and B connected at the two distal ends of the cabling).

    Best regards,
    Max