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SN75LBC180: Communication with products with different power supply voltages

Part Number: SN75LBC180
Other Parts Discussed in Thread: SN65HVD1473, THVD1450


Is there any problem in connecting 3.3V drive product (SN65HVD1473) and 5V drive product (SN75LBC180D) for communication?

Please tell me about points to note.

Best regards,


  • Hello,

    Both 3.3-V and 5-V powered RS-485 transceivers will meet the signaling requirements of the TIA/EIA-485 physical layer, and so they can communicate with one another without issue.  The only thing I can think of to be cautious of is use of external failsafe biasing resistances (i.e., to set idle-state differential biases on the bus).  These would ideally only be installed on one node only.  If there were a pull-up resistance to 5 V on one node and a pull-up to 3.3 V on an other node, current could flow from the higher voltage node to the lower voltage supply.  If this is a concern for the application, a diode can be placed in series with the pull-up resistance in order to block reverse current flow into the 3.3-V rail.

    By the way, we do have some newer RS-485 transceivers such as THVD1450 that you may want to consider for new applications. 

    Please let me know if this is not clear or if you have further questions.