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SN65HVD1781: 5V VCC 3.3V IO

Mark Ackerson
Genius 10190 points

Part Number: SN65HVD1781

Customer asked me to confirm SN65HVD1781 operating from a 5V supply is able to communicate directly with a 3.3V MCU.

SN65HVD1781 data sheet specifies Vih min = 2V and typical 3.3V MCU Voh min would be 2/3xVCC or 2.2V.  So no concerns there.

The only caveat I see is with 5V VCC, the output level of R could violate abs max of the MCU input.  Unless the IO is 5V tolerant.

Let me know if you would agree.

Regards,
Mark

  

  • 0
    TI__Guru 53535 points

    Hi Mark,

    You analysis here is right. The input pins should have no issue recognizing the input-high from the 3.3V MCU pin. The concern with this configuration is that the R pin will use the 5V Vcc as a reference for its high-level output, which could potentially be a problem if the MCU cannot tolerate this voltage. If this is the case, a FET may be used as a voltage translator for this signal to safely convert it to something the MCU can tolerate. 

    Let me know if you have any more questions.

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Genius 10190 points

    Thanks for confirming Eric!

    Regards,
    Mark