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SN74LVC8T245 wrong output issue

Chen Bogey8
Mastermind 9990 points
Other Parts Discussed in Thread: SN74LVC8T245

Hi Sir

As enclosed file, our Vccb connect to 5V, and we application SN74LVC8T245 in B to A, and B side is connect to connector.

but when we touch connector with hand, the A side will have outpput. is there have some suggestion for us?1731.level_shift.docx

  • 0
    Guru 74080 points
    Hi Chen!

    This is absolutely normal for high impedance inputs. What you see is the line frequency that is present everywhere. You act as an antenna and when touching the input you feed this signal into the device. Look at the scope signal - the period is slightly over 15ms. I guess you have a 60Hz line (we have 50Hz in Germany) and 60Hz is a period of 16.6ms. You can add pull-up or pull-down resistors to the inputs. 10k for example.

    Dennis
  • 0 in reply to Dennis Eichmann
    Mastermind 9990 points

    Hi Dennis

    thanks for yor reply, and customer curios another thing is from the input single, it is not reach Vih level, why we still can measure the output signal?

    due to board space concern, is there any suggestion to avoide this issue?

                                                                                                Bogey