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SN74LVC1T45: Problem with DIR, Vcca and Vccb

Carlos Lopez1
Prodigy 30 points
Part Number: SN74LVC1T45
Other Parts Discussed in Thread: SN74LVC1G17

Hello,

I am using a SN74LVC1T45 for repeater purposes, after some wire, for a logic 5VDC signal. I am supplying with 5VDC Vcca,Vccb; and also DIR pin. The 5vdc supply signal is the same for all three pins. It could be any issue because of that, in the power sequence or in the turn off? I have read in the data sheet that pin DIR must be supplied with Vcca, but is it bad if it is shared with Vccb?

Thank you in advance for your response.

Regards,

Carlos López Cernuda 

  • 0
    TI__Genius 16735 points

    Hi Carlos,

    There is no issue in using the same supply for the VCCA, VCCB and DIR pins. If VCCA and VCCB are at different supply voltages then the Voltage High level of the direction pin should be the same as VCCB value. Since for you both VCCA and VCCB are at 5V then its okay for direction pin use VCCA supply to get to 5V.

    You can also use other buffers that don't have direction pins, since you are not level shifting the signals or changing their directions.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    Prodigy 30 points

    Hi Karan,

    Thank you so much for your answer. We are having some problems in a circuit board, and we saw that this IC was broke, we thought it could be because of that.

    Which others buffers would you recommend?

    Carlos

  • 0 in reply to Carlos Lopez1
    Guru 317390 points

    If the input signal comes through a long wire, it might not comply with the rise/fall time requirements of the SN74LVC1T45. So it might be a better idea to use a buffer with a Schmitt-trigger input, i.e., SN74LVC1G17.