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Choose the right driver

Enzo Bruno
Prodigy 20 points
Other Parts Discussed in Thread: SN74LVC8T245, SN74LVCC3245A, SN74AHCT244, SN74LVC16T245, SN74AHCT16245

For a new project of a 3.3v card inserted in the existing 5v system I have to choose drivers for the bus. The bus is passive of about 25cm in length. At the moment for the existing 5v cards, 74hct245 for bidirectional data bus and 74hct244 for unidirectional control line are used.
Which drivers are recommended as interface between new board at 3.3v and 5v system ?
I have see the 74lvcc3245 and 74lvc8t245 is the right choice ? The relative 244 do not exist ?
The driver can be 8 or 16 bits wide
Best regards
Enzo Bruno

  • 0
    TI__Guru 56740 points
    Enzo Bruno ,

    Welcome to e2e !
    The '245 is direction controlled but many of the applications use it as unidirectional device by tying the DIR pin either low or high. either sn74LVCC3245a or the sn74lvc8t245 would work in this regard.
    You could also consider using the sn74AHCT244 device which can work as 3.3V to 5V translation device.
  • 0 in reply to ShreyasRao
    TI__Guru 56740 points
    For 16 bit options , there are sn74LVC16T245 or the SN74AHCT16245 options as well.
  • 0 in reply to ShreyasRao
    Prodigy 20 points

    Hi ShreyasRao


    Thank for your replay

    I add some clarifications to my question. The system consists of a passive bus on which cards are inserted, from a minimum of 3 to maximum of 14, one is the master and all the others are slave.  All the system is powered to 5v. The new board (of type slave) powered at 5v, will work internally at 3.3v with its regulator. The access time for read/write is about 500ns. Drivers will then have to read and drive the bus from and to the other cards that use the 74hct245 / 74hct640 and 74hct244 / 74hct541, respecting fanout and level rules. The data bus will be bidirectional 5v/3.3v. The address/control line are input line from 5v to 3.3v. The lines to replay at master are output line from 3.3v to 5v. The question is, are the components mentioned the best choice?

    Best regads

    Enzo Bruno

  • 0 in reply to Enzo Bruno
    TI__Guru 56740 points
    Enzo ,

    The components mentioned above will be suitable for your application. with some unidirectional and some bidirectional , you may have to use multiple devices of LVC8T245.