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SN74AXC8T245: pin compatible version up to 5V?

Benjamin Brammer
Intellectual 460 points
Part Number: SN74AXC8T245
Other Parts Discussed in Thread: SN74LVC8T245, , SN74LVC2T45, SN74LVC16T245, LSF0108-Q1, TXB0108, LSF0108, SN74LV4T125, CD40109B

Hey Guys,

I made a terrible mistake: I use the SN74AXC8T245PW in my design and reconfigured the VccB to operate at 5V whcih is outside the spec , simply because I forgot that it only supports up to 3,6V . Does there exist a pin compatible version up to 5V? 

best regards

Benjamin

  • 0
    Prodigy 110 points
    Have you looked at the LVC translators?
  • 0
    TI__Guru* 96591 points
    Hi Benjamin,
    The SN74LVC8T245 (PW) is pin-to-pin compatible with the SN74AXC8T245 (PW). It can support 1.8V to 5V translation, however if you operating below 1.8V you will need a 2 stage design (AXC + LVC).
  • 0 in reply to Rigor
    Intellectual 460 points

    No I haven't but thanks for the hint!

  • 0 in reply to Emrys Maier
    Intellectual 460 points
    Hey Emrys,
    thanks for your answer. Perfect! No, I will not have a lower Voltage than 3,3V.

    best regards

    Benjamin
  • 0 in reply to Emrys Maier
    Intellectual 460 points
    I looked more deeper into the datasheet, and sadly your soltuion does not fit my requirements. Since this chip does not have two different DIR pins to set the funtion of bit1-4 and bit 5-8 independently. And exactly that is what I use. But I will look maybe there exists a versin that can do this.

    best regards
  • 0 in reply to Benjamin Brammer
    TI__Guru 56050 points
    Hi Benjamin,

    We do not have dual direction pins on LVC devices. You could consider using SN74LVC16T245 which have them or could consider using SN74LVC2T45 *4.
    The AXC8T245 included dual direction feature but still retains the P2P compatibility with the AVC/LVC devices.
    what is the application using the dual direction, SPI?
  • 0 in reply to ShreyasRao
    Intellectual 460 points

    Hey shreyas,

    thanks for your answer. I use it for SPI and then GPIO input. The Board is a universal digital board for current and future products of the company I work for. with my post I wanted to find a solution without having to adjust my board layout. But all suggestions here don't work without them. So I have only two possibilities: 1. switch back to 3,3V on the secondary side or 2. modify the board layout. 

    Anyway thanks for the suggested solutions :)

    best regards

    Benjamin

  • 0 in reply to ShreyasRao
    Intellectual 460 points

    Hey Shreyas,

    I have searched a bit for a possible revision alternative chip and found the LSF0108-Q1 which makes the DIR pins unnecessary. Please find attached the function of the SN74AXC8T245PW in our current application (with the to high voltage on the B-side). As you can see I am using 4 bits as inputs and 4 as outputs. Off course I loose the buffering with that new LSF0108-Q1 but would you recommend this as a good alternative?

    best regards

    Benjamin

  • 0 in reply to Benjamin Brammer
    TI__Guru 56050 points
    Benjamin,

    I had not suggested the LSF due to this belonging to a different family of translation(auto bidirectional). As you rightly pointed out, the LSF is passive and doesnt provide any buffering like the SN74AXC8T245/LVC8t245 device.
    This relies on external pullup resistors adding to board space and cost.
    You could consider using the TXB0108 device as an alternative which also belongs to the auto-bidi family and provides weak 20uA drive strength enough to interface with Hi-Z loads. This wouldnt require external pullup resistors like the LSF0108. The TXB0108 is suitable for SPI interface you are doing here.
    Let me know what you think about this.
  • 0 in reply to ShreyasRao
    Intellectual 460 points

    Hey Shreyas,
    thanks for your answer. Since this digital board is a universal board also for future products, I think I will need the buffering option as I don't know how long the connections to other boards will be, or what do you think? Sadly there is no buffered version suitable for +5V on the B-side with 4-bits, I think.

    best regards

    Benjamin

    P.S. The CD40109B or the SN74LV4T125 could be an option, right?

  • 0 in reply to Benjamin Brammer
    TI__Guru 56050 points

    Hi Benjamin,

    There is no pin compatible option with SN74AXC8T245 which can support dual direction translation.

    The SN74LV4T125 would be unidirectional and is an option to consider as buffered translator. You would require 2 of these in the system.

    I would not recommend using the CD4K family as they 3.3V would be the corner voltage level and these are relatively older family/ technology.