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SN74AXC8T245: SN74AXC8T245 usage clarification

Kethan P
Prodigy 30 points

Part Number: SN74AXC8T245

Dear Texas Instruments Team,

I am planning to use SN74AXC8T245 in my design for voltage level translation.

My setup:

  • VCCA = 3.3 V (since OE and DIR Referenced to 3.3V)
  • VCCB = 1.2 V
  • I want to use it for SPI signals and normal GPIO.

My plan:

  • Use 4 channels for up translation (1.2 V to 3.3 V)
  • Use 4 channels for down translation (3.3 V to 1.2 V)

I have few doubts:

  1. In TI Website, RGMII is mentioned as an application for this IC. Can I use this IC for SPI and GPIO as well? 
  2. Datasheet says simultaneous up and down translation works only when both VCCA and VCCB are at least 1.4 V.
    But in my case VCCB is 1.2 V.
    So can I still use 4 channels for up and 4 for down at same time?
  3. If above is not recommended, what issue will happen?
  4. Any better device suggestion for this use case?

Please clarify.

Thank you for your Support.

 

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  • 0
    TI__Mastermind 41850 points

    Hello Kethan,

    See my answers below:

    1. Yes, this part can be used for both SPI and GPIO signals

    2, 3. I'm trying to find more information about the "both VCCA and VCCB are at least 1.40V" comment. Since this is listed on the datasheet, I would not recommend this part if you are trying to perform simultaneous up and down translation when VCCB = 1.2V.

    4. I would recommend SN74AVC4T774 for SPI and SN74AVC4T245 for GPIO.

    Regards,

    Josh

  • 0 in reply to Joshua Salinas
    Prodigy 30 points

    Hi joshua,

    Since PCB space is a concern, we intend to use this level translator. Could you be able to get more information about the statement mentioned in the datasheet on a priority basis?

    I have also attached a screenshot of a thread in which some user discussed this earlier on the forum.

    Regards,

    Kethan

  • 0 in reply to Kethan P
    TI__Mastermind 41850 points

    Hello Kethan,

    I'm still waiting for a response from the team. Thank you for your understanding.

    Regards,

    Josh

  • 0 in reply to Kethan P
    TI__Mastermind 41850 points

    Hello Kethan,

    I talked with the team regarding this topic. They mentioned in some extreme process, voltage and temperature corners there is a possibility of the part experiencing output glitches. However, I was informed that this is not likely under normal operating conditions. 

    Given this information, you can use a supply voltage lower than 1.4V without any issues. 

    Regards,

    Josh

  • 0 in reply to Joshua Salinas
    Prodigy 30 points

    Hi Joshua,

    Thank you for the update.

    Could you please let us know what specific extreme conditions you were referring to, so that we can be prepared or implement any necessary measures in our design?

    Regards,

    Kethan

  • 0 in reply to Kethan P
    TI__Mastermind 41850 points

    Hello Kethan,

    The simulation corners I'm referring to are over the operating temperature and supply range. As long as you keep the AXC within the recommended conditions, there shouldn't be any issue.

    Regards,

    Josh