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Need level translation for - SN74LVC2G66: 3.3V in - to - 5V, 3.3V, 2.5V. 1.8V selectable out.

John Artis
Prodigy 35 points
Other Parts Discussed in Thread: SN74LVC2G66, LSF0102, LSF0108

Hello,

I need help with SN74LVC2G66. There is a circuit on page 1 of scyb016.pdf "Example 2", which is almost exactly what I need, but I am using a micro-controller @ 3.3V and not the 5V shown. I still want the full range of output translated voltages: 5V, 3.3V, 2.5V, 1.8V though. I considered using two such devices, the first one in reverse to go from 3.3V to 5V, then using the circuit as shown, but I wonder if there is a more elegant way to accomplish this using one SN74LVC2G66 ?

Any help would be greatly appreciated!

Thanks...

  • 0
    TI__Mastermind 46480 points

    You should Be able to use one of these LSF0102.  Your lowest voltage should be VrefA and VrefB can be anything that is at least 1V above VrefA. Then the input or aoutputs can be pulled to any level between Vref A and 5.5V

  • 0 in reply to Chris Cockrill
    Prodigy 35 points

    Hi Chris,


    Thanks for the feedback!


    I'm using a micro-controller running at 3.3V, but I still want to be able to select any of the 1.8V/2.5V/3.3V/5V outputs.

    Is it a valid solution to first use one LSF0102 to level shift down to say 1.2V by connecting the output of my microcontroller (3.3V) to the VrefB side and setting VrefB to say 3.3V, then setting the VrefA to say 1.2V to get the output shifted down to 1.2V, then use another LS0102 with VrefA set to 1.2V, and VrefB adjustable to 1.8V/2.5V/3.3V/5V ?

    I hoped there is an easier solution but am willing to do this if it works, but my intentions are to use say a LDO, DAC, and OpAmp to set the voltage to the standard output values on the VrefB side without having to complicate the selection process.

    Also, is there an IC choice which will work for all ports such as I2C, SPI, DIO, CAN ? If not can you please suggest different level translators for each?


    THANK YOU!

  • 0 in reply to John Artis
    TI__Mastermind 46480 points

    Using 1 LSF0108 should work for all you voltage levels.

    Set VrefB to 5V VrefA to 1.2V.    The voltage on all I/O 's will now only go to 1.2V but they can be pulled to any level between 1.2V and 5V.  You can pull any of the I/Os up to different voltages at the same time.

    I have attached an slide show on how voltage clamps work that may help. The LSF part work the same way.

    voltage clamps( Alvin).pptx
  • 0 in reply to Chris Cockrill
    Prodigy 35 points

    Thanks again Chris!


    I've been studying this slideshow, and part datasheet, but still not quite there yet.

    I'm certain this is the right part for my application though since the datasheet indicates this part works for GPIO, MDIO, PMBus, SMBus, SDIO, UART, I2C, practically it will fulfill all my IO requirements. Also, it supports Hot Insertion, which is a bonus!

    Would you please take a look at the following circuit to test my understanding of what you mentioned in your previous post, and correct the drawing to include the proper way to interface this setup for I2C, SPI, etc? Will the circuit work correctly for I2C as shown?


    Thanks!!

  • 0 in reply to John Artis
    TI__Mastermind 46480 points

    This can work for any signal in the voltage range. frequency is limited to about 100Mhz.

    It is simply a switch until it reaches Vref A and then can be pulled to any othe voltages up to 5.5V