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TXB0102: Any single IC solution 2-bit interface to shift level between 3.3v and 5v in fixed opposite directions (not auto-sensing)?

Vlad Blanshey
Intellectual 690 points
Part Number: TXB0102
Other Parts Discussed in Thread: SN74LVC2T45, TXU0204, SN74AVC2T245, SN74AXC2T245, TXU0202

Hello,   I am searching for a 2-bit interface solution, unidirectional, dual power source, non-autosensing, Push-Pull,  for UART and for proprietary sensors interfaces. The MCU side is 3.3v CMOS logic while IO device is 5V CMOS.

As in UART case so is in other sensors : one line is MCU output, another MCU input. All directions are fixed. Simple. Typical UART-like application you might say.

What a surprise for me after days of search returned nothing to have in a single package . The package I need is SOT23-6 or similar with 0.96mm between pins (worse case 0.65mm would be acceptable).

Tried the TI's  SN74LVC2G07DBV single power supply yet converts both UP and DOWN with proper pull-up. Open drain gave too slow rising edge unless pullup is too strong for a reasonable power consumption.

Tried TI's   TXB0102 dual power with auto-sensing for a direction.  Because of having long lines with hard to clean EMI , all auto-sensing chips oscillate - impossible to fight. The "sensing" part of them is quite "sensitive" - gets triggered easily by EMI spikes.

Good solution is TI's   SN74LV1T34DBV  which is a single bit one-way push pull level converter. Depending of the power supply it converts to whatever level output yet input is tolerant of up to +5V.  If a single package solution for 2-bit (1 output and 1 input) is not found, we will use two chips for a single interface. Surely too many traces and pins on PCB for such a simple single interface like UART...

Considered a nice chip from TI   SN74LVC2G17DBV which has Schmitt trigger at the inputs (very useful in noisy lines)... unfortunately this converts only in DOWN level from 5v to 3.3v , not UP.

May be I am missing something, 'cause it is hard to believe that there is no push-pull 2 power supplies a level shifter between 3.3v and 5v . Even half a century old UART interface is recommended to implement using open drain with pullup resistors with slow rising edges , or, otherwise with new "auto-sensing" which is only good for short lines on PCB, not for cables...

The interface conversion between 3.3v and 5v is also quite old requirement in the development based on CMOS chips... and UART has been running long lines in many applications so the new "auto-sensing" could not be recommended for that...

Please advice... I still hope that TI has a solution but I am missing it...

 

  • 0
    Intellectual 690 points

    Forgot to add the analysis of other chips which TI recommended in other similar posts:

    the recommended SN74LVC2T45  is a converter of both lines in either UP or DOWN direction , the direction of both lines is the same. This cannot be recommended for UART for ex. because the UART lines are opposite directions RX and TX .

    the recommended TXU0204  is a 14-pin overkill for only 2-lines interface, by a comparison, even using 2 small chips like SN74LV1T34DBV  is simpler and cheaper solution.

    I know that this topic was already coming up years ago but may be by now TI came up with a new offer for a 2-directional push-pull converter/shifter .

  • +1 in reply to Vlad Blanshey
    Guru 244360 points

    Two-channel translators with two direction pins have "245" after the "T". Unfortunately, there aren't many, and only up to 3.3 V: SN74AVC2T245, SN74AXC2T245.

    The best choice is the TXU0202 (when it is available).

  • 0 in reply to Clemens Ladisch
    Intellectual 690 points

    Thank you Clemens. Indeed TXU0202 did not appear on my radar because supplier does not have it, it is the perfect setup for the UART long lines and all alike interfaces. The 3.3v is too vulnerable against EMI, parasitic line capacitance and mismatched impedance of long lines, 5V will always be preferred in such cases.

    Unfortunately, even when TI start supplying TXU0202 , it's first packaging will not be prototype-friendly. X2SON (DTM) packaging is only good for a mass production. TI also shows in datasheet VSSOP (DCU) packaging, probably for the future, but 0.5mm pitch between pins is very hard for prototyping.  I think, when starting production of any new chip, it is logical to start from such a packaging which is prototype-friendly and still later can be used for production as well. Starting from the packaging which is only good for mass production is not good idea.

    Looks like for years to come the best solution still using two chips push-pull SN74LV1T34DBV , one TX from MCU to 5V sensor (powered by 5V) and another RX from sensor (powered by 3.3v).

    Another good solution to replace receiving chip (RX) with SN74LVC2G17DBV (powered by 3.3v, Schmitt input from 5V line) and enjoying the full pin-to-pin compatibility between those alternative chips (SN74LV1T34DBV and SN74LVC2G17DBV ) .

    Although your input did not change our situation but your information accurately depicts the situation today and that was the purpose of the post.

    Thanks again Clemens.