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LSF0102: Level translator for 1-Wire lines

Mihai Vintila
Intellectual 590 points
Part Number: LSF0102
Other Parts Discussed in Thread: PCA9306, , TXS0102, TXS0101

Hello, I have to make a level translation from 3.3V to 5V on a 1-Wire bus (I have two 1-Wire lines on the board).

I have found several parts that seem suitable and I would like to make sure I make the right choice.

I believe LSF0102 should be good, otherwise  TXS0102E seem to be a possible choice too. I have considered also PCA9306, even if it is targeted to I2C I believe it should work too, is that correct ?

Is it OK to use LSF0102 for this function ?  Or is there a better option ?

Thanks,

Mihai

  • 0
    TI__Mastermind 45145 points

    Hi Mihai,

    Yes, these devices can support bi-directional open-drain translation up to 5 V. If this is how the 1-wire bus operates, then I see no issues using any of the 3 mentioned devices. If you plan to use your own pull-ups I recommend the LSF0102. TXS0102 will have internal 10K pull-ups and won't need external pull-ups on the line.

  • 0 in reply to Dylan Hubbard
    Intellectual 590 points

    Hello Dylan, many thanks for the very fast response.

    The situation is a bit more complicated as the customer requires to support also 3.3V on the "translated" side.

    So the device must connect to 3.3V on the microcontroller side (A side) and support both 5V and 3.3V on the "translated" side (B side).

    I have looked in more detail at the LSF0102 and it is required to have on the B side a voltage higher by approx 1V than the A side.

    Is there a device (from these three options above or other ones) that can support this function ?  As I understand the TXS0102 supports also operation with VCCA=VCCB ?  It would be better to have external pull-ups but we can consider also a solution with internal pull-ups.

    Thanks,

    Mihai

  • 0 in reply to Mihai Vintila
    Guru 298840 points

    The LSF requires oly that the two VREF voltages are different. If you have a 5 V supply, you can also use it with 3.3 V data.

    But for low-speed signals, there is an easier way to use the LSF: data at A1/B1 (with pull-up resistors on both sides), leave Vref_A/B open, and connect EN directly to the lowest supply.

  • 0 in reply to Clemens Ladisch
    Intellectual 590 points

    Hello, thank you for your response, you wrote "The LSF requires only that the two VREF voltages are different" but the issue is that - as I wrote above - we can have also the situation that both VREF voltages are the same (3.3V). 

    Also for the second point that you mentioned  "connect EN to the lowest supply."  - if we have 3.3V on both sides I believe this would not work, is that correct ?

    Thanks,

    Mihai

  • 0 in reply to Mihai Vintila
    Guru 298840 points

    If your B supply is not higher than 3.3 V, then you cannot connect it to Vref_B.

    That restriction applies only if you are using the Vref pins. If you leave the Vref pins open and connect EN directly to the 3.3 V supply, then all signals can be as low as 3.3 V (but the switch capacitance is higher).

  • 0 in reply to Clemens Ladisch
    Intellectual 590 points

    Hello, I have updated the device to TXS0101 as this one should support also the case with the same voltage on both sides and it seems more straightforward to use.  If we need a smaller pull-up we will add external pull-up in parallel with the internal 10K.

     I believe this should work fine for this application, can you please confirm ?

    Thanks,

    Mihai

  • +1 in reply to Mihai Vintila
    Guru 298840 points

    Yes, it should work.

  • 0 in reply to Clemens Ladisch
    Intellectual 590 points

    Thank you very much for your support !