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TXB0106 with pull-up resistors

Peter Malm
Prodigy 170 points
Other Parts Discussed in Thread: TXB0106, SN74AVC8T245, LSF0108

Hi,

I am trying to use the TXB0106 as level shifter on an SDIO-bus between a 3.3V host and a 1.8V peripheral. I would like to use a pull-up resistor on the cmd line for example, but it seems as if the circuit doesn't work with that. I put a 56k pull-up to 1.8V on one of the 1.8V side input/outputs, but if I then measure the voltage at the pin it is not 1.8V, but more like 0.3V. Shouldn't it be possible to define a logic high level like that with the TXB0106? 

  • 0
    TI__Intellectual 2530 points

    Hi

    When using an auto direction sensing translator, the value of the pull-up resistors must be kept high enough to ensure that they do not contend with the weak outputs of the translator. For card interface applications using auto direction- sensing translators, use the highest allowable pull-up resistor value of 100k.

    Also, the driver driving the part must have drive strength of at least +/- 2mA.

    Thanks

  • 0 in reply to Jennifer Joseph
    Prodigy 170 points
    Hi Jennifer,

    Thanks for the answer. In the datasheet it says that if pull-ups are needed,they should be larger than 50k, so I took 56k. I will try 100k as well. But if I want to define the static default level on a pin (without drive) to be either high or low using pull-up or down, is that possible with this circuit or not, or should I use something else?
  • 0 in reply to Peter Malm
    TI__Intellectual 2530 points

    Hi Peter

    -As stated in the datasheet, for proper operation, the device driving the data I/Os of the TXB0106 must have drive strength of at least ±2 mA. The fet based auto-direction sensing parts TXS010x also require an open-drain or a push pull driver with minimum source/sink capacibility in order ot achieve the VIL/VOL levels.

    -One other option is to use a direction controlled part such as SN74AVC8T245.

    One obvious drawback of this fully buffered solution is the multiple processor GPIOs needed for the direction signals (DAT0-dir, DAT123-dir and CMD-dir) that control the data and command lines. The additional software programming required to properly set the processor signals may also be a disadvantage of implementing this method of level translation.

    -Else, you can take a look at the LSF0108.

     

    Thanks