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TXB0304: VIH question

Lidar Glazer
Prodigy 90 points
Part Number: TXB0304

hi,

I am using ibis model for txb0304. from the datasheet VIH=0.65*VCCA.

In my case VCCA=1.2V, i expect VIH=0.65*1.2=0.78v.

when i simulate it i see that from input signal of 0.5v the level translator is opened. can yo explain how? why isn't it from 0.78v? (i tried all models types - slow fast min max and typ)

see attached the ADS schematics and plot

appreciate your prompt response

Lidar LT_question_for_TI.docxtxb0304.ibs

  • 0
    TI__Guru* 97046 points

    Hi Lidar,

    I believe you are confusing VIH (guaranteed input HIGH voltage) and VT (input threshold voltage). These values are not the same thing. It is expected behavior for a CMOS device to switch at ~0.5*Vcc at the input.

    There's an FAQ that explains this in details located here:

     

    If this answers your question, please click the green "this resolved my issue" button, or if you need further assistance, please respond and I will continue to help.

  • 0 in reply to Emrys Maier
    Prodigy 90 points

    LT_question_for_TI_2.docxwhere can i find the threshold parameter in the datasheet?

    can you guarantee that with input signal with Vpeak=0.6v the level translator will work properly?

    what is the best method to simulate the following: VCCA=1.2v VCCB=1.8v? can you take a look in the attached doc and let me know if i connected the models correctly?

    Thanks!

  • 0 in reply to Lidar Glazer
    TI__Guru 61890 points
    Lidar,

    We do not spec the threshold parameter for this device. Only the Vih and the Vil paramters are mentioned in the datasheet.
    The schmitt trigger device specifies the Vt+/ Vt- for the device. Again, this is not absolute and will have a range ( min and max) to specify across PVT corners. To ensure the device switches, the Vt+max or Vt-min must be applied.