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TXB0104: Input Driver Requirements for TXB

dimitry chen
Expert 1145 points
Part Number: TXB0104


Hi

In Datasheet , 8.3.2 Input Driver Requirements

it says " TXB0104 device must have drive strength of at least ±2 mA "

how do you get this value ?

base on Figure 9.,  I don't know how to calculate the value of  drive current.

can you explain for me ?

and if current is less than 2mA, what is the side effect, thanks

  • 0
    TI__Guru 62390 points
    Hi Dimitry,

    I would like to know the translation requirements for your application.
    Since the TXB is auto bidirectional device, it has a weak buffer based architecture. In order to have the outputs toggle , the input must overpower the driver to switch from low to high or high to low.
    The worst case for switching the 5.5V output to 0V will require about 1.4mA drive current to overdrive the 4k buffer, but will have some operating margin included for reliable switching.
    with the translation voltage levels lower than 5.5V, the drive current will scale down as well linearly. for eg, 3.3V translation would require ~1.2mA of input drive requirement.
  • 0 in reply to ShreyasRao
    Expert 1145 points
    Hi

    My design

    TXB input side , 1.8V , output side 3.3

    main chip send 1.8V level signal to TXB , change to 3v3 level

    I try to calculate the TXB input current by figure 9.

    (1.8/2 + 3.3 )/ 4k = 1.05mA

    is that mean my main chip need out at last 1.05 mA ?
  • 0 in reply to dimitry chen
    TI__Guru 62390 points
    Dimitry,
    I will go by the recommended drive strength of 2mA as suggested by the datasheet being the worst case for 5V case(5.5V being the 10% deviation), along with a reasonable margin included.
    so, for 1.8V input, it will scale down to about 0.72mA.
    Is this supported by your host? what is the drive strength?