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TXS0108E: To know Input sinking and output sourcing current

shanthi s
Intellectual 420 points
Part Number: TXS0108E
Other Parts Discussed in Thread: SN74LVC8T245, SN74LVC16T245

Hi,

I have a plan to use TXS0108E voltage level translator IC to converting 3.3V to 5V.

I have needed the following function so i have selected this IC,

Input

Output

High

High

Low

Low

No connection

High

I am not adding any external resistors, I need to know two things,

1. IN1 - IN8 (A port) signals input sinking current for operation?

2. OUT1 - OUT8 (B port) signals min, max output sourcing current ?

Please reply to the question as soon as possible.Thanks in advance.

  • 0
    TI__Guru 62050 points
    Hi Shanti,

    The TXS is a passive device which doesn't provide any DC sinking or sourcing current of its own.
    The output IOH is 20uA and IOL is ~ 400ua through the pull-up resistor.
  • 0 in reply to ShreyasRao
    Intellectual 420 points

    Hi ShreyasRao,

    In the parametric field you have given that drive max 50ma. What the 50ma represent?

    I would like to get atleast 5ma output current to turn on the LED. Is there is a possible to get 5ma output?

  • 0 in reply to shanthi s
    TI__Guru 62050 points

    Shanti,

    That is not right. I will take note of this and update with the right values.

    We are also in the process of coming up with updated parametric search to help customers like you to enable easier navigation and searching to narrow down to the required devices quickly.

    Any inputs are appreciated in this regard.

    5mA drive current cannot be supported by TXS0108E.

  • 0 in reply to ShreyasRao
    Intellectual 420 points

    Hi ShreyasRao,

    For the 5mA-8mA output drive current, shall I use 74LVC8T245 with external pull up resistor at the input side? Is it suitable  or is there any considerations?

  • 0 in reply to shanthi s
    TI__Guru 62050 points
    Yes, the SN74LVC8T245 supports up to 32ma of drive.
    pullup at the input side is not required unless the interface is open drain.
  • 0 in reply to ShreyasRao
    Intellectual 420 points
    Hi ShreyasRao,

    Yes, am using open drain input signal. Please see the function table in the first question for reference.
    For using SN74LVC8T245, how much total operating current required from both VccA(3.3V), VccB(5V) to provide a proper output for all 8 signals?

    Thanks.
  • 0 in reply to ShreyasRao
    Intellectual 420 points
    Hi ShreyasRao,

    Yes, am using open drain input signal. Please see the function table in the first question for reference.
    For using SN74LVC8T245, how much total operating current required from both VccA(3.3V), VccB(5V) to provide a proper output for all 8 signals?

    Thanks.
  • 0 in reply to shanthi s
    TI__Guru 62050 points
    Hi Shanti,

    It depends on the pullup resistors used.
    I will , however, mention here that the pullup resistor must be such that the input rise time/ fall time is sufficient for the device to handle so that the output does not cause any unwanted behaviour or oscillations.
    You could start with using 1K pullup at the input.
  • 0 in reply to ShreyasRao
    Intellectual 420 points
    Hi ShreyasRao,

    I have using 4.7K resistor at the input side pull up.
    I want to choose the power supply regulator (1A or 3A) depends on the total load current of the circuit.
    So I need to know the current required to operate and generate the outputs in 74lvc 8t245 IC. In my design i have used 8 voltage level translator(74lvc8t245) IC.
    Thanks
  • 0 in reply to shanthi s
    TI__Guru 62050 points
    Hi Shanti,

    1A regulator is sufficient for operation of all the 8 ICs in your design.
    3.3V/ 4.7k = 0.7mA of current (only during low cycle) per input and with 64 inputs you will see about 45mA of current.
    The transient/dynamic switching will also consume current, however it will not go beyond 1A overall for all the 8 ICs combined.

    have you also considered using 4 * SN74LVC16T245 device to reduce the overall numbers of ICs?
  • 0 in reply to ShreyasRao
    Intellectual 420 points
    Hi ShreyasRao,

    Thank you for the information. Ya i noticed about sn74lvc16t245, but sn74lvc8t245 is apt for my design to place in the board.

    Am using 1A,5v out regulator for supply voltage. In my design i have used other circuits + 8 no of sn74lvc8t245. The other circuit may consume around 500mA. So I need to know required operating current for the ic sn74lvc8t245 from the supply volt 5. Based on this i want to decide about the power supply. How much current required for one sn74lvc8t245 ic working fine with all the 8 input,output signals? This information is not clear in the data sheet. Please provide a answer as soon as possible.

    Thanks in advance.
  • 0 in reply to shanthi s
    Intellectual 420 points
    Hi ShreyasRao,

    Please Let me know if there is any update for my question.
  • 0 in reply to shanthi s
    TI__Guru 62050 points
    Hi Shanti,

    The datasheet only gives the Icc quiscent current spec, the dynamic current is not given and would depend on various factors of input / output switching frequency, loading cap, number of simultaneous switching taking place etc.
    Overall, I can say with a fair bit of certainty that 1A regulator will be able to handle the 8 LVC8T245 device without issues.