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TXS4555: Pull Up/Pull Down Resistors

John Garrett
Expert 4210 points
Part Number: TXS4555

Does the TXS4555 require pull-up/pull-down resistors or are they integrated?  The EVM doesn't show any pull-up/pull-downs but the data sheet references them in the electrical table on the top of page 7:

RI/OPU I/O pull-up                  16 20 24 kΩ

RSIMPU SIM_I/O pull-up         10 14 18 kΩ

RSIMPD SIM_I/O pull-down SIM_CLK, SIM_RST, SIM_I/O when EN = 0        3 kΩ

Please let me know.

Thanks, John Garrett TI-AFA

  • 0
    Guru 243680 points
    "Electrical characteristics" describe properties of the device itself; any required properties of the external circuit would show up in the "recommended operating conditions".
    So these values are for the integrated pull-up/-down resistors.
  • 0 in reply to Clemens Ladisch
    TI__Expert 4210 points

    OK - thought so but wanted to confirm.

    Also for clarity, please confirm, no external pull ups or pull downs are needed for the level translator inputs and outputs or any other I/O's.  I'm following up bec VOL is defined with IOL=1mA and this doesn't necessarily correlate with the integrated pull-ups:

    SIM_RST          IOL = 1 mA              1.65 V to 3.3 V 1.8 V / 2.95 V (2)  VSIM × 0.2 V

    SIM_CLK          IOL = 1mA                                                                      VSIM × 0.2

    SIM_I/O            IOL = 1 mA                                                                                  0.3

    I/O IOL = 1 mA                                                                                                     0 .3

    Thanks, John Garrett, TI-AFA. 

  • 0 in reply to John Garrett
    Guru 243680 points
    The I/Os are designed that way to work with SIM cards. I'm not a TI employee, so I don't know why you would suspect that somebody put a wrong resistor value in there … :-J

    "IOL = 1 mA" means that the pin sinks 1 mA. With an internal pullup, the actual output driver must sink more current, but that is already taken into account (and the current from the pullup is much smaller anyway).

    I'd guess that the actual circuit does not actually require 1 mA, and that these test conditions were just copied from the ISO standard.