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TXS0104E: What's the valid input range for VIH if VCCA set to be 1.8V?

Max Guan
Intellectual 1350 points
Part Number: TXS0104E
Other Parts Discussed in Thread: SN74AXC4T245

team,

Below is customer schematic:

The plan is to support 1.8V input from portA and output to portB @ 3.3V. A question that cusotmer input side voltage may as low as 1.13V as GPIO high output. Will our device be able to support the application?

Based on datasheet claim, seems the valid VIH min is 1.6V with VCCA=1.8V. Will it be concerning? (not sure why but customer mentioned the competitor device with the same claim could support 0.5VCC as input high, so I would expect similar performance if it is really the case)

Thanks

Max

  • 0
    Guru 263000 points

    The TXS uses a pass transistor whose gate voltage is at VCCA. For any voltages that are more than the threshold voltage below VCCA (about 1.2 V in your case), it works as an analog switch, so the B output will also be 1.13 V.

    All of your signals are unidirectional, so you should use a buffered level shifter like the SN74AXC4T245, which also allows a lower supply voltage.

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 1350 points

    Hi Clemens, 

    Sorry I'm a little confused, please allow me re-describe the question and my understanding, the question as below, to confirm if the TXS could recognize 1.13V as a logic high input? And if A input is 1.13V what will be on output B?

    Because 1.13V is not reaching the VIH_min (1.6V) defined in datasheet, I'm not sure is it meeting your mentioned condition? Will the output to be 1.13V if the input is 1.13V with VCCB contected to 3.3V?

  • 0 in reply to Max Guan
    Guru 263000 points

    There is no "logic high" or "logic low" because the TXS is not buffered and has no switching threshold.

    The gate bias is VCCA. When the A voltage is above 1.6 V, the transistor is guaranteed to be off, and the B voltage is determined by the pull-up resistor. When the A voltage is below 0.15 V, the transistor is on, and the B voltage is guaranteed to be below VOLB (see the electrical characteristics). For voltages between VIL and VIH, the transistor might be on, and the B output will probably not be below VOLB or above VOHB.

    The graph on page 1 of the datasheet describes this behaviour.