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SN74AUP1G08: Differences between SN74AUP1G08 and SN74AUP1T08

James Dupre
Prodigy 60 points
Part Number: SN74AUP1G08
Other Parts Discussed in Thread: SN74AUP1T08

What are the differences between the SN74AUP1G08 and SN74AUP1T08? According to their respective datasheets, both devices appear to be interchangeable. However, the input voltage requirements for  the SN74AUP1G08 are defined as a single voltage threshold even though this device has Schmitt trigger inputs (according to the Features of the datasheet). By contrast, the input voltage requirements for the SN74AUP1T08 are defined as a range for positive going and negative going inputs which is consistent with the orthodox parameters for Schmitt trigger inputs.

Thanks,

James 

  • 0
    TI__Guru* 96712 points
    Hi James,
    The SN74AUP1G08 is listed as having 'Schmitt-trigger action inputs' which, as you pointed out, does not mean that it has an actual Schmitt-trigger architecture on the inputs. There is some hysteresis designed into the part, but it cannot be used in all the same applications as a real Schmitt trigger. The SN74AUP1T08 has actual Schmitt-trigger inputs, which can be determined by looking for the threshold and hysteresis values in the electrical characteristics table.
  • 0 in reply to Emrys Maier
    Prodigy 60 points
    Thanks for your reply Emrys. As a follow-up question, what is the output of the SNAUP1T08 when it powers on if the input voltage is within the range for both VT+ and VT- (e.g. 0.8V for VCC=3.3V, TA=25C)?
  • 0 in reply to James Dupre
    Guru 272080 points
    In theory, this is undefined.

    But the thresholds are affected by VCC, which will increase gradually. So if the voltage of that input signal is not affected by the power-on event, then the input was unambiguously high at some point of time.
  • 0 in reply to Clemens Ladisch
    Prodigy 60 points

    Thanks Clemens. One last question just to confirm my understanding. Assume that the input voltage is high (e.g. 3.0V while VCC is stable at 3.3V, TA=25C) and then it switches low but settles at voltage somewhere between V(-)min and V(-)max (e.g. 0.6V). In this case, the output *may* remain high but also may switch low, correct? The output state will vary from device-to-device.

  • 0 in reply to James Dupre
    TI__Guru* 96712 points
    Hi James,

    Your understanding is correct. The negative-going threshold has a range of possible values, so there is no way to be sure that your signal has crossed the threshold unless it drives all the way down to the minimum threshold value.

    If you have an application where the threshold values are extremely important, I would recommend designing it around a comparator instead of a Schmitt-trigger.