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SN74AUP1G08: Noise on SN74AUP1G08 input

Jie Wang
Prodigy 110 points
Part Number: SN74AUP1G08

Tool/software:

Hi, TI expert

SN74AUP1G08 is used on our board. VCC is 3.3V.  We measured big high-frequency noise on the input pins of SN74AUP1G08, see the picture below. The big noise makes the dip of the Vhigh min voltage reaches to ~1.9V which is lower than the VIH min (2V), but the dip below 2V is very short, about ~1ns. Will the output response to this short dip?

  • 0
    Guru 316780 points

    The actual switching threshold should be near VCC/2, so this is unlikely. But there is no guarantee.

    2.5 V noise is quite a lot, and it is dangerously close to reaching VCC/2. You should use better board layout, a low-pass filter, and/or shielding to remove that noise.

  • 0 in reply to Clemens Ladisch
    Prodigy 110 points

    Thanks for your reply. We will try to filter the big noise later. We have some existing board that we can't add the filter now. 

    From the spec, there is 1.5pF input capacitor inside SN74AUP1G08. The noise we measured is about 180MHZ, will the input capacitor inside be capable of filtering this high frequence noise?

  • 0 in reply to Jie Wang
    Guru 316780 points

    There is no separate capacitor; the Ci specification describes the capacitance of the MOSFET gates. (Dis)charging this capacitance is what causes the device to switch.