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SN74LVC1G17: input bias current, max values

Genius 17175 points
Part Number: SN74LVC1G17
Other Parts Discussed in Thread: SN74AUP1G17, SN74LVC1G123, TS5A23157-Q1

Hi all

My customer is looking at the SN74LVC1G17 and they find the input bias current max values of +/-5uA are a problem in their application.

They have an RC in front of this schmitt trigger to generate a large and accurate time constant (safety function), therefore they have to use a COG/NPO capacitor and a large resistor as larger value COG/NPO capacitors are not available or would be too bulky / too expensive. In this situation the +/-5uA affect the accuracy of the time constant.

Can you comment as to the reason for this large tolerance ? ... and comment as what the conditions are when to expect these max values ?

Can you recommend another solution or another device with a lower value for max input current ?

Best regards

Ueli

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  • That value is for the worst case at the most extreme temperature. If you can guarantee that you will stay below 50 °C or so, the leakage will be much lower.

    The SN74AUP1G17 has much lower input leakage current.

    But please note that Schmitt-trigger logic gates have very loose specifications for the switching threshold. If you want higher accuracy, you should probably use something like the SN74LVC1G123.

  • Hi Clemens

    Thank you for the quick reply and for pointing to the AUP family, these are helpful comments.

    Hopefully the above chart should be labelled "uA", otherwise it might be a bit scary for my customer ....Blush...

    Best regards

    Ueli

  • Hi Ueli,

    Note that the plot above is not for the SN74LVC1G17 -- it is for the TS5A23157-Q1. I do expect that the units are incorrect -- I doubt a CMOS switch has 95 A of leakage current at the input Slight smile.

    to generate a large and accurate time constant (safety function)

    If accuracy is required, I would recommend against using an RC + Schmitt-trigger logic gate. The input thresholds of a logic device will be fairly wide.

    I would recommend to look into a comparator + voltage reference to give the most accurate timing based off an RC.