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SN74LVC1G17: input bias current, max values

Ue
Genius 17185 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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  • 0
    Guru 317730 points

    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.

  • 0 in reply to Clemens Ladisch
    TI__Genius 17185 points

    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

  • 0 in reply to Ue
    TI__Guru* 97066 points

    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.

    Ue said:
    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.