SN74LVC1G66: capacitance leakage from input to output.

Dharmesh Joshi

Part Number: SN74LVC1G66
Other Parts Discussed in Thread: SN74LVC2G66

Dear All

I am trying to use a SN74LVC1G66 with my PCB capacitance sensor .

The aim is to completly issolate the electrode from the rest of the circuit for calibration purpose.

When the SN74LVC1G66 is switched off , its seems as a little capacitance is still effecting it as when i touch the PCB electrodes a very small change is noticed.

Is a SN74LVC1G66 the correct IC to use for an isolation requirement?

Thank You

over 6 years ago

0 Fan.Wang over 6 years ago

TI__Intellectual 2900 points

Hi DJ,

Would you share the system level diagram with us and explain what you are concerned? I will be able to analyze your system and see if SN74LVC1G66 is a good fit.

0 Dharmesh Joshi over 6 years ago in reply to Fan.Wang

Expert 1785 points

Will a block diagram be ok at this stage?

0 Dharmesh Joshi over 6 years ago in reply to Dharmesh Joshi

Expert 1785 points

Hope you got my diagram.

When the switch is OFF the sensitivity of the electrode is far less and but it still detects.

Maybe the reading are proportional and i can use the difference in percentage of when its off and on for my final value.

0 Fan.Wang over 6 years ago in reply to Dharmesh Joshi

TI__Intellectual 2900 points

Hi Dharmesh,

I am glad that you have proved the concept on your proto board. Please feel free to contact us back any time you need further help.

0 Dharmesh Joshi over 6 years ago in reply to Fan.Wang

Expert 1785 points

I got another question that related to the same topic.

I would like to measure the temperature in same regionas my Capacitance electrode.

Would it be a good idea to USE another switch in parallel to discussed switch but connecting the GND from my temp IC to the same Electrode?

I aware that both switches can never be ON at the same time.

0 Fan.Wang over 6 years ago in reply to Dharmesh Joshi

TI__Intellectual 2900 points

Hi Dharmesh,

You can definitely achieve measuring both temperature and capacitance at the same time by turning on and off of two SPST switch. The switch you may consider is 2-channel SPST. SN74LVC2G66 is an example.

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SN74LVC1G66: capacitance leakage from input to output.