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TLC555: Large periods (Large resistor/capacitor value)

Motoyasu Hattori
Genius 10965 points
Part Number: TLC555

Hi,

My customer wants to count about 2 minutes with TLC555.  To achieve this, you must have multiple resistors in series and multiple capacitors in parallel. Are there any concerns when doing this?

For example, when the time constant is 100 seconds, I think that the theoretical time constant will be the same when R is 10 MΩ and C is 10 μF, and when R is 1 MΩ and C is 100 μF.  Do you recommend which value?

Thanks and best regards,
M.HATTORI.

  • 0
    TI__Mastermind 42043 points

    Hello,

    Are you asking about putting multiple resistors in series and multiple capacitors in parallel in order to get the exact time of 120s? Remember, due to the tolerance on the parts you are using, the time constant cannot be exact. However, there are no other concerns with placing the multiple resistors in series and multiple capacitors in parallel. 

    Higher resistance will eventually lead into leakage problems, but 10MΩ is usually ok. Either combination will work. 

    Best,

    Katlynne Jones