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Original question:

[FAQ] How do I design a-stable timer, oscillator, circuits using LMC555, TLC555, LM555, NA555, NE555, SA555, or SE555?

LMC555: What is the main cause of VCTRL and VTRIG voltage variation?

Kazuya Nakai59
Guru 20780 points
Part Number: LMC555

Hello guys,

One of my customers is considering using LMC555 for their new products.

At this moment, they have the following question.
Could you please give me your reply?

Q. VCTRL and VTRIG voltage have about +/-10% variation. I think these variations are main cause of Astable Frequency variation (+/-17%).
     What is the main cause of VCTRL and VTRIG voltage variation? Is it internal ladder resister variation?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Mastermind 22620 points

    Hi Kazuya, 

    Generally the largest error will come from the external timing capacitor tolerance. Internally there is a resistor divider as shown below that contributes to the variation in addition to the offset voltage of the lower comparator that the trigger pin is tied to. 

    Best Regards, 

    Chris Featherstone