LMC555: How to estimate minimum value of the tH period.

Motoyasu Hattori

Part Number: LMC555

Hi,
My customer has the following questions.

1) Data sheet said that tH = 1.1xRAxC on Section8.4.1. Is "1.1" a typical value?

2) Also, we can find the sentence "at the end of which time the voltage equals 2/3 Vs" on section 8.4.1 of the datasheet. Is this 2/3 also a typical value?

My customer wants to estimate what the minimum value of the tH period will be, and we want to know what to think about other than the variation between C and R.

Thanks and best regards,
M.HATTORI.

over 5 years ago

0 Former Member over 5 years ago

Hattori-san,

Thank you for your question and my apologies for the delay in response.

Please allow another 24 hours for me to look into this. Thank you.

Regards,

Daniel Miller

0 Former Member over 5 years ago in reply to Former Member

Hattori-san,

Thank you for your patience. Here are the answers to your questions.

The 1.1*R*C value and the 2/3 Vs value are both inherent to the structure of the circuit. For example, the 2/3 Vs value is derived from the fact that three equivalently sized resistors are used as voltage dividers within the part to set the timing thresholds.

The primary variation will be caused by the capacitor as these are typically the components which differ the most from their nominal value, as I am sure you are aware. For further guidance regarding accuracy, please consult the "Accuracy" section of this FAQ.

Regards,

Daniel Miller

0 Former Member over 5 years ago

Hello Hattori-san,

Since, I have not heard back from you in a while, I am going to assume that your question has been answered sufficiently.

If you need further help or feel that the issue is still unresolved, please feel free to comment here again or begin a new thread.

Thanks,

Daniel Miller

Clock & timing

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LMC555: How to estimate minimum value of the tH period.