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LMC555: Revision M to N (Changing the value of Ra and Rb)

R.Fukunaga
Expert 1545 points
Part Number: LMC555

Tool/software:

Hi all,

About the changes from Revision M to N (Changing the constants of Ra and Rb).

I think the waveform period changes from about 150 μs to 70 μs depending on Ra to Rb.

Am I correct in understanding that the reference resistance was changed for this consistency?

Revision M

Revision N

Best Regards,

Ryusuke

  • +1
    TI__Intellectual 1570 points

    Hello Ryusuke-san,

    Yes, you are correct. The values of RA and RB in this figure were updated so that the waveform in the figure matches the calculated results. In revision M, where Ra = 3.9kΩ, Rb = 9kΩ, C = 0.01μF, the calculated period of the output is 152.08μs, while the figure shows a period of around 70μs.

    To fix this discrepancy, Ra and Rb were changed in revision N to be 1.78kΩ and 4.12kΩ, which results in a calculated period of 69.58μs that matches what is shown in the figure. Let me know if you have any additional questions about the LMC555, and I'd be happy to answer them.

    Best Regards,

    Alex Curtis