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LM2907-N: Missing equation in application note AN-162

Lester Low
Prodigy 10 points
Part Number: LM2907-N

Hello,

On page 4 of AN-162 I believe there is supposed to be an equation for selection of R1.

It seems to be missing, is anyone able to provide the equation or update the file?

  • 0
    Guru 285740 points

    This equation was already missing twenty years before National was acquired by TI. Whoever wrote this application note in 1976 is no longer available.

  • 0
    TI__Guru* 93105 points

    Hi Lester,

    Certainly the equation for C1 can be transposed to solve for R1, but you would need to have a value for C1 already established. Note that prior to the C1 equation being presented in the AN-162 section "Choosing R1, C1 and C2" there is discussion about three criteria with regards to selecting R1's value. Once they are considered and a value is for R1 is decided upon, that is when the C1 equation is provided which includes the decided upon value for R1. Following this procedure  helps better set a C1 value for more optimized performance from the LM2907-N. Once R1 and C1 are established, then C2 is determined from the C2 equation. 

    If you go through the LM2907-N datasheet you will notice that many of the circuits and examples provided use an R1 of 100 kilohms. That appears to be a value that satisfies a wide range of the applications to which the LM2907-N is applied. However, it is best to follow the three R1 selection criteria in AN-162 and find the value that best fits your application.

    https://www.ti.com/lit/ds/symlink/lm2907-n.pdf

    Regards, Thomas

    Precision Amplifiers Applications Engineering