### Author Topic: how to interpret formulas in datasheets  (Read 545 times)

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#### autotel

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##### how to interpret formulas in datasheets
« on: August 04, 2020, 04:39:19 pm »
Often when I see a datasheet's recommended diagrams, I find that the formulas make no sense. Are formulas written in a different way when speaking about electronics?

for example, this datasheet: https://statics.cirrus.com/pubs/proDatasheet/CS4334-5-8-9_F7.pdf
has the formula: [attach=1]

I can graph it and it works, but it has a parentheses that seems to have no reason, and it makes me very suspicious about how I am interpreting it. (my interpretation is:
Code: [Select]
x=(y+560)/(4*pi*44100*y*560), Fs being 44100)

#### Benta

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##### Re: how to interpret formulas in datasheets
« Reply #1 on: August 04, 2020, 05:12:59 pm »
Your interpretation is correct. Unfortunately many US manufacturers invent their own symbol language far away from normal notation. Not to speak of ignoring SI units.

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#### autotel

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##### Re: how to interpret formulas in datasheets
« Reply #2 on: August 04, 2020, 06:03:05 pm »
thank you!
But what about the parenthesis? just a whim? or maybe is to separate the characters?

#### TimFox

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##### Re: how to interpret formulas in datasheets
« Reply #3 on: August 04, 2020, 06:16:15 pm »
In usual algebraic notation, two factors side by side are to be multiplied, as in "A X".  However, normally one says "560 RL" instead of  "RL 560" when one of the factors is a number.
Note that the occurences of RL and 560 are the normal expression for the parallel conductance of two resistors, and the parentheses match.  Therefore, this is an awkwardly written formula, but not technically incorrect.
« Last Edit: August 04, 2020, 06:18:51 pm by TimFox »

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#### Benta

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##### Re: how to interpret formulas in datasheets
« Reply #4 on: August 04, 2020, 06:40:02 pm »
What you have to realize is, that engineers hate writing data sheets and application notes. This is often left to interns during the summer vacation. I should know, I've worked in the semiconductor industry for over 40 years.

Large companies like TI have this under control, their documentation is generally of a very high quality, being maintained by professional technical editors.

But others, in this case Cirrus, apparently leave it as it is and rely on the product and application engineers to catch the issue when it comes up. This is fine for major customers who get a lot of attention, but bad for the little guy.

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#### wizard69

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##### Re: how to interpret formulas in datasheets
« Reply #5 on: August 04, 2020, 07:19:45 pm »
Often when I see a datasheet's recommended diagrams, I find that the formulas make no sense. Are formulas written in a different way when speaking about electronics?

for example, this datasheet: https://statics.cirrus.com/pubs/proDatasheet/CS4334-5-8-9_F7.pdf
has the formula: [attach=1]

I can graph it and it works, but it has a parentheses that seems to have no reason, and it makes me very suspicious about how I am interpreting it. (my interpretation is:
Code: [Select]
x=(y+560)/(4*pi*44100*y*560), Fs being 44100)

It looks OK but a suggestion, when coding up things that look questionable to you or may need manipulation, maintain the supplied naming conventions.   If something ends up causing computational problems it is easier to go back to the reference and evaluate either that or your code.

A for your issues with the parenthesis I'm not sure what the issue is.   They effectively group operations but they can also improve clarity.    In this case I suspect that clarity was the goal as they effectively separate out the variables Fs and RL which is probably a good practice.    The alternative is writing: Fs * RL using an explicit multiplication symbol.   The other way to look at this is what might happen if it is 3:00am and you only have one eye open, looking at your code and the expression in the data book.   It could be especially confusing if there is a parameter called FsR someplace.

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#### TimFox

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##### Re: how to interpret formulas in datasheets
« Reply #6 on: August 04, 2020, 07:22:04 pm »
Perhaps the intern's native language was not mathematics, so he was awkward but not actually incorrect.

#### newbrain

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##### Re: how to interpret formulas in datasheets
« Reply #7 on: August 05, 2020, 07:11:02 pm »
In this particular case, the added parenthesis was possibly put on purpose, to make it stand out that RL is in parallel with a 560 ohm resistor.

It looks like the way to determine the capacitance for a -3 dB frequency of Fs, in an RC circuit, where R = RL//560

Not that I can see it, so just a supposition.
« Last Edit: August 05, 2020, 07:13:18 pm by newbrain »
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