Author Topic: I Need help understanding data sheet math  (Read 374 times)

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Offline ptricks

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I Need help understanding data sheet math
« on: October 20, 2021, 12:02:23 pm »
I'm working with the IC LX27901 and have a situation where the circuit does not operate unless an oscilloscope probe is touching the pin that sets the operating frequency, the frequency set by an RC circuit.
The data sheet section below shows how to determine the correct values but I am not understanding how they are doing the math, mainly the notation with the .94 and .91 above the values. It has been about 30 years since math classes so maybe I need a refresher.

 

Offline RoGeorge

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Re: I Need help understanding data sheet math
« Reply #1 on: October 20, 2021, 12:30:03 pm »
Unless specified otherwise, that notation usually means "to the power of", in programming languages the symbol is either "^" or "**", on a pocket calculator is the \$ X^Y \$ key.  For example \$ 330 ^ {0.91} \approx 195.82 \$

Where did you get that pdf?  I've searched for LX27901, and this datasheet is the first result returned, with a different formula, http://www.microsemi.com/document-portal/doc_download/125192-lx27901-datasheet

\[ f_{SW} \approx \frac{693000}{R_{C\_R} \cdot C_{C\_R}}\]
« Last Edit: October 20, 2021, 12:32:59 pm by RoGeorge »
 
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Online xrunner

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Re: I Need help understanding data sheet math
« Reply #2 on: October 20, 2021, 12:31:03 pm »
Look at the attached, seems top use a clearer equation for the calculations.
[hp] Hewlett . Packard
 

Offline Brumby

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Re: I Need help understanding data sheet math
« Reply #3 on: October 20, 2021, 12:32:35 pm »
They look like power notation.

For example, the denominator would be: (RC_R)0.94 x (CC_R)0.91
« Last Edit: October 20, 2021, 12:34:08 pm by Brumby »
 

Offline ptricks

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Re: I Need help understanding data sheet math
« Reply #4 on: October 20, 2021, 12:43:54 pm »
Looks like the data sheet I had was the first version from 2011.  They did change it in 2012 which is much easier to understand. Thanks didn't know about that.
 


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