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Noob datasheet question
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Noob datasheet question
l3v3l6
I'm self leaning how to design PCBs and I need to create some components. Looking at the datasheet for a component I see in the package dimension description, size values with a number over another number like this.

5.11
-----
4.90

Does this indicate the maximum and minimum values for a dimension?
Pelsea
Might be. What datasheet are you looking at? Do those values make sense for what is measured? There should be an explanation somewhere. Sometimes two numbers are inches or mm.
l3v3l6
Pelsea wrote:
Might be. What datasheet are you looking at? Do those values make sense for what is measured? There should be an explanation somewhere. Sometimes two numbers are inches or mm.


http://www.ti.com/lit/ds/symlink/mc79l.pdf

I couldn't find an explanation in the datasheet. It says all measurements are metric. In particular I'm asking about the TO-92 package.
devinw1
Generally if you see two numbers high and low that are close, they are limit dimensions. So, a way of expressing the tolerance. ie: 1.5mm +/- .25mm is equivalent to 1.75mm/1.25mm expressed as a limit.

You may, as Pelsea said, see dual units stacked as such, but generally one will be in brackets like this: 0.1" / [2.54mm]. And obviously there will always been the 25.4mm per inch factor between the two so that is pretty easy to figure out.
l3v3l6
devinw1 wrote:
Generally if you see two numbers high and low that are close, they are limit dimensions. So, a way of expressing the tolerance. ie: 1.5mm +/- .25mm is equivalent to 1.75mm/1.25mm expressed as a limit.

You may, as Pelsea said, see dual units stacked as such, but generally one will be in brackets like this: 0.1" / [2.54mm]. And obviously there will always been the 25.4mm per inch factor between the two so that is pretty easy to figure out.


That's pretty much what I figured. I just wanted to get some validation. When I measure the part with a caliper the top width dimension is 4.9mm, which is within the values given in the datasheet, which lead me to believe they are high/low values. I also found some ASME literature that seems to indicate values displayed this way are high/low values, although there many other ways to display dimension limits.

Thanks for all your help!
Graham Hinton
l3v3l6 wrote:
Looking at the datasheet for a component I see in the package dimension description, size values with a number over another number like this.

5.11
-----
4.90

Does this indicate the maximum and minimum values for a dimension?


It does, but they have only used that nomenclature to describe the moulded epoxy body which is subject to shrinkage. Other more important dimensions are given as a nominal +/- tolerance.

If you want a TO-92 part just use three pads 0.1" apart, making it as small as the straight leads is harder to solder and harder to desolder.
devinw1
l3v3l6 wrote:
devinw1 wrote:
Generally if you see two numbers high and low that are close, they are limit dimensions. So, a way of expressing the tolerance. ie: 1.5mm +/- .25mm is equivalent to 1.75mm/1.25mm expressed as a limit.

You may, as Pelsea said, see dual units stacked as such, but generally one will be in brackets like this: 0.1" / [2.54mm]. And obviously there will always been the 25.4mm per inch factor between the two so that is pretty easy to figure out.


That's pretty much what I figured. I just wanted to get some validation. When I measure the part with a caliper the top width dimension is 4.9mm, which is within the values given in the datasheet, which lead me to believe they are high/low values. I also found some ASME literature that seems to indicate values displayed this way are high/low values, although there many other ways to display dimension limits.

Thanks for all your help!


Nice. Yeah, my job is a mechanical engineer.. I have a copy of ASME Y14.5-2009 sitting on my desk as we speak smile.
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